Construction Control of Earthfill Dams
Construction Control of Earthfill Dams
Construction Control of Earthfill Dams
US Army Corps
of Engineers
ENGINEER MANUAL
AVAILABILITY
UPDATES
Manual
No. 1110-2-1911 30 September 1995
1. Purpose. The purpose of this manual is to present principles and methods for construction
control of earth and rock-fill dams.
2. Applicability. This manual applies to all Corps of Engineers divisions and districts having
responsibility for construction of earth and rock-fill dams.
3. General. This manual is a guide to construction and inspection of earth and rock-fill dams in
those aspects that pertain to safe and satisfactory performance.
ROBERT H. GRIFFIN
Colonel, Corps of Engineers
Chief of Staff
Manual
No. 1110-2-1911 30 September 1995
Table of Contents
Section I Section II
Earth Fill Test Fills
Excavation, Handling, and Rock Test Fills . . . . . . . . . . . . . . . . . . . 5-4 5-1
Hauling Equipment . . . . . . . . . . . . . . 4-1 4-1 Earth Test Fills . . . . . . . . . . . . . . . . . . . 5-5 5-5
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Section V Appendix B
Rock Fill Methods of Relating Field Density
General . . . . . . . . . . . . . . . . . . . . . . . . . 5-21 5-21 Data to Desired or Specified
Hard Rock . . . . . . . . . . . . . . . . . . . . . . 5-22 5-21 Values
Soft Rock . . . . . . . . . . . . . . . . . . . . . . . 5-23 5-22
Appendix C
Section VI Field Compaction Control Forms
Semicompacted Earth Fills and Supplemental Instructions
Uses . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-24 5-22
Specifications . . . . . . . . . . . . . . . . . . . . 5-25 5-22 Appendix D
Construction Control . . . . . . . . . . . . . . . 5-26 5-22 Instructions for Preparing Periodic
Summaries of Field Compaction
Section VII Control Data on Earth and
Sequence of Placement and Rock-Fill Dams
Measurement of Quantities
Schedule of Construction . . . . . . . . . . . . 5-27 5-22 Appendix E
Placement Sequence . . . . . . . . . . . . . . . . 5-28 5-22 Description and Use of Instruments
Measurement of Quantities . . . . . . . . . . . 5-29 5-23 During Earth and Rock-Fill Dam
Construction
Section VIII
Slope Protection Index
Areas to be Protected . . . . . . . . . . . . . . . 5-30 5-23
Upstream Slope Protection . . . . . . . . . . . 5-31 5-23
Downstream Slope Protection . . . . . . . . . 5-32 5-25
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Figure 2-1. Example of resident engineer’s staff organization for large earth dam project
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Figure 2-2. Example of resident engineer’s staff for small earth dam project
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Discrepancies resulting from variations in testing equipment earth or rock-fill dam should visit the project during
and techniques should be carefully avoided. Water content, construction and assist field personnel in interpreting plans
compaction, relative density gradation, and Atterberg limits and specifications and observe problems that may not have
tests are the most common tests conducted. Water content been fully evaluated in the design. Visits should also be
and compaction tests are used for control of cohesive soils made whenever unexpected conditions are encountered that
in impervious and random fills. Atterberg limits tests may may require changes in the plans or specifications. A
be used for control of fills of fine-grained cohesive soils cooperative attitude must be maintained between design
where good correlations of optimum water content and engineers and construction personnel so that mutual
maximum dry density with the Atterberg limits have been understanding is reached on existing problems and feasible
established. Gradation and relative density tests are used for solutions are developed. In some cases, conferences at the
control of pervious fills. Gradation tests are also used for construction site may be necessary between construction
control of rock fill. Field density tests are performed on the personnel, designers, and specialists to review conditions
fill, but compaction tests on the material and water content and determine if design modifications are required. A
determinations may be made either in the central laboratory regular schedule of visits should be set up so that design
or in the field. The central laboratory must have equipment personnel and representatives from the division office and
for these tests, but supplemental portable units may be HQUSACE can inspect field conditions at critical con-
advisable for gradation, compaction, and water content struction stages.
testing at remote locations. Panel pickup trucks are often
used to transport equipment for field density testing, c. Instrumentation. Instrumentation of earth and rock-
undisturbed (record) sampling in the fill, and sampling in fill dams is becoming increasingly important. The main
borrow areas. Specially equipped pickup trucks with a reasons are that many higher earth and rock-fill dams are
small hoist may be required where large-scale field density being constructed, sites having unfavorable foundation con-
tests are to be performed on material such as rock fill or ditions must be used more frequently, interest is increasing
soils with a high percentage of large gravel sizes. in obtaining meaningful data for evaluating dam behavior,
and continually increasing downstream land development is
2-3. Assistance by Higher Echelon increasing the consequences of failure on property damage
and loss of life. Monitoring of pore water pressure, settle-
Unusual conditions encountered during construction ments, and deformations of the foundation and embankment
generally require special attention. The advice of specialists is necessary to check the safety of the dam during con-
in soil and rock mechanics, geology, and instrumentation of struction and to control the rate of construction. The
earth and rock-fill dams, and additional evaluation by design instrumentation must be of the proper type, placed in critical
engineers are often required to obtain effective solution to locations, and installed properly. Valid readings depend on
unusual problems and conditions. techniques and procedures used in installing and observing
the instrumentation. For this reason, specialists experienced
a. Geologists and soils engineers. Specialists with in field instrumentation should plan and supervise the field
experience in soil and rock mechanics, geology, and in- installations. These specialists can be from the district
strumentation are found in division and district offices, at and/or division office, from WES, or from firms specializing
Headquarters, U.S. Army Corps of Engineers (HQUSACE), in installations of instrumentation of earth and rock-fill
Waterways Experiment Station (WES), and on Corps of dams. This applies whether the instrumentation is furnished
Engineers boards of consultants. The services of soil and and installed by the Government or furnished and installed
rock mechanics engineers and geologists are particularly by the contractor. Because proper interpretation of in-
valuable during early stages of construction when the foun- strumentation data is vital to the safety of the dam, the
dation, abutment, and any diversion tunnels or excavations responsibility for collecting and reporting data to the Engi-
(such as for spillway foundations) expose existing condi- neering Division should be carefully delegated. Installation
tions. At this time, it is vital that actual conditions be and observations of instrumentation are discussed in para-
evaluated to determine if they are consistent with conditions graph 6-5; the general use of instrumentation is described in
assumed for design. In addition, it is necessary to recognize Appendix E and by Dunnicliff (1988).
any unusual conditions that may affect construction. The
advice of specialists in soil mechanics and rock mechanics 2-4. Records and Reports
is also valuable in establishing, from observed field con-
ditions, modifications that may significantly improve the Construction records and reports are needed to document
design without increasing the cost of the project. results of tests made to verify specification requirements and
action taken to correct deficiencies and to provide a record
b. Design engineers. The engineer who designs the describing the field conditions, modifications to plans and
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specifications, construction procedures, sequence of opera- faults, artesian and other groundwater conditions, and other
tions, and the location and as-built dimensions of important characteristics or conditions of foundation materials. A
features. These are necessary to evaluate claims made by complete history of the project in narrative form should be
the contractor based on changed conditions, or claims by the written, giving the schedule of starting and completing
Contracting Officer that work performed does not meet various phases of the work, describing construction methods
contract requirements. Progress reports are also needed for and equipment used, summarizing quantities of materials
the district office and to provide a basis for payments to the involved, and including other pertinent data. Foundation
contractor for work accomplished. Inspectors must maintain reports should be supplemented by photographs that clearly
a daily inspection report (or log), and a master diary must depict foundation conditions. Routine photographs should
be kept by the Resident Engineer. The required content of be taken at regular intervals, and additional pictures should
these documents is outlined in EM 415-1-302, “Inspection be taken of items of specific interest, such as the preparation
and Work Records.” Details of specific construction control of foundations and dam abutments. For these items, colored
records and reports are described in Chapter 7. photographs should be taken to provide a better depiction of
construction conditions. The captions of all photographs
a. Construction records. These records provide useful should contain the name of the project, the date on which
data for designing future alterations and additions to the the photograph was taken, the identity of the feature being
structure, determining causes of later undesirable movement reported, and the location of the camera. In reports
or seepage, or interpreting piezometric data. As-built containing a number of photographs, an alternative would be
drawings, construction photographs, descriptions of foun- an index map with a circle indicating the location of the
dation conditions encountered and various treatments, camera with an arrow pointing in the direction the camera
compaction data, and test data on record samples should be was pointing, with each location keyed to the numbers on
included in the records. the accompanying photographs. Details concerning the use
and preparation of construction foundation reports are
b. Construction reports. The construction foundation presented in ER 1110-1-1801.
report should include details such as dip and strike of rock,
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be done for foundation areas under the embankment unless subsequent fill operations should avoid dislocating the
specifically permitted by the plans and specifications or concrete. Hand methods involve removal of all loose or
approved by the design office, as the effects of a lightly “drummy” rock (rock that sounds hollow when struck with
compacted layer at the base of the dam could adversely a steel hammer or bar), and the scaling down of sloped
affect stability. surfaces to provide an even, uniform slope.
(5) Preparation of soil abutments prior to fill placement (3) Washing the hard rock foundation surface with water
should be the same as that for soil foundations. To ensure under high pressure and dry brooming to remove loose
bonding of the embankment to the natural soil of the residue are generally the last step in foundation preparation.
abutments, it is necessary to remove some of the abutment This is done to clean the surface to the maximum extent
surface soil. Inspection should confirm that all loose, wet, possible and to remove fines that may have worked into
or soft soils are removed. In addition, abutment slopes seams. All seams or cracks should be cleaned to a depth of
should be smooth and as flat as economically feasible at at least twice their width. Removal of these fines will
contact with the embankment to improve compaction of fill facilitate complete filling of seams in subsequent operations
against the abutment and to minimize the probability of (such as dental treatment) taken to prevent seepage.
differential settlement causing cracking (paragraph 3-4a(5)). Pressure washing also serves to detect rock projections
Depressions should be filled with concrete or soil compacted overlooked during hand excavation which might otherwise
at proper water contents to densities equal to or greater than work loose during compaction of the first lift or lifts of fill.
those of the materials to be placed above them in the Washing should be performed to clean from higher
embankment fill. See paragraph 3-4a(2) for discussion of elevations to lower elevations.
treatment of abutment slopes of clay shales.
(4) Particular attention should be given to cleaning
b. Rock foundations and abutments. openings that cross the axis of the dam. Accumulated water
from the washing process must be removed. Small air
(1) After all rough excavations of overburden and/or pumps, hand bailers, or aspirators may be used to empty
weathered rock have been completed, all grouting is narrow, water-filled fissures. If the foundation consists of
completed, and the surface of the rock foundation is blocky rock with frequent joints, caution must be used to
exposed, shaping and cleaning operations should begin. avoid removal of satisfactory foundation material (such as
Shaping and cleaning a rough rock foundation are necessary stiff clay in joints) by overzealous pressure washing. When
to provide a smooth, uniform, and clean surface against the nature of the rock is such that it could be softened by
which fill can be compacted. The procedure generally washing with water, compressed air should be used instead
consists of removing large loose rocks, overhangs, and of water. Air pressure is also often used as a final step in
projecting knobs by scaling, handpicking and wedging, and cleaning sound rock surfaces. Figure 3-1 shows the rock
light blasting pressure washing followed by some form of foundation at DeGray Dam being cleaned with compressed
“dental treatment” to fill all holes, cracks, joints, crevices, air.
and depressions. Dental treatment involves cleaning the
cavities and backfilling them with concrete, and is discussed
in more detail in paragraph 3-4b(3). The resident geologist
or embankment engineer should inspect and approve this
phase of the work.
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(5) Where rough and irregular surfaces remain after hand geologist and embankment engineer, should be made. Some
excavation, troughs, pits, and other depressions are filled common types of cutoffs are discussed in the following
with concrete to provide a more even surface on which the paragraphs.
first layer of the embankment may be compacted. As
previously noted, this procedure is termed dental treatment (1) Compacted backfill trenches. Backfill compacted
and is discussed further in paragraph 3-4b(3). If foundation into a seepage cutoff trench is one of the most effective
grouting has been performed, cleanup operations should construction devices for blocking foundation seepage.
include removal of any spilled or washed grout that might Material and compaction requirements are the same as for
otherwise conceal surface imperfections and pockets of the impervious section of the embankment. When required
undesirable material. by contract specifications, the trench must fully penetrate the
pervious foundation and extend a specified distance into
(6) Before placing the first layer of embankment unweathered and relatively impervious foundation soil or
material, the cleaned and prepared rock surface should be rock. Treatment (as described in paragraph 3-2a) of the
moistened, but no standing water should be permitted. exposed surface in the bottom and sides of the trench is
Moistening the rock surface is recommended instead of essential to ensure firm contact between foundation and
using overly wet soil in the first lift to obtain good contact. backfill. The trench excavation must be kept dry to prevent
Use of heavy pneumatic equipment (preferably a rubber- sloughing of the side slopes and to permit proper backfill
tired roller) is recommended for compacting the first lift on placement and compaction. When the water table is near
rock surfaces. This will enable the rock surface to be kept the ground surface, dewatering the excavation is required
intact, especially where the rock surface is irregular or and is frequently a major expense in cutoff construction.
composed of thin beds of alternating hard and soft rock. Dewatering and drainage methods are discussed in para-
graph 3-5. In any trenching operation, a qualified geo-
(7) Foundations consisting of compaction-type shales and technical engineer should inspect the construction at regular
slaking tuffs should be protected from disintegration caused intervals to monitor stability of the side slopes.
by drying due to exposure to air. The handling of clay
shales is discussed in paragraph 3-4a(2). (2) Slurry trenches.
(8) The same degree of care should be exercised in (a) The slurry trench method of constructing a seepage
abutment treatment as in foundation treatment. A good cutoff involves excavating a relatively narrow trench with
bond between the embankment and the abutment is critically near-vertical walls, keeping the trench filled with a bentonite
important. Areas to be cleaned at rock abutments should slurry to support the walls and prevent inflow of water, and
include not only those beneath the embankment core but then backfilling with a plastic impervious mixture of well-
also those beneath transition or filter zones. Within these graded clayey gravel to protect against piping, to reduce
areas, all irregularities should be removed or trimmed back seepage, and to minimize consolidation of the backfill
to form a reasonably uniform slope on the entire abutment material.
with vertical surfaces no higher than 5 ft. Benches between
near-vertical surfaces should be of such width as to provide (b) The backfill should be a mixture of impervious
a stepped slope comparable to the slope on adjacent areas borrow, sand, gravel, and bentonite slurry (U.S. Army
but not steeper than 1V on 1H. Overhangs should not be Engineer District, Savannah 1968). The backfill may be a
permitted at any locations. Methods of overhang removal mixture of material excavated from the cutoff trench and
are discussed in paragraph 3-4b(4). other material to provide an acceptable blend.
(9) The treatment of cracks, fissures, and other (c) Depending on the required depth, the excavation may
undesirable conditions in rock foundations and abutments is be accomplished with a dragline, backhoe, clamshell, or
discussed in paragraph 3-4b(2). trenching machine. A trenching machine is limited to
depths less than about 40 ft, provided no cobbles exist.
3-3. Seepage Control Unmodified backhoes are limited to depths less than about
45 ft but with special modification can reach depths of 55
a. Cutoffs. Foundation cutoffs or core trenches serve as to 60 ft; their main advantage is that they can be used in
barriers to underseepage. The design of foundation cutoffs areas where cobbles exist. Maximum depths of about 100 ft
is based largely on borings made during field investigations have been achieved with a dragline. Required equipment
for design. Therefore, the open excavation of a cutoff modifications for excavation to a great depth (with a drag-
trench provides the first real look at actual foundation line) include weighting the bucket to overcome the buoyant
conditions; frequent inspections, particularly by the field effect of the slurry and providing heavy-duty bearings and
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hydraulic systems. A dragline excavating a slurry trench is 1967; U.S. Army Engineer District, Savannah 1968). A
shown in Figure 3-2. scraper blade was attached to the bucket which, when
dragged along the bottom of the trench, removed coarser
(d) The specific gravity of the slurry must be high soil particles and some of the finer loose material at the top
enough to ensure that hydrostatic pressure exerted by the of the rock. An air jet was used to remove sand, gravel,
slurry will prevent caving of the sides of the trench and yet and other undesirable material from potholes, cracks and
not be so high as to limit the depth to which the excavating crevices; these materials subsequently became entrained in
bucket will operate. Typical values of specific gravity of the slurry. Suction and discharge pipes were used to remove
slurries used in past jobs range from 1.05 to 1.2, with some contaminated slurry (from the trench), which was cleaned by
values as high as 1.5. The slurry level is generally sending it to shallow sediment ponds along the sides of the
maintained 2 to 3 ft above the groundwater level. trench where the contaminants settled out of suspension.
The clean slurry was then placed back into the trench.
(e) Procedures for cleaning the bottom of the trench, Mechanical desanders are available and may be desirable or
removing sand which settles out of the slurry, continuous even required for removing sand (from the bottom of the
control of viscosity and specific gravity of the slurry, and trench) in some situations. The bottom of a trench should
mixing and placing the backfill are critical in achieving be sampled after it has been cleaned to ensure that it is
successful results. An example of successful slurry trench properly free of undesirable material.
construction is that at West Point Dam, Chattahoochee
River, Alabama and Georgia, in which the bottom of the (f) After the bottom of the trench has been cleaned,
trench was cleaned with a modified dragline bucket (Jones backfill is placed in the trench with a clamshell to form a
gentle slope parallel to the axis of the trench; backfill is
then successively pushed into the trench with a bulldozer
and allowed to slide down the slope, intermixing with and
displacing the slurry. The slope of the backfill should be
flat enough to prevent sliding and sloughing. The trench
surface should be observed/inspected as long as possible to
detect unusual settlements which might indicate slurry
pockets entrapped during the backfilling process. A sketch/
schematic of the progressive excavation and backfilling
scheme used at West Point Dam is shown in Figure 3-3.
The ultimate objective is to achieve a positive cutoff by the
combined effects of the backfill and a “filter cake” formed
on the sides of the trench by the slurry. Since the integrity
of the filter cake after backfill placement cannot be assured,
it is recommended that the added benefit of the cake be
considered as an additional safety factor with the backfill as
the primary element of seepage cutoff.
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Figure 3-3. Progressive excavation and backfilling scheme for slurry trench construction
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installation of rock bolts and other structural support characteristics. In this way, the impact of a problem deposit
features by plans and specifications. Drainage galleries at can be properly evaluated in relation to the original design.
the base of a dam or in an abutment of soil or weathered Some common undesirable conditions are discussed in the
rock are usually concrete-lined tunnels. Inspection of following paragraphs.
concrete-lined tunnels requires knowledge of concrete
placement and backfill practices around concrete structures a. Unfavorable soil conditions.
in addition to knowledge of grouting and seepage control in
pervious soils. Inspection of concrete, including proper (1) Highly compressible and low strength soils. Organic
placement techniques, is thoroughly discussed in the ACI soils exhibit high compressibility and low shear strength and
Manual of Concrete Inspection (1967). EM 1110-2-2000 are generally recognized by their dark color, the presence of
also contains information related to the inspection of organic particles, and often a distinctive “organic” odor.
concrete placement. Inorganic clays with high water content also exhibit high
compressibility and low shear strength. If an embankment
(4) Toe drains. is constructed on a deposit of either highly organic soil or
highly compressible inorganic soil, excessive differential
(a) Toe drains collect and facilitate removal of seepage settlement could cause cracking of the embankment, or
water at the downstream toe of the dam to prevent form- shear failure might occur; if significant deposits of either of
ation of soft boggy areas and/or boils. Toe drains are these materials are discovered during early construction,
generally connected to the horizontal drainage blanket and their extent should be established and, if it is feasible, they
sometimes to the relief well system to collect and remove should be removed and replaced with acceptable compacted
seepage water in thin pervious strata in the upper foundation backfill. If extensive and/or deep deposits of such materials
that the deeper relief wells cannot drain. are found, engineering personnel should be consulted to
determine if design modifications (such as flattening
(b) Toe drains generally consist of a trench containing a embankment slopes or adding berms) are required.
perforated collector pipe surrounded by filter gravel with the
remainder of the trench backfilled with sand. Particular care (2) Clay shales.
must be exercised in placement of the backfill. Unless the
sides of the trench are approximately sloped at the angle of (a) Clay shales are among the most troublesome and
repose of the filter material, a wood or steel form must be unpredictable soils. They are often termed “compaction” or
used to keep the filter layers separated as the backfill is “soil-like” shales if they have been highly overconsolidated
brought up. Additionally, filter materials must be protected by great thicknesses of overlying sediment and have no
from contamination which could result from inwash during appreciable cementation. Clay shales tend to slake rapidly
a rainstorm. Construction (backfilling) of toe drains in short when subjected to cycles of wetting and drying; some
sections could minimize contamination. exhibit very high dry strength, but upon wetting swell and
slake profusely, losing strength rapidly. They vary in color
(c) The same control procedures are used for toe drains from brown to green to black and are often slickensided (a
as those that are used in construction of impervious fill in slickenside is a smooth, shiny, striated, discontinuous
the main embankment; these are described in Section IV of surface that shows evidence of movement). Problem clay
Chapter 5. Gradation tests on filter materials should be run shales can be identified on the basis of slickensides found
at least twice each day during placement operations. Stock- by breaking undisturbed blocks or chunks apart, and from
piled as well as in-place filter material should be tested. the speed of slaking during cycles of wetting and drying.
Handling and compaction of the filter material must be Clay shales that are slickensided may be unstable even in
closely controlled to avoid segregation and particle relatively flat slopes. Rapidly slaking shales will deteriorate
breakage. into soft clays with low strength upon exposure to air and
water and require protection of exposed surfaces prior to fill
3-4. Treatment of Unfavorable Conditions placement. Stability in deposits of problem clay shales is
further compounded if they are highly fractured or jointed
Unexpected unfavorable conditions are frequently discovered or show evidence of faulting.
during early construction, and may range from undesirable
deposits of material not detected in exploratory drilling to (b) Some clay shales also tend to swell or expand
adverse seepage conditions that were impossible to predict. considerably when unloaded by excavating overlying
Very often, when undesirable materials are found, additional material. Expansion may progress deeper into the clay shale
exploration by test pits, borings, or calyx holes is necessary deposit with time and cause nonuniform rebound across
to define the extent of the unexpected deposits and their excavation surfaces. This is caused by stored strain energy
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that is released with time after overlying materials are under high stress. If an embankment is founded on a
removed. Therefore, excavating in clay shales should be collapsible soil which is subjected to wetting for the first
completed and backfilled without delay. The last foot or so time, substantial settlement and possibly cracking in the
of excavation into a slaking clay shale should be deferred overlying embankment could result. Therefore, unaltered
until just prior to backfill operations in order to minimize collapsible soils should not be allowed in a dam foundation.
the time of exposure of the final clay shale surface. During If it is not practicable to remove such deposits, they should
winter, the depth of cover should be no less than the frost be treated to break down their structure prior to
penetration depth; operating in this manner will provide a construction.
fresh surface to compact the fill against and eliminate the
chance of a soft stratum between the unweathered shale and (b) Prewetting has been used as a treatment for collapsi-
the fill. This is generally a costly procedure for steep ble soils; the deposits are flooded with water in flat areas
slopes, but becomes more economical for slopes flat enough where ponding is possible, or by continuous sprinkling on
for equipment to work on. slopes where ponding is not possible. Later, as the embank-
ment is constructed, its weight compresses the foundation
(c) Only rubber-tired equipment should be used in final soil, causing primary consolidation to take place during
excavation, cleanup, and initial fill placement on clay shales construction rather than a sudden and possibly catastrophic
to minimize disturbance. Final clay shale surfaces should foundation collapse when the reservoir is filled for the first
not be scarified prior to covering with fill. If pressure time.
cleaning is required, only air pressure (i.e, no water) should
be used. (4) Loose granular soils. Loose, water-saturated sands
and silts of low plasticity may have adequate shear strength
(d) Various types of coatings have been applied to under static loading conditions; however, if such materials
protect exposed clay-shale surfaces; they include gunite, are subjected to vibratory loading, they may lose strength to
sprayed asphalt, and other bituminous materials and resin the point where they flow like a fluid. The process in
emulsions. Gunite is reliable when reinforced and anchored which susceptible soils become unstable and flow when
to the shale, but particular care must be exercised to avoid shocked by vibratory loading is called liquefaction, and it
a drummy condition. This type of protection was success- can be produced by vibration from blasting operations,
fully used at Waco and Proctor Dams in Texas. Although earthquakes, or reciprocating machinery. In very loose and
bituminous coatings and resins have been used successfully, unstable deposits, liquefaction can occur as the result of
they do not always provide adequate protection for the clay disturbances so small that they are unidentifiable. Loose silt
shale. At Waco Dam, an asphalt emulsion membrane used and sand deposits have been compacted by blasting
on near-vertical cuts was not always adequate, even with (Layman 1942), vibroflotation, and driving compaction
multiple application. Evidence of its inadequacy was that piles; however, the effectiveness of these procedures for
the shale surfaces spalled and slaked. Concrete slabs, deposit densification is not predictable. Vibroflotation has
whether placed specifically for protective purposes or as been successfully used in treating limited areas, but it is
slabs for an overlying structure, provide good protection. very expensive. Blasting is generally not effective in
Exposed surfaces may also be protected by wet mats. densifying loose granular deposits because the vibratory
Burlap has proven to be an unsatisfactory mat because it is energy produced is of such high frequency.
too porous to retain water for any length of time. Maxi-
mum allowable exposure time can vary from a few minutes (5) Steep abutment slopes. Steep abutment slopes of
to several hours depending on the characteristics of the shale earth tend to increase the possibility of transverse cracks
and the prevailing weather conditions. developing in the embankment after construction. During
construction, they may become unstable and endanger
(3) Collapsible soils. construction personnel. Slides can occur in clays, sands,
and gravel, particularly in slopes subjected to seepage.
(a) “Collapsible” soils are generally soils of low density Slides may damage completed works and require costly
and plasticity which are susceptible to large decreases in repairs. In many cases, it may be necessary to bench the
bulk volume when they are exposed to water. Collapsible slopes to provide safety against sloughing material and
soils are characterized by bulky grains (in the silt-to-fine- sliding. Frequent inspection should be made by the resident
sand grain size) along with some clay. Collapse results from geologist or other experienced personnel to determine
softening of clay binder between larger particles or the loss whether flattening of specified slopes is required.
of particle-to-particle cementation due to wetting. Volume
change from collapse occurs rapidly (relative to consoli- (6) Old river channels. Old abandoned river channels
dation) and can be very significant especially if the soil is filled with pervious or impervious materials are often
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encountered unexpectedly during construction. As men- (2) Open joints and fractures. All open joints, cracks,
tioned earlier, the extent of these deposits is often fissures, and fractures in the foundation rock surface must
impossible to establish accurately during the exploratory be filled to prevent erosion or scour of embankment material
stages, and in some cases an entire deposit may be missed. at the rock contact. A sand-cement mortar is generally used
Old river channels beneath a dam foundation, filled with to fill these openings. The mortar is worked into the
course-grained pervious material, would constitute a fractures using a stiff broom, taking care to prevent the
dangerous open path of seepage. Channel fillings of soft accumulation of mortar on unfractured surfaces, where it
fine-grained materials can cause differential settlements and would not be needed in any event and might be harmful if
cracking of the embankment if not removed and replaced it cracked or broke off during rolling of embankment fill.
with properly compacted material. Where the existence of The water-to-solids ratio of the mortar should be varied as
such deposits has been revealed, additional exploration by required to accommodate the conditions encountered. If the
borings, test pits, etc., to establish their extent may be rock is closely fractured with fine cracks, the water content
necessary. The design engineer can then decide what may be increased and a fine sand used to permit easy entry
measures will have to be taken to modify the design or to of the mortar into the minute seams. If wide, deep cracks
remove the deposit. An old river channel found during are present, a stiffer mortar with coarser sand should be
foundation excavation for the core trench at Fall Creek employed to reduce the extent of shrinkage cracking (in the
Dam, Fall Creek, Oregon is shown in Figure 3-4. cured mortar). A rock surface after mortar treatment is
shown in Figure 3-5.
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Figure 3-6. Solution channel, Mississinewa Dam, Figure 3-7. Abutment overhang, DeGray Dam,
Indiana Arkansas
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Figure 3-11. Dewatering systems Figure 3-13. Sand boils at Friars Point, Mississippi
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Chapter 4 of the ladder (usually around 40 ft, but lengths greater than
Borrow Areas and Quarries 75 ft are not uncommon).
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blending operations, water additions, etc. Transfer points sloping screens, whereas the larger (rock) particles tumble
(where the material is transferred from one belt to another) down the sloped screens and fall over the edge onto a pile
are usually required. Automatic facilities for loading trucks or a conveyer belt. Each type of separator is discussed in
at the terminal points can be easily provided, or sometimes more detail in paragraph 4-4c. Various plants have capa-
the material can be dumped directly from the belt onto the cities ranging from 100 to 2,000 cu yd/hr, but most plants
embankment, spread with bulldozers or grader, and process 300 to 500 cu yd/hr. Wet materials having appre-
compacted. ciable clay content are the most difficult to process, since
the clay tends to clog the screen openings.
(3) Separation plants. Separation or screening plants
(Figure 4-5) are employed where it is desired to separate 4-2. Borrow Area Operation
different particle sizes of a granular material. Generally, the
purpose is to remove oversize rocks or cobbles to facilitate a. Plans for development. The contractor should be
compaction or to remove fines from filter material. There required to submit detailed plans prior to construction for
are four principal types of screening plants: the development of borrow areas and quarries. These plans
should be carefully reviewed prior to approval and rigidly
(a) Horizontal or sloping stationary screens. With this followed during construction.
equipment, material is directed through a stack of stationary
screens/sieves with screen opening sizes decreasing toward b. Inspection. Inspection of borrow pits includes
the bottom of the stack. Larger soil particles are retained on observing and recording all earthwork operations performed
the upper screens while smaller particles fall through to be in the borrow pit prior to dumping the material on the
retained on a lower screen. embankment. Working under the supervision of the con-
struction engineer and chief inspector, the borrow pit
(b) Vibrating screens. This equipment is basically like inspector observes areas excavated, depth of cut, and ade-
the stationary system described above except that soil quacy of the contractor’s equipment for the tasks at hand.
separation through the screens is facilitated and expedited by Inspectors should inform the chief inspector of conditions
vibrating the screens. that deviate from the plans and specifications, so that
corrective action can be taken if necessary; these deviations
(c) Rotating trommels. This equipment consists of an include:
inclined rotating cylinder with screens or holes of different
sizes around the periphery. Separation is accomplished (1) Borrow materials that are different from those
when soil particles of different sizes fall through the appro- expected to be obtained in the borrow area.
priate hole size as the mixed material rolls around inside the
rotating cylinder. (2) Borrow excavation operations that are not producing
the desired blend or type of material required.
(d) Wobblers (or rotating cams). In wobblers, rotating
cams produce vibrations which cause fines to fall through (3) Borrow materials that are too wet for proper
Figure 4-4. Belt conveyor system Figure 4-5. Vibrating screen separating plant
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compaction. During excavation and processing, the in- soil is being processed through a screening plant to remove
spector observes all adjustments made to the water content oversize cobbles, a considerable amount of water can be
of the material. If separation or blending is required, the blended into the soil by sprinkling within the plant.
inspector performs tests to ensure that the soil type and/or
gradation of the processed material meets the specifications. (2) Wet soils.
c. Water content control. Water content changes occur (a) It is generally easier to add water to dry soil than to
in borrow pits because of rain, evaporation, or the addition reduce the water content of wet soil. The difficulty of
of water for the direct purpose of raising the borrow lowering the water content of a soil deposit will depend on
material water content. Earthwork contractors should be the plasticity of the deposit and on the amount and type of
encouraged to take steps to hold the water content of the rainfall during construction. The rainfall pattern is im-
excavated borrow material as close to the desired placement portant; for example, a few scattered cloudbursts are less
water content as possible prior to delivery to the embank- harmful than the same amount of precipitation falling as rain
ment. over a longer period of time. It is practically impossible to
dry out borrow material to any extent without excessive
(1) Dry soils. work and cost unless a dry season of sufficient length
permits evaporative water loss.
(a) For most clays it is not desirable to add more than 3
to 4 percent water on the fill, and in arid regions the (b) The first step in either drying out or maintaining the
average natural water content of soils in borrow areas may in situ water content of borrow material is to provide
be 10 to 15 percent below the desired value for compaction. surface drainage in the borrow area; this is done by cutting
Under such conditions, irrigation of borrow areas generally ditches and sloping surfaces to drain to these ditches. Since
results in more uniform water content distribution, while water is drained away from the borrow material, absorption
also being the most economical method of adding water. of subsequent rainfall is minimized. Wet soil can some-
Borrow areas are frequently wetted to depths of 5 to 15 ft times be dried by ripping, plowing, disking, or otherwise
or more by surface irrigation. aerating the soil to a depth of several inches. The time
required for drying (and hence the production of usable
(b) The water content of soils in a borrow area may be material) will depend on soil plasticity, the depth to which
increased by constructing low dikes and ponding/flooding the material can be aerated, and climatic conditions. After
the area or with a pressure sprinkling system. Controlled the soil has dried to a usable water content, it may be
ponding/flooding is most suitable in low-lying flat areas and removed with elevating scrapers or graders and the process
tight soils for which long wetting periods are needed. of aeration, drying, and removal repeated. The procedure
Sprinkling is advantageous on sloping ground and in large described is relatively effective for silty and sandy soils, but
borrow areas where only relatively shallow wetting is is not effective for plastic clays; if the water content of
needed. It is desirable in some borrow areas not to strip plastic clays is lowered by aeration in dry climates, the
topsoil before ponding/flooding, since stripping tends to seal result may be hard dry chunks which are difficult to
natural holes and cracks in the ground surface which process. Open ditches in borrow areas of sandy and silty
facilitate the entry of water. Ripping tight surface layers soils with a high water table will drain off excess water and
has been found effective in speeding up the wetting process. lower the water table.
When sprinkling is used on hillside/sloped borrow, it may
be desirable to use contour plowing to prevent surface (c) In the construction of Dorena Dam, Oregon, by the
runoff. Good judgment should be used in prewetting steep Portland district, disking the borrow areas did not break up
hillside borrow so that slides are not induced. The length of and mix the clay material enough to obtain uniform water
time required for wetting/hydration may vary from a few content distribution within the soil. This problem was
days to several months, depending on soil permeability and solved by using a heavy rotary pulverizer pulled by a
the depth to which moistening is desired. A curing period crawler tractor after the disking. Shortly after pulverizing,
is desirable after wetting to allow added water to be the material was at or near placement water content, was
absorbed uniformly by the soil. The time needed and the easy to load, and was in excellent condition for compaction.
best technique to use can be determined by experimentation.
(d) In very wet climates and adverse weather conditions,
(c) If general borrow pit irrigation is not satisfactory, it may only be possible to prevent borrow material from
supplemental water can be added by sprinkling the face of becoming wetter during construction. This may be accom-
a shovel excavation; the water is mixed into the matrix as plished by such techniques as providing surface drainage
the material is shoveled, hauled, dumped, and spread. If and/or using equipment that minimizes the chance for
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material to absorb additional water. Excavating with power also aid in preventing undesirable mixing of soil types. For
shovels on a vertical face is an example of this strategy. instance, stratified deposits of distinct soil types to be kept
separate should be excavated with a scraper since scrapers
d. Blending soil layers with excavating equipment. excavate by cutting relatively thin strips of soil, thereby
avoiding mixing of strata. Screening plants are sometimes
(1) Blending two or more soil types may be required employed to obtain required gradations. Although screening
where different soil strata are present in borrow areas or of natural materials for major embankment volumes is an
required excavation. Reasons for blending soils are to expensive process, it may not be excessively so when
obtain borrow materials having acceptable characteristics for compared with the benefits. The use of screening plants
a particular embankment zone and to utilize borrow may avoid major placement problems, allow steeper em-
materials so stratified in situ that it would not be feasible to bankment slopes, and employ a lesser volume of material.
load and place material from individual soil strata. Screening is used most often in connection with filter
materials.
(2) Where materials to be blended occur as horizontal
strata, shovels, draglines, wheel excavators, or in some (3) If any materials are encountered in borrow areas
cases, scrapers have been used to blend them during having characteristics that differ appreciably from those
excavation. Excavation with a power shovel on a vertical anticipated, such materials should not be used unless
cut will blend the materials. Where more extensive mixing approved by the design office.
is required, it can be achieved by running the open bucket
through the mixture several times before loading. Con- (4) The borrow pit inspector must ensure that materials
struction control in this case will require maintaining the of possible short supply are conserved.
height of cut necessary to obtain the desired proportions of
each type of material and to ensure that the materials are f. Oversized materials. The maximum diameter of
blended thoroughly. stone or cobble allowed in compacted fill is generally
limited to about three-fourths the thickness of the compacted
(3) Blending different materials from different sources layer. Where a high percentage of oversized cobbles or
can be accomplished by stockpiling one layer on the other stones is present, oversize material removed may be used in
so that excavation can be made through the two materials as the outer portions of the dam. Oversize materials can be
in a stratified natural deposit. However, this procedure is removed on the fill surface by hand labor or by special
expensive and is seldom used. rakes mounted on tractors, or they can be screened out in
the borrow areas. Generally, removal of oversized rock is
(4) Scrapers have been used to mix stratified deposits by more efficiently accomplished in the borrow areas. Rock
developing the excavation in such a way that the scraper is separation plants are usually employed for this purpose.
loaded on an incline, cutting across several horizontal strata Processing methods are discussed further in paragraph 4-4c.
of different materials; however, this procedure is generally
not as effective in mixing as the use of a shovel, dragline, g. Stockpiling. When excavation of fill material from
or wheel excavator. borrow sources progresses at a faster rate than its placement
in the embankment, the material can be stockpiled near
e. Selection of materials intended for different embank- locations where it is to be used. Stockpiling involves
ment zones. expensive rehandling and is generally only used on large
projects where borrow is to be used from an excavation
(1) The borrow pit inspector must assure that materials made before embankment construction, where borrow areas
intended for a certain embankment zone are within specifi- will be flooded during construction, or when material must
cation limits. Selection of materials will, to a large extent, be stockpiled close to its point of intended placement for
have been accomplished on the basis of design studies; that rapid construction of a closure section. Unless stockpiling
is, borrow areas for the various zones will have been is a specified item, its use is at the expense of the
designated. Design studies should have disclosed the nature contractor. Stockpiling is advantageous in cases where
of the materials and the expected ranges of variation. borrow must be transported long distances and moved by
Therefore, field personnel should review the results of all conveyor belt or other means at the site. Filter materials are
investigations and know what materials are acceptable; the often stockpiled when it is necessary to obtain them from
inspector must be able to identify these materials visually as commercial sources or to manufacture them on the site.
far as possible, and with a minimum of index tests. Care should be taken in stockpiling filter materials to avoid
segregation, contamination, and particle breakage. In
(2) The use of proper equipment by the contractor will dumping filter material onto a stockpile, drop heights should
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be kept at a minimum; the filter material stockpile should be with large capacity buckets. In a deep quarry, the walls and
located well away from other types of material, the area face must be carefully scaled as rubbelized material from a
should be sloped so that water drains away from filter blast is cleaned up to prevent rockfall accidents.
stockpiles, and heavy equipment should not be operated over
filter materials. Gradation tests should be performed on (2) The power shovel, either electric or diesel, is still the
samples of filter material from a number of locations around most common piece of equipment for loading directly from
the stockpile before and after it is placed to ensure that the muck pile, although front-end loaders have been used in
specifications have been met. The advantages of this capacity also. The power shovel is generally desired
maintaining stockpile quality should be well understood and because of its large capacity, its powerful bite, and its
appreciated by site personnel, especially if many contractors efficiency in getting the load from the bucket to the carrier.
will use the stockpile.
(3) Front-end loaders are used most often to load
h. Cold weather operations. Borrow area operations processed material from stockpiles. A front-end loader may
can often continue into freezing weather without loss of be either tracked (crawler) or rubber-tired. The crawler type
embankment fill quality. Frost penetration progresses slow- has been used often in the past, but the four-wheel-drive
ly in undisturbed (in situ) fine-grained soils except in rubber-tired type has recently become popular. Although
extremely cold weather, and soils will generally remain the rubber-tired loader lacks the traction of the crawler, it is
unfrozen if borrow operations are conducted continuously. faster and usually has sufficient traction on most surfaces to
Material satisfactory for fill placement can be obtained if the load a full bucket efficiently.
in situ water contents do not require adjustment on the fill.
Sands and gravel can generally be excavated and handled b. Hauling. Trucks are generally used as prime movers
effectively under very low temperatures, but the addition of of rock fill. The three basic truck types are the end dump,
water on the fill for compaction may present problems. the bottom dump, and the side dump. Side dumps are rarely
Borrow excavation in cold weather is usually limited by fill used for the construction of compacted rock-fill dams; they
placement requirements; it should be limited to use only in are more useful for building out the edges of fills. Bottom
special situations and should be practiced with considerable dumps are more frequently used, but they have definite
caution. limitations; they are somewhat unwieldy, and oversize rock
has a tendency to become trapped in their discharge gates,
Section II requiring bulldozers to push them off the rock and thus
Quarries and Rock Excavation costing time and disrupting the hauling schedule. At the
Lewis Smith Dam, Alabama, all bottom dumps had to be
4-3. General taken off the job and replaced with end dumps for this
reason. End dump trucks are probably the most frequently
Even experienced geologists and engineers often cannot used vehicles for rock hauling because of their speed,
predict how rock obtained from a quarry or excavation will mobility, and generally lower first costs to the contractor.
break down after blasting. Consequently, field personnel End dumps vary in size from the light “dump truck” to
must be particularly observant of the contractor’s methods semitrailer types with capacities in excess of 100 cu yd.
and the results obtained. The most frequent trouble occurs Since in most cases hauling from rock excavations and
when the quarried material either contains more quarry fines quarries is “off-the-road” hauling, these trucks are not
and dust or more oversized material than had been subject to size and weight limitations imposed upon carriers
anticipated in the design. It has sometimes been necessary that travel on public highways, thus allowing the large
to make major design changes because rock behavior or capacities.
breakdown was contrary to that anticipated by the designers.
See EM 1110-2-3800 for further guidance on the subject. c. Processing. It is usually necessary to process
fragmented rock produced by blasting since it is unlikely
4-4. Equipment that the required sizes and/or gradation would occur directly
from blasting. Processing may involve removal of oversize
a. Loading. or undersize (fines) material, or obtaining a specific size
range for use in a particular zone of the embankment such
(1) Power shovels and front-end loaders are used almost as a graded filter. Preparations should be made to stockpile
exclusively today for loading trucks or other vehicles in filter material when it is convenient to prepare the proper
rock excavations or quarries. Power shovels have been used gradation; this ensures an adequate supply of filter material
for many years; large front-end loaders have recently come during rainy periods when the screens of a processing plant
into prominence with the advent of more powerful units tend to clog. There are several types of separation or
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processing plants, each with its own advantages and dis- sized opening into hoppers or onto conveyor belts which
advantages; the use and end product desired will dictate the transport the various sizes to stockpiles.
choice of plant. Some of the more common plants are
briefly discussed below. (3) Shaking or vibrating screen. This device is generally
used for sizing. It consists of a metal screen or multiple
(1) Grizzlies. The grizzly is perhaps the most common screens with desired opening sizes, mounted either
separating device; it is used only for removing oversize rock horizontally or inclined on a rigid frame and given either a
from the material which, in some cases, is all that is needed reciprocating motion (in the case of a shaking screen) or a
to obtain the gradation specified. A grizzly consists of a vibrating motion (in the case of a vibrating screen). A
sloped grate made of heavy bars which are wider at the top vibrating screen separating plant is shown in Figure 4-5.
than at the bottom to ensure that particles do not bind Material retained on a given screen passes on to one end of
partway through the gratings and clog the openings between the screen, where it is discharged into a hopper or onto a
the bars. Grizzlies are often constructed with sloped vibrat- belt. More than one size can be separated by having
ing screens or with rotating cams (grizzly wobblers) so that screens of successively smaller openings below the initial
oversize material passes over the grate and falls off the end screen.
while the desired material falls through the grate. Grizzlies
may be constructed in many ways, but they always involve 4-5. Test Quarries
the use of a grate or lattice of heavy bars. Figure 4-6 shows
a sloping grizzly in operation at Gathright Dam, Virginia. a. Test quarries aid the designer in determining the
A grizzly wobbler used at Stockton Lake Dam, Missouri, is sizes, shapes, and gradations of rock produced by excavation
shown in Figure 4-7. and handling. Test quarries are usually operated in con-
junction with a test fill so that all aspects of rock behavior
(2) Trommel. A trommel is a separating device which from blasting to compaction can be evaluated. Variables in
consists of a rotating cylinder of perforated sheet metal or quarrying operations include drilling, blasting techniques,
wire screen. Like the grizzly, it is used for eliminating loading, processing, and hauling procedures and equipment.
oversize particles, but it can also separate the remaining A properly executed test quarry program will provide the
material into various size fractions. A trommel can be open designers and field personnel valuable information pertinent
at either one end or both ends with the axis of the cylinder to cut slope design, evaluation and control of geologic
horizontal or slightly inclined so that the material is structures, best blasting technique, and rock fragmentation
advanced by rotation of the cylinder. Size of the per- control to be used; provide representative materials for test
forations in the sheet metal or of the openings in the screen fills; give prospective bidders a better understanding of the
can be varied to obtain more than one size fraction. As drilling and blasting behavior of the rock; and determine
material is fed into the rotating cylinder, the oversize what processing, if any, of the rock will be required. A test
material passes through and is discharged at the other end,
while each of the fractional sizes falls through a properly
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quarry in operation at Foster Dam, Oregon, is shown in should be familiar with methods of operation that affect the
Figure 4-8. rock fill.
4-6. Obtaining Specified Rock Fill b. Processing. If the contractor cannot obtain the
correct rock sizes by blasting or if special treatment is called
The specifications will prescribe the gradations of the rock for in the specifications, processing will be required. The
fill to be placed in the various zones. It may be possible to degree of processing will vary from using a simple grizzly
obtain acceptable material directly from blasting, but the to remove oversize rocks, or washing to remove excess
rock may have to be processed in one form or another. In fines, to running material through a crusher plant. Rock
any case, the inspector must ensure that the placed rock crusher plants are not generally used for processing rock fill
meets the criteria set forth in the plans and specifications. due to high operational cost. However, crusher plants are
The contractor’s method of operation has a significant effect sometimes used to produce select filter materials such as
on the gradation of rock obtained. Therefore, the inspector transition or bedding material. The amount of processing
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required will depend on the results of the blasting unless in them. All slopes should be scales and trimmed to elimi-
special processing is expressly called for in the specifi- nate the probability of falling rocks and debris. All areas
cations. Different types of separation equipment and their that can support vegetation should be seeded. In some
utilization have been described above. cases, fencing may be needed to restrict free access.
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Chapter 5 Section II
Earth-Fill and Rock-Fill Construction Test Fills
For compaction in restricted areas such as those immediately b. Test fills are often operated in conjunction with test
adjacent to concrete walls, around conduits, or in depres- quarries. This practice not only provides information about
sions in rock surfaces, hand-operated power tampers or rock behavior during quarrying procedures, but also ensures
vibrated plate compactors are used. Power tampers should that material used in the test fill is representative of material
weigh at least 100 lb, and vibrated plate compactors are that will be produced by the proposed excavation. As in
effective only in clean cohesionless backfill. test quarries, test fill programs are often administered by
both construction and design personnel, and it is advisable,
5-3. Spreading and Processing Equipment when possible, to assign construction personnel involved in
the test fill program to actual dam construction.
Spreading and processing equipment commonly used on em-
bankment fills is as follows. c. Construction of a test fill should be very strict,
otherwise data obtained may be of questionable value.
a. Crawler and rubber-tired tractors and bulldozers. Plans and specifications for the test fill are prepared by the
This equipment is used to tow compactors, plows, harrows, design engineer to evaluate construction procedures and
etc., with bulldozer blades to move and spread material and material behavior so that results of the test fill can be used
to remove oversize stones from embankment fill. in design and construction of the prototype; therefore,
changes or additions should not be made without approval
b. Motor graders (road patrols). Graders are used to of the design engineer.
spread and mix material, dress up boundaries between
different zones (such as core, transition and filter), work out d. Records and data required should be established by
oversize stones, and scarify surfaces of previously com- the design office; records should be kept up to date, and
pacted lifts. data plotted daily, as changes in the test program may be
necessary to obtain desired information. It is important to
c. Disks. Disks are typically towed by rubber-tired or record any and all observations made by field personnel, no
crawler tractors (Figure 5-4) and used to scarify surfaces of matter how insignificant they may seem at the time.
previously compacted lifts or to aerate and blend water into Photographs and notes or visual observations are extremely
uncompacted lifts before compaction. important, as they often provide answers to perplexing
questions that would otherwise go unanswered.
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Specifications:
Towed:
Double-drum unit: Water or sand and water ballasted. Towed by crawler or rubber-tired tractor at not more than
5 mph.
Weight: Weighted: at least 4,000 lb/ft of drum length. Empty: not more than 2,500 lb/ft of drum length.
Feet: Uniformly spaced. Approximately three feet per each 2 sq ft of drum surface. Foot length: 9
to 11 in. Face area: 7 to 10 sq in.
Self-propelled: May be used in lieu of towed roller if it causes no shearing of or laminations in fill.
Specifications same as above except that (a) empty weight greater than 2,000 lb/ft of drum
length may be used with face areas of feet not greater than 14 sq in. to approximate nominal
foot pressure of towed roller, (b) inflation pressures of rubber-tired front wheels not greater
than 40 psi. Speed not greater than 5 mph.
Use: To compact fine-grained soils or coarse-grained soils with appreciable plastic fines.
Advantages: Kneading, churning, and tamping action mixes soil and water better than other compaction
equipment (this does not preclude proper processing of material prior to compaction, however);
produces good bond between lifts; and breaks down weak rock or cemented soils.
Disadvantages: Leaves surface rough and loose, and therefore susceptible to wetting by rains or surface
waters. Compacts to shallower depth than other equipment. Effectiveness diminished in
compacting soils containing cobbles or large rock fragments. Self-propelled rollers sometimes
cause shearing of or laminations in fill.
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RUBBER-TIRED ROLLER
Specifications:
Wheels: Minimum of 4 wheels abreast, each carrying equal load in traversing uneven surfaces.
Wheel spacing: Distance between nearest edges of adjacent tires not to exceed one-half of tire width under
25,000-lb wheel load. Tire pressure 80 to 100 psi.
Weight: Ballast loading to provide wheel loads from 18,000 to 25,000 lb.
Advantages: Compacts to greater depths than sheepsfoot roller. Produces relatively smooth compacted
surface which is rain-resistant. Effective in compacting in closer quarters than sheepsfoot (i.e.,
against rock abutments and concrete structures). More effective than sheepsfoot in
compacting cohesive soils containing large particle sizes. Wet areas of fill can be determined
by observation of roller rutting.
Disadvantages: Compacted surfaces must be scarified before placing next lift. Not as effective as sheepsfoot
roller in breaking down soft rock or in mixing fill material.
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Specifications:
Single drum unit. Towed by crawler tractor with minimum drawbar horsepower of 50 at speed not to exceed 1.5 mph (when
compacting rock fill or sands and gravels), or self-propelled at speed not to exceed 1.5 mph (when compacting sands and
gravels only).
Weight: Minimum total weight, 20,000 lb; 90 percent transmitted to ground by smooth drum with roller
in level position attached to towing vehicle. Unsprung weight of drum shaft and internal
mechanism not less than 12,000 lb. (Note: while guide specification CW 02212 specifies a
roller with a minimum static weight of 20,000 lb, lighter rollers (7,000 to 10,000 lb) have been
effectively used to compact pervious sand and/or gravel, and to compact soft rock that would
be broken down too much by heavier rollers.)
Vibration: Frequency: between 1,100 and 1,500 vpm. Dynamic force: not less than 40,000 lb at
1,400 vpm.
Advantages: Greater densities can be obtained in cohesionless soils than with tamping or rubber-tired
equipment. Fill may be flooded with water to improve compaction.
Disadvantages: May cause degradation of soil or rock-fill particles and create layers of fines.
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Test fills for earth embankments are often necessary to Impervious materials include clays of high and low plas-
establish proper loose lift thicknesses and the number of ticity (CH and CL), clayey sand or gravel (SC and GC), and
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Figure 5-6. Test fill data from Canyon Dam, Texas 5-8. Compaction Specifications
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EM 1110-2-1911
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c. Uncompacted or loose lift thickness will be specified. recompacted. If the minimum density is not obtained even
Lift thickness specified will be based on type of material though the water content is within the specified limits,
and compacting equipment used. Impervious or semi- additional roller passes at Government expense will be
pervious materials are commonly placed in 6-to-8-in. loose required. Procedures for performing tests to determine field
lift thicknesses and compacted with six to eight passes of a densities and water contents are contained in para-
sheepsfoot roller or in 9-to-12-in. loose lift thicknesses and graph 5-10, and application of these tests to compaction
compacted with four coverages or a 50-ton rubber-tired control is included in Appendix B.
roller. When using a rubber-tired roller or any roller that
leaves a smooth surface after compaction, scarification of 5-9. Simple Control Procedures
the compacted lift prior to placing the next lift is specified
to ensure a good bond between the lifts. In confined areas a. Simple controls using both visual observations and
where hand-operated power tampers must be used, fill is rough measurements are the primary means by which con-
commonly place in 4-in. loose lifts and compacted to struction control is carried out. However, they must not be
densities achieved with sheepsfoot or pneumatic-tired used as the only means of control, but must be supple-
equipment under the above-mentioned conditions. mented by an extensive program of control testing. For any
estimate to be meaningful and accurate, the observer must
d. In-place water content and density must be related to have his eye and hand calibrated to all conditions expected.
optimum water content and to maximum dry density to It is desirable to construct a small test section prior to the
judge whether a compacted soil is suitable or unsuitable. beginning of major fill placement so inspectors and the
Minimum acceptable field density is normally established in contractor can become familiar with the behavior and
design as a percent (usually 95 or above) of maximum dry compaction characteristics of the fill material and with the
density1, and an allowable range of placement water performance of the compacting equipment. Noncritical
contents is given in the specifications relative to optimum locations are often used for such experimentation, such as
water content of the soil being compacted. Each soil type in reaches where embankment heights are low.
has a different maximum dry density and optimum water
content for a given compactive effort, and it is necessary b. An inspector should be familiar enough with the
that in-place field densities and water contents be compared materials at a job site to recognize when the soils are too
with laboratory-determined optimum water contents and dry, too wet, or at optimum water content. To gain needed
maximum densities of the same soil. Because mixing familiarity with site materials, an inspector should spend
different soil strata in borrow areas can result in materials time in the field laboratory performing compaction tests and
with unexpected compaction characteristics, if a material index tests such as Atterberg limits so as to become familiar
being compacted in the field cannot be related to available with differences in appearance and behavior of site fill
laboratory compaction data, a laboratory compaction test materials.
should be performed on that material. Check companion
tests should be performed by field personnel before fill c. A trained inspector should be able to pick up a
placement to ensure consistency with target values for a handful of soil and make a reasonable estimate of its water
given soil. content relative to optimum by feel and appearance.
Experienced inspectors can often estimate deviation from
e. Assumptions are made in design regarding shear optimum water content to within 1 percent. Material may
strength, permeability, and deformation characteristics of the be examined by rolling a small amount on a clipboard or
embankment fill. These properties vary with density and between the hands to get an indication of how close to the
water content of the compacted soil. Therefore, soil must plastic limit the soil is. Comparison with the plastic limit is
be placed as specified; otherwise, design assumptions are a good rule-of-thumb because there is often good
not met and problems may occur in the completed structure. correspondence between optimum water content and the
Thus, desired density and placement water content range are plastic limit of a soil. However, after the inspector has
not arbitrarily established but are specified for very definite made visual and contact examination, a water content test
reasons, and both requirements must be satisfied. If the should be performed on the material in question for
water content is outside its specified range, even though the confirmation of water content.
desired density is obtained, the soil must be reworked and
d. In addition to having a feel for how a soil looks and
feels when it is at the proper density, a penetration
1
When the compaction procedures are set forth in the specifications, the resistance index test is often devised by inspectors. The
percentage of maximum dry density is not specified, but the desired value resistance index test itself can range from the use of a
is given to field inspection forces by the design office.
Proctor needle (Proctor penetrometer) to that of a common
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EM 1110-2-1911
30 Sep 95
spade. Many inspectors, in fact, have had success in g. At a proper water content there will always be a
judging density by noticing the resistance of the compacted noticeable “springing” of the embankment surface as it
soil to penetration by a spade. reacts to the passage of any heavy construction equipment;
the amount will depend largely on soil type. However, a
e. Proper lift thickness is fairly easy to estimate when sudden sinking or rising of the surface under the weight of
the inspector’s judgement has been calibrated by actual the passing equipment is a good indication that a soft layer
thickness measurements. However, many contractors are or pocket exists below the surface; if there is no spring at
interested in placing lifts as thick as they can get by with, all, it is probable that several lifts of fill have been placed
and conflict often arises on this point. Therefore, control of too dry. If such a condition is noticed, it should be checked
lift thickness by visual observation alone is not sufficient by the laboratory and the condition corrected if the
and must be supplemented with measurements. Contractor underlying layers do not meet specifications.
behavior dictates the level of force that must be exercised to
maintain proper lift thicknesses. As a minimum practice by 5-10. Field Control Testing and Sampling
the inspector, it is necessary to make measurements on the
same point on the construction surface after every few a. General. Field control testing (field density tests)
layers. and record sampling of compacted fill are conducted for two
basic reasons: to ensure compliance with design require-
f. Much useful information can be gained by observing ments, and to furnish a permanent record of as-built
the action of compacting and heavy hauling equipment on conditions of the embankment. Field control testing consists
the construction surface. If the water content of the fill largely of determinations of the water content, density, and
material is uniform and the lift thickness is not too great, classification of the field-compacted material. Record
the action of the roller will indicate whether water content sampling consists of obtaining undisturbed samples (often
of the material is satisfactory and good compaction is being with companion disturbed bag samples) at selected locations
obtained. For example, it is likely that soil-water content is in the embankment during construction.
too high if on the first pass of a rubber-tired roller the tires
sink to a depth greater than or equal to half the tire width, b. Field density testing and record sample programs.
after several passes, excessive rutting of the soil surface is
observed, the surface ahead of the roller shows signs of (1) Frequent control tests should be performed at the
weaving or undulating (as opposed to “springing”). It start of fill placement; after rolling requirements have been
should be noted that the characteristics just described may firmly established and inspection personnel have become
sometimes be caused by tire pressure which is too high, but familiar with material behavior and acceptable compaction
in most instances they are caused by water content which is procedures, the amount of testing can be reduced. Many
too great. On the other hand, if the roller tracks only vary factors influence the frequency and location of control tests
slightly or not at all and leave the surface hard and stiff and record samples. Frequency of testing will depend on
after several passes, the soil is probably too dry. For most the type of material and how critical the fill being com-
soils with the proper water content, the roller will track pacted is relative to the overall job (for example, an
nicely on the first pass and wheels will embed 3 to 4 in.; impervious core will naturally require more control than will
there should always be some penetration into soil at its a random berm). Sampling should be carried out at loca-
proper water content, although penetration will decrease as tions representative of the area being checked. It is vitally
the number of passes increases. After several passes of a important in control tests that soil specimens be properly
sheepsfoot roller, the roller should start walking out of the sized; specimens that are too small yield inaccurate and
fill if adequate and efficient compaction is being obtained. misleading results. Guidance regarding proper specimen
Walking out means that the roller begins bearing on the soil sizing is given in EM 1110-2-1906 and by Gilbert (1990).
through its feet with the drum riding a few inches above the
soil surface. If the roller walks out after only a few passes, (2) A systematic testing and sampling plan should be
the soil is likely too dry. If the roller does not walk out but established at the beginning of the job. Control tests are
continues churning up the material after the desired number usually designated as routine and are performed at desig-
of passes, either the soil is too wet or foot contact pressure nated locations, no matter how smoothly the compaction
is too high. Another significant observation during operations are being accomplished. A routine control test
compaction by sheepsfoot roller is whether or not the feet should be performed for every 1,000 to 3,000 cu yd of
are coming out clean. Soil is generally too wet when large compacted material and even more frequently in narrow
amounts of material are being picked up by the feet and embankment sections where only a small volume of material
knocked off by the cleaning teeth. If soil is at the proper raises the section height considerably. In the first lift above
water content, only a small amount of sticking should occur. the foundation, tests should be made more frequently to
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EM 1110-2-1911
30 Sep 95
ensure that proper construction is attained in this important measuring a characteristic of the material that has been
area. The locations of record samples should be at the previously correlated with density and/or water content. As
discretion of the design engineer and should also be stated a rule, field density tests should be taken one lift thickness
on a predetermined plan of testing. A rough guide for deep.
taking record samples is one for every 30,000 cu yd of core
fill and every 30,000 to 50,000 cu yd of compacted material (1) Direct methods.
outside the core. Since the record samples are taken pri-
marily to determine the shear strength of the fill, it may be (a) Direct methods of measuring volume include sand
more important in many dams to concentrate more tests in displacement, water balloon, drive cylinder, piston sampler,
the material outside the core because this is where a major and water displacement. Apparatus, procedures, and guid-
portion of the resistance to sliding is developed. For dams ance in obtaining satisfactory results for the sand dis-
with narrow central plastic clay cores placed wet of placement, water balloon, drive cylinder, and piston sampler
optimum water content for impermeability and flexibility, are given in EM 1110-2-1907. The sand displacement and
flanked by large lean clay zones, record samples should be water balloon methods are the most widely used for
taken mainly in the clay shells. measuring in-place density because of their applicability to
a wide range of material types and good past performance
(3) In addition to routine control tests, tests should be records. Apparatus for these two methods is shown in
made in the following areas: where the inspector has reason Figure 5-7. Sand displacement is the most reliable and most
to doubt the adequacy of the compaction, where the frequently used method; it should be the referee test for all
contractor is concentrating fill operations over relatively other control methods. The drive cylinder and piston
small areas, where special compaction procedures are being sampler are good for obtaining samples from which the
used (power tampers in confined areas, etc.), where density can be ascertained, but are limited to moist fine-
instruments are located, and adjacent to abutments. grained cohesive soils containing little or no gravel and
moist fine sands that exhibit apparent cohesion. The water
c. Record samples. Undisturbed record samples may be displacement method is generally used for testing gravelly
obtained by carefully carving out about a cubic foot block soils where holes as large as one cubic yard are needed to
of the compacted fill. The sample is then sealed in wax and obtain accurate results. A water-displacement density test
encased in a wooden box or protected by other methods of is shown in Figure 5-8. A thin plastic sheet is necessary to
packaging against disturbance or water loss. Undisturbed line the hole to prevent leakage, and special equipment is
record samples are also taken by trimming around a large often required for handling and weighing the large volume
steel cylinder as it is pushed into the fill (e.g., the Fort of excavated material and measuring the large volume of
Worth district has used a sampler 7-1/2 in. in diam by 10 in. water. A 3-to-5-ft-diam steel ring with a height about equal
high). Details for obtaining and preserving record samples to the compacted lift thickness is often used where the fill
are described in EM 1110-2-1907. Undisturbed record surface is rough and uneven. The volume of water required
samples are subjected to shear and perhaps consolidation to fill the ring with the plastic liner in place is determined,
testing by the division laboratory, and the material from the water and liner removed, and then the hole is dug with-
trimmings and unused portions of the record samples or of out moving the ring. The liner is then placed in the hole,
the companion bag samples are used for laboratory and the volume of water required to fill the hole to the top
compaction, gradation, specific gravity, Atterberg limits, and of the ring is determined. The difference between the two
other laboratory tests. Undisturbed record samples and bag volume measurements is the in-place volume of excavated
samples must be tested promptly if the results are to be fill material. Apparatus and procedures for large volume
useful in construction control. water displacement tests are described by Hammer and
Torrey (1973) and by Gordon and Miller (1966).
d. Field density tests. Field density determination
consists of volume and weight measurements to determine (b) Water content measurement is required to control
wet density of in-place fill and water content measurement placement water content and to determine dry density for
to determine fill water content and dry density. Volume and field tests. Methods for direct water content determination
weight measurement can be determined by direct or indirect include conventional oven drying, hot plate or open flame
methods. In direct measurements, weight of the material drying, drying by forced air, and drying in a microwave
removed from a hole in the fill and hole volume are used to oven. In conventional oven drying, a soil specimen is dried
determine wet density. Direct water content determination to a constant weight in an oven maintained at a temperature
involves drying the soil in an oven at 110 ± 5 °C, then of 110 ± 5 °C and the weight loss determined. Convention-
weighing the dry soil to determine water loss. Determining al oven drying is the standard for accuracy in water content
density and water content by indirect methods involves measurement; details of the test are described in EM 1110-
5-9
EM 1110-2-1911
30 Sep 95
5-10
EM 1110-2-1911
30 Sep 95
5-11
EM 1110-2-1911
30 Sep 95
careful calibration using soils of known density and water minimized. The backscatter method avoids the need
content and considerable operating experience. Even then to create an access hole in the compacted soil
the results may be questionable due to the significant because the unit rests on the surface. The air-gap
influence of nonuniform water content or variation due to method (shown in Figure 5-11c) raises the device
the influence a small piece of gravel can have on the above the surface to lessen composition error, but
penetration resistance. The Proctor penetrometer is, accuracy will still not match that of the direct
therefore, not recommended for general use in compaction transmission method. Moisture measurements utilize
control; it can be a very useful tool in supplementing the a method based on the principle of measuring the
inspector’s visual observations and providing a general slowing of neutrons emitted into the soil from a fast
guide for detecting areas of doubtful compaction. The neutron source, usually using the backscatter method.
procedure for determining the relation between wet unit Generally, the density and water content measuring
weight, penetration resistance, and water content is devices are incorporated into a single self-contained
described in the ASTM Standards, Designation D 1558-63. unit. Both surface-type nuclear gauges, which test
materials at depths greater than 1 ft, are now
(b) Nuclear method. available. Descriptions of gauges available from a
number of manufacturers are given by Smith (1968).
• The nuclear method is an expedient means by which Modern nuclear gauges contain a microcomputer
both water content and density determinations can be which processes gauge readings to directly calculate
made more rapidly than by conventional direct and display wet density, dry density, degree of
methods. Improvements in the design of nuclear compaction, and water content.
equipment and a better understanding of the nuclear
principles have led to increasingly widespread use of • No license is required by the Atomic Energy
nuclear gauges. The nuclear method is not permitted Commission (AEC) for using nuclear gauges when
as a primary control, but is used to supplement direct the radiation-emitting source is a naturally occurring
methods. A 1969 survey of Corps of Engineers use radioactive nuclide. A license is needed when the
of nuclear gauges showed 13 Corps offices were radiation-emitting source is a by-product radioactive
using such instruments in various applications. A nuclide. All Corps applications for AEC licenses,
1990 survey of nuclear density gauge use in renewals, amendments, and correspondence thereto
earthwork construction within the Corps showed that must be forwarded through normal Corps channels to
seven districts were using nuclear instruments to HQDA (CESO-ZA), Washington, DC 20314, for
supplement other methods of density and water processing. AEC standards are contained in Title 10,
content determination. Guidance given by Webster Part 20, Code of Federal Regulations (Atomic Ener-
(1974) and by Rosser and Webster (1969) requires gy Commission 1966). Full time radiation inspectors
that before a nuclear density gauge is used on a with special training must be present on Corps
Corps of Engineers job, results obtained using projects where nuclear gauges are used. This
factory curves must be compared with density and requirement can be a barrier on small jobs or jobs
water contents determined by conventional methods. with marginal funding.
Based on this comparison, corrections may be
required to the factory curve or a new calibration • The advantage of the nuclear method is the speed
curve may have to be developed. It should be noted with which density and water content determinations
here that recent research has shown that the can be obtained as compared with conventional
calibration of nuclear gauges is highly nonlinear in methods. An in situ density and water content deter-
determination of water content or soil density at mination can be made in approximately 15 min as
water contents greater than about 40 percent, and compared with a period as long as 24 hr for conven-
steps should be taken to account for this nonlinearity. tional methods when oven drying is used. In
addition, the possibility of human error is minimized.
• Most nuclear gauges are built to measure density by However, the field density and water content must
one or more methods, classified as the direct trans- still be related to a compaction curve or to maximum
mission, backscatter, and air-gap density methods as and minimum densities, as is the case with data
shown in the schematics of Figure 5-11; however, all obtained by conventional methods. Consequently, it
nuclear gauge methods are based on the principle of is necessary to obtain a sample of the material at the
using gamma radiation to establish a density rela- location of the nuclear test in order to relate the field
tionship. The direct transmission method is reported and laboratory date.
to yield the best accuracy, in that material
composition and surface roughness influences are
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EM 1110-2-1911
30 Sep 95
• The operating principle of the nuclear moisture energy primarily by colliding with chemically bound
gauge is, very basically, that neutrons from a hydrogen present in the (soil-water) medium, and
radioactive source are released into a soil/water neutrons are absorbed by certain elements which may
mixture then detected some distance away after they be present in the soil. Therefore, some of the factors
have traveled through the soil. The (initial) that adversely affect water content measurement
statistical energy spectrum of the released neutrons using this procedure may be more clearly visualized:
is known; after reacting with the soil/water medium (1) All chemically bound hydrogen causes neutron
for a period of time, the neutrons reach a state of energy loss, including that in organic matter,
energy equilibrium which is detected and measured adsorbed water, and structurally bound water as well
by a probe. Detected energy level is then related to as “free” water. Only free water should be included
soil water content through calibration. Neutrons lose in a normal water content determination; the gauge
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EM 1110-2-1911
30 Sep 95
cannot discriminate between hydrogen in free water f. Methods of relating fill density and water content to
and hydrogen in other sources. (2) Certain elements maximum density and optimum water content.
(such as iron, potassium, manganese, boron, and
chlorine) are highly absorptive of neutrons. The (1) The fill density and water content must be related to
presence of these elements in soils will cause laboratory values of maximum density and optimum water
erroneous water content determination using a content of the same material in terms of percent compaction
nuclear gauge. Because of the possible presence of and variation of fill water content from optimum. For this
generally unknown quantities of organic matter, comparison to be meaningful, valid laboratory values must
adsorbed water, structurally bound water, and highly be selected.
absorptive elements, water content measured by the
nuclear gauge must be frequently checked against (2) Performance of the standard five-point compaction
that determined in the conventional oven to account test on the field density test material is ideal, as it gives the
for the factors which are known to influence nuclear correct values of maximum dry density and optimum water
gauge results. In addition, nuclear gauges react with content directly. However, the five-point test is time-
and are affected by other nuclear gauges in close consuming and generally not possible on material from each
proximity; therefore, a nuclear gauge should not be field density test.
used within 30 to 40 ft of another nuclear gauge in
use in the field. A major disadvantage of nuclear (3) There are other, less time-consuming methods based
gauges is that specimen size is unknown and can on identification of the field density material with one of the
never be established with certainty; the volume soils on which standard compaction tests have been per-
“probed” by a nuclear gauge is determined by water formed in connection with design studies and during
content, soil mineralogy, grain-size distribution, and construction. The means of identification are as follows:
geometry of the test configuration (for example,
results determined in a narrow utility trench may be (a) Two-point compaction test.
in considerable error relative to results obtained on
a flat, obstruction-free soil surface). (b) One-point compaction test.
• Additional disadvantages of nuclear methods for (c) U.S. Bureau of Reclamation (USBR) rapid
determining field densities and water contents are compaction control.
general lack of understanding of the method as well
as factors affecting the results and, consequently, (d) Atterberg limits correlations.
lack of confidence in the results; calibration curves
must be developed and/or verified by field tests for (e) Grain-size distribution correlation (sometimes used
each instrument; and although the proper use of for coarse-grained soils).
nuclear gauges presents no health hazards, rigid
safety regulations and documentation requirements (f) Visual comparison.
must be met. For this last reason, field parties are
sometimes reluctant to use nuclear equipment. These methods are discussed in detail in Appendix B. The
two-point and one-point methods follow essentially the same
e. Test pits. It is sometimes desirable to excavate deep procedure as the five-point method, but are quicker since
test pits to determine the overall condition of the compacted fewer points need to be run. It should be noted that the
embankment. Field density tests can be made and un- five-point method requires wetted soil cured overnight prior
disturbed record samples can be obtained at various to compaction to allow uniform distribution of added water.
elevations as the pit is being dug, and the degree of In the one- and two-point methods, whether adding water to
uniformity or water content with depth can be obtained by or drying back the fill material, thorough mixing is required
testing samples at frequent depths. An important advantage to obtain valid results. Water contents and dry densities
of the test pit is that it allows a visual inspection of the from the one- and two-point methods are plotted on the
compacted fill; soft spots can be detected, and it can be same plot as the five-point laboratory compaction curves
determined whether or not successful bonding of the fill lifts used for control. The curve best fitting the plotted points is
has been accomplished. Large-diameter bucket auger holes selected, and the field values are compared with the
(30 to 36 in.) can also be utilized effectively for this maximum density and optimum water content of that curve.
purpose. All tests and visual observations should be Atterberg limits correlations are based on correlations of
thoroughly documented, including numerous photographs. liquid limit, plastic limit, or plasticity index with optimum
Test pits must be backfilled with properly compacted soil. water content and maximum dry density. In the USBR
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EM 1110-2-1911
30 Sep 95
rapid method, a wet density compaction curve is developed 5-11. Operations in Adverse Weather
from three wet density compaction points, and the percent
of maximum dry density and deviation from optimum water a. Cold weather.
content are computed without having to perform water
content tests. The visual method consists of establishing by (1) Research (Sherards et al. 1963) has shown that good
visual examination that the field density material is the same compaction is not obtained on frozen soil or on soil at
as one of the materials on which laboratory compaction temperatures near freezing. Contractors will often want to
curves were developed. It is a frequently used method, but keep working as long as possible in cold weather, and the
is the least desirable because materials that look very much Resident Engineer may be faced with a difficult problem in
alike and have the same soil classification can have widely deciding exactly when it becomes too cold for further fill
varying compaction characteristics. placement. There are no definite criteria for establishing the
temperature below which satisfactory work is impossible.
g. Procedures for gravelly soils. Results of the five- The rate at which unfrozen soil loses heat and freezes
point, two-point, one-point, and visual methods are usually depends on the size of the construction surface and the rate
correlated directly with field density test results if of fill placement. In cold weather it is important to keep
appropriately sized compaction molds are used (see the construction surface “active,” i.e., fill placement must
EM 1110-2-1906). However, the Atterberg limits correla- continue without lengthy interruptions. Work has been
tions and USBR rapid methods are based on the minus continued at some dam sites in 20 to 30 °F weather 24 hr a
No. 4 sieve fraction; consequently, the field density test day, 7 days a week to keep the construction surface active.
results must be corrected to obtain the water content and Work must be terminated whenever water in the soil freezes
density of the minus No. 4 fraction. Corrections must also quickly and equipment operation becomes awkward. Under-
be applied to the field results if the laboratory compaction water dumping in water with floating ice should not be
curve is based on a scalped material (corrections would not allowed because of the possibility of entrapping ice in the
be made if particles larger than 2 in. are replaced with an fill. Construction in cold weather must be limited to special
equal weight of particles from 2 in. to the No. 4 sieve and situations and always performed under close observation
tested in the laboratory in a 12-in. compaction mold). The with extreme care.
equations necessary to make these corrections and proce-
dures for applying them are given in Appendix B. (2) Protecting the construction surface during the winter
when operations are shut down is another problem. The
h. Evaluation of test results and subsequent actions to degree of protection required depends on the severity of the
be taken. As soon as field test results are obtained, they winter. In most parts of the United States, it is not
must be compared to appropriate values of maximum dry necessary to use any protection if the embankment surface
density and optimum water content to determine if specifi- has been properly seal-rolled; the worst damage is a heaving
cation requirements have been met. If measured values and loosening of the upper few inches of the embankment
match or exceed specification requirements, the next lift can fill by frost action. Before construction starts again in the
be added. If test results show that specifications have not spring, the surface material should be excavated to a depth
been met, corrective measures must be taken immediately. below the line of frost action. The depth at which to
A lift must be rejected if the material is too wet or too dry. excavate is best determined by visual examination of
If density is too low but water content is acceptable, addi- shallow test holes. In colder climates where the embank-
tional rolling is all that is required. If, however, water ment freezes to a depth of several feet, it may be desirable
content is outside specifications, the entire lift should be to protect the construction surface during winter with several
reworked and rerolled. A lift that is too wet should be feet of loose material. Other methods of protection have
worked by disking until the water content is lowered to an been used in extremely cold areas, such as ponding water
acceptable value and then recompacted. A lift that is too over the construction surface and even using some type of
dry should be disked, sprinkled, and redisked until the heating coils on foundations for structures (spillway, outlet
additional water is uniformly distributed, then recompacted. works tower, etc.).
It is important when reworking a rejected lift that the full
lift depth be reworked, not just the upper portion. All b. Wet weather.
reworked lifts should be retested for density and water
content. It is desirable to determine the reason(s) for an (1) Maintaining proper water content during periods of
unsatisfactory lift in either borrow or fill operations, so that high precipitation is always a problem. Impervious
conditions causing the problem may be corrected on future materials should never be placed on embankments during
lifts. rain, although construction operations can often be continued
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EM 1110-2-1911
30 Sep 95
successfully between rains. Water content of material is very difficult to obtain uniform water content distribution
spread on embankments can be reduced somewhat during in plastic clays containing lumps without a “curing” period
periods between rains by plowing or disking before rolling. of a few days; this is, of course, not practical on the
embankment surface. Consequently, disking followed by
(2) It is desirable to compact fill material as soon as addition of water and then thorough mixing with a heavy
possible after spreading to minimize the time loose fill is rotary pulverizer may be required to obtain uniform
exposed to precipitation. Rubber-tired rollers are superior distribution of water in such soils.
to sheepsfoot rollers when rains are frequent because they
leave a relatively smooth compacted surface, whereas the 5-12. Compaction in Confined Areas
sheepsfoot roller leaves a loose rough surface that readily
soaks up rain water. If a sheepsfoot roller is used for a. Confined areas are those where normal rolling
general compaction, smooth-wheel rollers (steel or rubber) operations with heavy equipment are restricted or where
can be employed to seal the surface when rain is imminent. heavy equipment cannot be used at all and hand compactors
In any event, the construction surface should be kept sloped must be used. Compaction with hand compactors should be
to allow the water to run off instead of standing in puddles avoided and heavy equipment used in these areas if at all
and soaking in. After a rain, if some ponding does occur, possible. Confined areas, where heavy equipment can often
it is usually easy for the contractor to install a few small be used on a careful basis if maneuvering room is available,
ditches to drain these areas. include fairly smooth abutments (rock or earth), conduit
barrels, towers, etc. Confined areas where hand compactors
(3) It is often necessary after a rain to scarify and work often must be employed are adjacent to thin concrete
the construction surface to a depth below that of excessive structures, such as wing walls, guide walls, etc., where
moisture penetration until it is dried to a satisfactory water heavy equipment might damage the structure; adjacent to
content or, to remove and waste all affected material. If rough, irregular rock abutment slopes where heavy equip-
procedures to facilitate runoff are followed (sloping the ment cannot get in close enough to the surface to squeeze
surface, sealing the surface with smooth rollers, etc.), the the fill into all the irregularities and openings in the rock;
depth of moisture penetration will be kept to a minimum. and around seep rings or plugs where maneuverability is a
problem.
c. Dry weather.
(1) Heavy equipment. When conditions are such that
(1) If material being dumped on the fill is too dry for heavy compaction equipment can be used to compact the
proper compaction, water must be added by sprinkling after soil against rock abutments or walls of concrete structures,
it is spread and before it is rolled. The amount of water the construction surface of the embankment should be
added and the blending required will depend on grain size sloped at about 1V on 6H for a distance of 8 to 12 ft away
and plasticity of the soil, fine-grained soils of high plasticity from the rock or concrete. This will allow the roller to act
requiring the greatest amount of blending. Soil must be more directly in compacting the soil against the abutment or
worked with disks to thoroughly blend and homogenize structure. The area can then be rolled perpendicular to the
added water into the soil. The importance of uniform face of the abutment or structure by heavy pneumatic
moisture distribution cannot be overemphasized; if pockets equipment or a sheepsfoot roller or by heavy pneumatic
of wet and dry soil are allowed in uncompacted material, equipment in a direction parallel to the face.
very poor compaction will result.
(2) Hand compactors. If heavy rollers cannot be used in
(2) Sprinkling the soil can be accomplished by hosing this manner, the roller should be allowed to work as close
from a pipeline, located along either the embankment toe or as possible, and the portion of embankment directly against
the crest, or by the use of water trucks. The latter method the rock or concrete should be compacted with smaller
is the most effective and the most commonly used today. equipment in thinner lifts. Smaller equipment refers to
Pressure sprinkling systems on trucks are superior to gravity hand-operated power tampers, as shown in Figure 5-12, or
systems and should be employed if at all possible. Water power tampers mounted on small tractors. These tampers
sprays must not be directed on the soil with such force as to are usually gasoline-operated or operate on compressed air.
cause fines to be washed out. Until the inspectors and Hand-operated power tampers (sometimes called rammer
contractor personnel have gained a “feel” for the amount of compactors) are probably the most widely used equipment
water needed, rough computations of the number of gallons for compacting fine-grained soils in confined areas. A loose
to add for a given area should be made, and water applied lift thickness of not more than 4 in. should be employed in
accordingly. After a few trials, a feel for the proper amount conjunction with these power tampers. Hand compactors
will develop. The coarser and less plastic the soil, the more should have a minimum static weight of 100 lb, and the
easily water can be added and worked uniformly into it. It
5-16
EM 1110-2-1911
30 Sep 95
1
5-13. Definition Outer embankment zones of some dams composed of coarse-grained soils
containing appreciable amounts of fines (i.e., greater than 5 percent) are
sometimes designated as “pervious zones.” The compaction equipment,
Pervious fill material as used in this manual is defined as
procedures, and control for materials comprising the pervious zones referred
free-draining cohesionless sand and/or gravel, containing to here are those presented in Section III on impervious and semipervious
less than approximately 5 percent passing the No. 200 fill.
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30 Sep 95
5-16. Water Content Control 5-17. Lift Thicknesses and Number of Passes or
Coverages
Water content control is unnecessary in gravel, and the
material may simply be compacted in its as-received These will be established in the specifications. Pervious fill
condition. If the material is sand or contains a significant is commonly placed in 6- to 15-in. lifts when it is to be
proportion of sand sizes, the material must be maintained in compacted by three or four passes of a vibratory steel-wheel
a high degree of saturation during compaction using water roller or a 50-ton rubber-tired roller, or in 6- to 8-in. loose
trucks with pressure spray bars, hoses connected to header lifts when it is to be compacted by three to six coverages by
pipes laid along the embankment, or other approved a crawler tractor. A note of clarification is necessary here.
methods of water application. If pervious sand is Guide Specification CE-1306 calls for a specified number of
compacted at a low degree of saturation (with insufficient “complete passes” of a rubber-tired roller or a vibratory
water), surface tension between the water present and the steel-wheel roller, where a “complete pass” is defined to be
sand grains will cause the moist soil to “bulk,” and in this complete areal coverage of the lift. This concept does not
state it will not densify efficiently under an applied retain the same meaning in a crawler tractor where the
compactive effort; the result will be a poorly compacted tracks (because of their wide separation) do not make com-
weak layer which may cause problems. It is therefore plete areal coverage of the lift. Therefore, when compaction
imperative that sand be in a high degree of saturation as the by a crawler tractor is specified, the specification should
roller passes over it, but it is often difficult to achieve a require coverages by the tracks of the tractor. In confined
high degree of saturation because surface tension will also areas where small vibratory rollers or hand-operated
prevent water from flowing freely through sandy soils. vibrating compactors are required, material is normally
Figure 5-14 shows the unique wetting system used to placed in 2- to 3-in.-thick layers with vibratory compaction
saturate the sand for the vertical sand drain at DeGray Dam. applied until densities comparable to those required for areas
The entire spray system was attached to the frame of the compacted with heavy equipment are achieved.
vibratory roller itself. The water was fed to the system by
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30 Sep 95
5-19. Construction Control (5) The inspector should observe loading, dumping, and
spreading operations, particularly if the pervious fill is well-
a. Simple control procedures. graded material, to ensure that undesirable segregation of
particles is not occurring as a result of such operations.
(1) Checking lift thicknesses of pervious fill can be
accomplished by the simple procedures described for (6) The particular importance of horizontal and inclined
impervious and semipervious materials, except that in using drainage layers to the function of a dam, and the fact that
a shovel or rod it is often difficult to determine when the these features are so limited in thickness, justify the special
top of the underlying compacted layer is reached. This attention of inspectors to see that gradations and densities of
procedure is also not practical in fills containing large gravel the in-place filter materials meet the specifications.
particles. In some cases, it is possible to excavate a small
hole in the loose material to the top of the underlying layer, b. Gradation. Gradation tests should be performed to
which is identified by a relatively higher resistance to ensure that the material being placed is within specification
digging. limits. The number of gradation tests needed will, of
course, depend on the variability of natural pervious material
(2) The inspector must make certain that the as obtained from the borrow areas. Complete gradation
embankment is always graded so that surface waters will not tests should be performed on material for which the entire
wash fines from impervious or semipervious fill materials range of particle sizes is specified. For those materials for
into the pervious fill. During construction of earth dams, which only the percent finer than the No. 200 sieve or some
placement of filter materials for drainage layers should be other sieve is specified, the material should be soaked and
kept higher than adjacent fill containing fines in order to then washed over the No. 4 and the designated lower-limit
prevent spillage of fine-grained soil onto the pervious sieve in accordance with procedures given in EM 1110-2-
material or to reduce the washing of fine-grained soils into 1906. Gradation tests should also be performed on
the materials by surface runoff. The inspector should be compacted material especially when it is suspected that there
trained to recognize the appearance of pervious material has been contamination with fines from surface waters or
meeting specifications so that he can more easily detect, when the fill material may have been degraded by breakage
without the delay of testing, the presence of excess fines. of particles during compaction.
A good indication of excessive fines is when the hauling
and compacting equipment sinks in and causes ruts in the c. Field density testing and relative density
fill surface. This usually indicates that water applied during determinations.
compaction is not draining through the material as it should
because of clogging by excess fines. (1) The water balloon and sand volume density test
methods described in paragraph 5-10d(1) can be used to
(3) In general, a vibratory roller should push only a determine the in-place density of pervious fill. It is, of
small amount of material ahead of it and leave a smooth course, more difficult to dig holes in pervious materials.
surface behind on the first pass. If the roller sinks in and When the fill material contains high percentages of large
pushes a large amount of material in front of it, either the particles, it may be necessary to increase the volume of
frequency of vibration is not correct for the particular soil holes substantially and to line the holes with plastic film so
being compacted or the material contains too many fines. that the volume may be determined by the quantity of water
or oil needed to fill it. The nuclear density meter can be
(4) It is more difficult to judge the compacted density of used for supplementary density determinations under the
pervious material than that of fine-grained material. conditions stated in paragraph 5-10d(2)(b). The density of
5-19
EM 1110-2-1911
30 Sep 95
γd γmin γmax
Dd × × 100
γmax γmin γd
where
Figure 5-15. Correlation between density and percent
passing No. 16 sieve
γd = dry unit weight of the pervious fill in place (the in-
place density), pcf
γmin = minimum density, pcf, from laboratory tests spread between the maximum and minimum density is very
γmax = maximum density, pcf, from laboratory tests small and large errors may result.
(2) Field density determinations using the water balloon (3) Correlations such as those described above should be
or sand volume procedures should be made for every used only on materials from the particular sources for which
1,000 cu yd of pervious fill placed at the beginning of the the correlations were developed. Application to materials
job and for every 3,000 cu yd thereafter, with more frequent from other, geologically different sources may lead to
determinations desirable for testing in drainage layers. considerable error because of differences in particle shapes
These tests generally should be taken one lift thickness and degradation characteristics. The selection of maximum-
deep, especially in sands. Although the performance of minimum density values by visual comparisons of field
maximum and minimum density determinations on material density test material with samples of materials on which
from each field density test would give the most accurate maximum-minimum density determination have previously
determination of the relative density of the in-place material, been made is generally not a good procedure; small
this is frequently not feasible because of time and manpower differences in particle sizes that cannot be adequately
restrictions. Therefore, it is often advisable to attempt to detected by visual comparisons have significant effects on
develop correlations between the gradation data and the these density values.
maximum-minimum density values on materials representing
the range of gradations to be expected from the sources of 5-20. Test Results and Actions to be Taken
supply. Figure 5-15 is an example of a correlation between
the percent finer than the No. 16 sieve and the maximum- Assume, for example, that it has been established that a lift
minimum density values. Where a good correlation like this has in-place relative densities between 80 and 85 percent.
is developed, a simple determination of the percent finer A review must be made of the relative densities of all
than the No. 16 sieve is all that is needed to obtain the previous lifts to ensure that a minimum average of 85 per-
appropriate maximum-minimum density values in the in- cent relative density will be maintained if the questionable
place material. In other instances, good correlations may be lift is to be accepted. The intent of the relative density
developed between maximum-minimum density values and criteria is that the relative density of the material measured
the percent of material passing other sieve sizes or the immediately after compaction must conform to the require-
coefficient of uniformity. Correlations developed between ments stated in paragraph 5-18 without any consideration of
minimum and maximum density values can be used to increase in density caused by the placement and compaction
obtain minimum density after the performance of a of subsequent lifts.
maximum density test alone. Caution should be exercised
in using such correlations for uniform sands, since the
5-20
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30 Sep 95
5-21
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30 Sep 95
5-23. Soft Rock may require stage (or phase) construction. In a wide flat
valley, the embankment on one side of the river may be
a. The use of soft rocks in the past has been dictated by constructed to the full height under one contract, with
their availability in large quantities from required subsequent portions constructed during following years.
excavations. The main concern about these materials is Where foundations are soft, the embankment may be
their tendency to weather and soften with time when constructed to a specified elevation and further fill
exposed to air and water. However, cases in which large placement deferred for a year or more to permit dissipation
portions of embankments were composed of soft rocks have of foundation pore pressures or to achieve an adequate
shown that they can be used satisfactorily in random and degree of consolidation. In a narrow steep valley with rock
semipervious zones, attaining adequate shear strength and foundations, the entire embankment may have to be
experiencing no appreciable softening after placement. completed to a stipulated elevation by a certain date to
Where soft rocks will constitute a significant structural prevent overtopping during the flood season. The
portion of a fill, their properties and the best methods of construction schedule is developed to make maximum use
compaction should be determined by means of a test of available borrow and excavation materials, considering
embankment constructed during the design studies. river diversion requirements, foundation conditions, and
seasonal weather conditions. The contractor is responsible
b. Some types of soft rock have been compacted by for constructing the particular stage or section of
first rolling over the loose lift with a heavy tamping roller embankment within the time limit specified. The inspection
equipped with long spike or chisel-type teeth (“shell force is responsible for determining that each stage or
breaker”), and then compacting the lift with conventional section of embankment is being built in proper sequence and
tamping or rubber-tired rollers. A summary of this also that each stage or section is constructed using proper
technique is given by Bennett (1958). placement sequence. Changes in sequence or timing of
stages should not be made without approval of the design
Section VI engineer.
Semicompacted Earth Fills
5-28. Placement Sequence
5-24. Uses
a. It is usually required that the embankment be brought
Spoil berms, channel fillings, and low levees to protect up fairly uniformly over the entire width and length of the
farmlands are often constructed of semicompacted fills. section under construction. Interim embankment crests
should be crowned slightly to provide surface drainage
5-25. Specifications during wet weather. Specified transverse slopes of interim
crests may range from 1 to 5 percent. During periods of
Semicompacted fills are those specified to be compacted by dry weather, the fill heights of central impervious zones are
the routing of hauling and spreading equipment over the sometimes allowed to exceed the heights of adjacent
spread layer. Lift thickness is specified, but the range of pervious zones by as much as 5 ft to permit continuous
placement water contents is either not specified or permitted placement of impervious material. However, special
to vary widely. precautions such as sloping the impervious fill material
away from the pervious zone are required to keep
5-26. Construction Control impervious material out of inclined filter zones.
Inspection of semicompacted fill is usually entirely visual, b. Placing material in a cutoff trench should be
although a few density tests may be made for record accomplished by dumping and spreading the first lift of the
purposes. The primary concern of the inspector is to ensure downstream filter zone material (if such a filter is required
that the specified lift thickness is not exceeded, suitable at the downstream trench slope) and then dumping and
materials are being used, and hauling and spreading spreading the first lift of impervious material. This should
equipment covers the fill uniformly. be followed by compaction of both zones concurrently, with
separate equipment being used on each zone. Dumping and
Section VII spreading filter layers first will help to maintain the
Sequence of Placement and Measurement of Quantities specified width of the filter zone. A downstream horizontal
drainage zone should be completely placed and covered by
5-27. Schedule of Construction two lifts of downstream shell materials as soon as possible
to prevent contamination of the blanket by exposure to
The schedule for construction of an earth or rock-fill dam surface waters carrying fines.
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EM 1110-2-1911
30 Sep 95
5-29. Measurement of Quantities so that underlying bedding cannot be washed out, provides
excellent slope protection. Two primary factors govern
Measurement of excavated materials is usually based on successful construction and are discussed below.
cross-section surveys of the area before and after
excavation, using the average end area method for (1) Loading from the quarry to provide a good mixture
computing quantities. For embankment fill, a cross-section of different sizes within the required gradation in each load.
survey of the outer boundaries and average end area method Proper loading from the quarry requires that blasting
are used in computing quantities. For separate zones within operations produce proper sizes and that the inspector be
an embankment, the theoretical quantities are computed experienced in inspecting the loading operations.
from the lines and grades shown in the construction
drawings. Inspection personnel should be completely (2) Placing loads on the slope to provide uniform
familiar with provisions of the specifications and lines and distribution of different sizes without segregation and
grades shown on construction drawings so that instances of rearrangement of individual rocks to provide a rock mass
overexcavation or fill placement outside contract lines and without large voids. A gradation test (performed by weigh-
grades are recorded. This will assist in preventing possible ing a sufficient quantity) should be made for each 10,000 cu
errors in measurement and certification of payment for yd of placed riprap. Two ENG forms for plotting grada-
quantities in excess of contract provisions. tions curves are available. These forms are ENG Form
4055 dated April 1967, “Riprap Gradation Curves” and
Section VIII ENG Form 4056 dated April 1967, “Gradation Curves for
Slope Protection Riprap, Filter, and Bedding”. Placement should be
accomplished by placing loads along the slope against
5-30. Areas to be Protected previously placed riprap; this will reduce segregation of
sizes that would otherwise occur if loads were dumped in
Slope protection is required to protect upstream slopes separated piles. The best method of placement to avoid
against damage from wave erosion, weathering, ice damage, segregation is to use a skip as shown in Figure 5-16a.
and damage from floating debris. Upstream slope protection Dumping rock at the top of the slope into a chute should
of earth dams usually consists of riprap, although soil never be allowed since this will result in segregation. If
cement, concrete paving, and asphalt paving have been dumping is done from trucks, it is usually necessary to
occasionally used when riprap was not economically winch load haulers down the slope to the placement
justified. Dams with outer shells of sound, durable, large location. Dumping should proceed along horizontal rows
rock may not require further protection. Downstream slope and progress up the slope; loads should not be dumped to
protection is required to protect against damage from surface form rows up the slope. If very large (4 to 5 ft diam) rock
erosion by wind and rain. Downstream slope protection is specified, a crane with an orange peel attachment
includes gravel for dry climates, turf in humid climates, (Figure 5-16b) operating on a platform built up on the slope
riprap where tailwater may create wave action, and waste can be used. Other equipment such as Gradalls, cranes with
rock. Proper field construction procedures and enforcement clamshell buckets, and rubber-tired front end loaders, can be
of specifications are particularly important in obtaining slope used to place riprap. These are preferable to dumping from
protection that will remain in place and in minimizing haulers. Close visual inspection after dumping and spread-
maintenance during the life of the dam. ing is required to determine the degree of uniform
distribution of different sizes and close-knit arrangement of
5-31. Upstream Slope Protection individual pieces. Reworking, generally by hand, will
almost always be required; however, reworking can be kept
Placement of upstream slope protection may be accom- to a minimum if care is taken when loading to ensure that
plished either as the embankment is being built or after the each individual load has the proper amount of each size
embankment is completed. This depends on the elevation rock (i.e., the proper gradation). Supplemental gradation
limits of slope protection, the schedule for impounding checks might be made by the photogrid method, described
reservoir water, and the type of slope protection. The best by Curry (1964), in which a 10-ft-by-10-ft aluminum pipe
procedure is to require that the slope protection construction form containing a 1-ft-by-1-ft grid or rope is placed on the
not lag behind earth-fill construction more than 10 ft in riprap and photographed. From the photograph, the number
elevation. and size of stones visible at the surface are determined.
However, for materials that have been selectively arranged,
a. Riprap. Riprap is the most commonly specified type as by hand, this may not provide an accurate determination
of upstream slope protection. Properly graded riprap, placed of size distribution. Firm enforcement of specifications is
to provide a well-integrated mass with minimum void spaces required, especially during early stages of riprap placement
5-23
EM 1110-2-1911
30 Sep 95
5-24
EM 1110-2-1911
30 Sep 95
asphalt paving are other methods of protection for upstream (2) That the specified type, quality, and quantity of
slopes. These methods have been used infrequently, if at fertilizer and seed are used.
all, for Corps of Engineers dams in the past.
(3) That turfing operations are conducted during good
5-32. Downstream Slope Protection weather conditions, and necessary interim precautions are
taken to prevent erosion, such as mulching with hay or
a. Grass turf. Grass turf for protection of downstream burlap for a protective covering.
slopes is usually specified in humid climates for earth
embankments. Where the downstream embankment zone is b. Riprap. Riprap placed on the lower downstream
composed of pervious material, sufficient fine-grained soil slope to protect against wave action from tailwater should
or topsoil must be placed to support vegetation growth. The be controlled in the same manner as upstream riprap.
method usually specified consists of clearing the slope of Above the elevation needing such protection, dumped rock
any roots and stones, tilling to a depth of at least 4 in., (usually waste rock) is used only when readily available
fertilizing, seeding or sprigging, compacting, watering, and from required excavation or stripping operations. (Control
maintaining as required to establish the turf. Temporary or should conform with specification requirements).
permanent protection should be established on completed
portions of the embankment as soon as possible. The usual c. Gravel. Gravel or rock spalls (depending on
practice of waiting until near the end of construction and available material) are sometimes used for downstream slope
trimming slopes by filling erosion channels with loose protection. Where the outer downstream shell contains
material and then fertilizing and seeding has resulted in random granular materials, it is often specified that cobbles
continuing maintenance problems at several projects. and rocks be pushed out to the edge and used in the slope
Specifications usually provide detailed instructions with protection. In this case, it is desirable that placement of
which inspection personnel should be familiar. Frequent downstream slope protection be kept 5 to 10 ft behind
inspection should be made to ensure the following: embankment placement. The gravel or spalls are usually
dumped and spread horizontally along the outer slope to
(1) That the soil is properly tilled and not allowed to depths of at least 1 ft measured perpendicular to the surface.
migrate down the slope during tilling, which might create
depressions or undulations.
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EM 1110-2-1911
30 Sep 95
Chapter 6
Miscellaneous Construction Features
6-1
EM 1110-2-1911
30 Sep 95
significant delays would occur from a failure. Compaction or stockpiling of borrow materials for the closure section
procedures as well as other pertinent construction aspects, should be considered prior to river diversion.
including construction and surveillance requirements, would
be covered in the contract plans and specifications. In- (1) Foundation preparation and fill compaction.
spection and control testing, as outlined in Chapter 5, are Clearing, stripping, and cleaning of the foundation area in
required especially for cofferdams which will become part the closure section must be carefully inspected to ensure an
of the dam to ensure compliance with specifications or to adequate foundation. The closure section is generally the
determine when specified procedures need to be modified. highest section of the dam and is constructed to final grade
The safety of cofferdams depends to a large extent on in a much shorter time than the rest of the embankment;
competent construction. Intensive inspection is required to consequently, special emphasis on inspection and control
ensure compliance with design requirements and safe testing is justified to ensure that proper materials are placed
construction practices. A contract requirement for quality at the specified water contents and compacted to the desired
control by the contractor does not relieve resident inspection or specified densities.
forces from performing necessary and adequate inspection
and surveillance. (2) Cleaning of adjacent embankment slopes. Riprap
placed on the end slopes of completed embankment sections
(b) Slopes of temporary cofferdams depend on the type to prevent stream erosion must be removed prior to placing
of material used, degree of compaction, and their height. fill for the closure section. In addition, the end slopes must
Cofferdams are often designed on the basis of past experi- be cut back as necessary to provide unweathered and
ence. If the contractor is permitted to design a cofferdam, adequately compacted material adjacent to the closure
it should be required that an analysis of slope stability with section fill.
plans for construction be furnished. Slopes of cofferdams
designed by the Government are specified in the contract (3) Observations during construction. Because of the
drawings. rapid construction, the following problems may occur in
earth-fill closure sections:
(c) Seepage under cofferdams and through uncompacted
rock-fill cofferdams can be a serious problem unless seepage (a) High excess pore water pressures in impervious
control provisions such as a cutoff and/or an upstream zones of the embankment and in impervious foundations.
impervious zone are included. For cofferdams designed by
the Government the plans provide necessary measures for (b) Transverse cracking between the closure section and
controlling underseepage and through-seepage. However, previously completed embankment sections caused by
particular attention should be given to any contractor’s plans differential settlement.
for temporary cofferdams to ensure that adequate seepage
control measures are included. It is also important that (c) Bulging of outer slopes of largely impervious sec-
where thin upstream blankets are placed against rock-fill or tions from the use of material which is too wet.
coarse gravel, careful attention be given to providing
properly graded transitions between the impervious and The procedures for construction and criteria for compaction
coarser materials. stipulated in the plans and specifications for minimizing
these problems may include drainage layers in the
(3) Slope protection. Slope protection against wave embankment and at the contact between embankment and
action is usually not required for cofferdams. However, foundation (but never under or through an impervious core)
where a river is restricted to a channel by temporary to help dissipate pore pressures, flattening of slopes, and fill
cofferdams prior to diversion, slope protection against water contents wet of optimum to provide a more plastic fill
current action may be required. EM 1110-2-1601 should be to minimize cracking. The use of higher fill water contents
referred to for guidance on rock weights required to resist may, however, accentuate problems of bulging and high
various current velocities. pore water pressures. If potential problems are indicated,
surface movements data and piezometer readings must be
b. Closure sections. After portions of the dam have obtained daily and continuous plots maintained so that the
been constructed with the river confined to a natural or development of excessive pore water pressures and/or
constructed channel, cofferdams are constructed to divert the bulging can be detected early and corrective action taken.
river through the outlet works so that the closure section can Corrective measures taken after consultation with the design
be constructed in the dry. This may cause flooding of office may include slowing down fill placement, removal of
upstream borrow areas, in which case alternate borrow areas
6-2
EM 1110-2-1911
30 Sep 95
fill, flattening slopes, addition of stability berms, or 6-3. Surface Drainage Facilities
installation of drains.
Temporary surface drainage facilities are required to keep
6-2. Stage Construction surface runoff and slope seepage out of excavations, to
prevent contamination of filter zones by muddy runoff, to
a. Stage construction refers here to construction of an prevent saturation of loose fill before and during compac-
embankment in stages with substantial intervals of time tion, and to prevent ponding of water on compacted fill.
during which little or no fill is placed. This may be neces- Surface drainage is the responsibility of the contractor, as
sitated by environmental conditions which make the the specifications require certain phases of foundation
construction season very short or because fill placement preparation and embankment construction to be performed
must be restricted or even stopped to allow excess pore in the dry. Past field experience has shown that the
water pressure in the foundation and/or fill to dissipate. provision and maintenance of adequate drainage have
frequently been neglected, and more attention needs to be
b. Important features of construction control for stage given to them by the inspection force. Grading to direct
construction include the following: surface water away from excavations, ditching to intercept
water before it reaches an excavation or work area, provi-
(1) Review of contractor’s plans of operation as required sion of sumps to collect seepage water, and pumping from
by specifications to establish the adequacy of methods and the sumps are common means of handling surface drainage.
procedures, and field inspection to ensure that approved time The extent of needed facilities is dependent on the
schedules and construction methods and procedures are frequency, intensity, and seasonal distribution of precipi-
followed. tation. For permanent drainage facilities for roads and other
features, reference should be made to TM 5-820-4.
(2) Inspection to ensure that the surfaces of completed
sections of embankment on which additional fill will not be 6-4. Service Bridge Pier Foundations
placed for several months are sealed and/or shaped to drain
readily to prevent saturation and adequately protected Piers for service bridges to intake structures are sometimes
against erosion. constructed during early stages of embankment construction.
At several dams, lateral deformations of the embankment
(3) Inspection to ensure that outside slopes of stage- under the stresses imposed by fill placed after pier
constructed embankments that will eventually form the final construction have caused significant upstream movements of
slopes of the dam are within specified tolerances. the piers. Therefore, construction of piers should be delayed
until the embankment has been carried to near its final
(4) Observation and evaluation of piezometer and height. After construction of the piers, surveys should be
settlement data for soft foundations and consultation with made at regular intervals to monitor any movement of the
the design office to determine when fill placement can be piers no matter what steps are taken to prevent movement.
safely resumed. The design office has the responsibility to
determine when fill placement can be resumed. 6-5. Instrumentation
(5) Inspection to ensure that protective materials such as Instrumentation of earth and rock-fill dams includes
riprap, grass sodding, and trash or other debris are removed piezometers, slope indicators, settlement devices, surface
from previously completed embankment surfaces prior to movement monuments, internal vertical and horizontal
resuming fill placement. movement indicators, and seismic movement devices (see
paragraph 7-3 for required records). Seismic movement
(6) Inspection of completed embankment surfaces prior devices are described in detail in ER 1110-2-103. Various
to resuming fill placement to determine the need for types of instrumentation devices, procedures for installation,
removal of pervious surfaces materials which have become observation and maintenance, frequency of observations,
contaminated with fines or recompaction of surface materi- collection, recording, analysis, and reporting of data, and
als where water content and density are unsatisfactory. possible causes of malfunctions are discussed in EM 1110-
Field density and water content tests should be performed to 2-1908. The basic description and operating mechanism of
check visual observations. instruments generally installed in embankment dams are
6-3
EM 1110-2-1911
30 Sep 95
given in Appendix E. A comprehensive reference on geo- for recording instrumentation data and instructions for
technical instrumentation for monitoring field performance reporting them.
including calibration, use, installation, and maintenance is
given in EM 1110-2-1908. 6-6. Haul Roads, Maintenance Roads, and
Public Roads
a. Installation. Installation of instrumentation devices,
particularly electronic types, should be supervised, if not Haul roads are temporary roads built by the contractor for
actually done, by experienced personnel from within the access to work areas. Maintenance roads (or service roads)
Corps of Engineers or by firms specializing in instrumen- are temporary or permanent roads for access by Government
tation installation. The Resident Engineer staff must be forces to facilities requiring maintenance. Public roads
familiar with the planned locations of all instruments and include relocated permanent roads and roads for access to
appurtenant apparatus or structures (such as trenches for public-use facilities at the site.
piezometer lines and terminal house, etc.) so that necessary
arrangements and a schedule for installation can be made a. Haul roads. Haul roads, although usually not shown
with the contractor and/or with the office or firm that will on the plans, should be discussed in the specifications in
install the devices. Inspectors should inspect settlement general terms. The contractor should be required to submit
gauges furnished and installed by the contractor. Records detailed plans for all haul road layouts including grades,
must be made of exact locations and procedures used for widths, locations, and post-construction obliteration and
installation and initial observations. Riser pipes, tubes, or cleanup. Construction control consists generally of seeing
leads extending above the embankment surface must be that the contractor maintains and operates on the haul roads
protected from damage by earth mounds, guard posts, or in accordance with sound safety practices, and enforces
other means. Inspectors should ensure that necessary ex- adequate traffic control where public-use roads are crossed.
tensions are added as the fill is constructed to higher Haul roads should not be located near the edge of excavated
elevations. This feature of construction generally occurs at slopes where the weight of road fill and/or heavy equipment
a time when the contractor is anxious to begin or accelerate or ponding of water could endanger the stability of slopes.
embankment construction. Therefore, patience, cooperation, Haul roads up embankment slopes should be scabbed on the
and understanding must be exercised by the contractor and outside or final embankment slope and relocated periodically
the Resident Staff. where highly compacted zones could develop in the
embankment under the road which could lead to cracking.
b. Observations. Schedules for observations during The contractor should be required to remove haul roads that
construction are generally established by the design office. would endanger slope stability. The practice of placing
Pore pressure piezometers are observed frequently during pervious material across impervious zones to support heavy
construction to provide data for use in slope stability checks hauling equipment should be discouraged. If allowed, all
and to control, if necessary, the rate of fill construction on pervious material must be carefully removed. Lastly, it is
soft foundations. Initial observations should be checked to important that environmental considerations be made in
ensure their validity and accuracy, since these readings connection with haul roads so that no permanent scars in the
usually form the basis to which subsequent observations are project aesthetics remain.
related. Observations should be plotted immediately after
each set of readings is taken and evaluated for reason- b. Maintenance and public roads. Construction control
ableness against the previous set of readings. In this way, of maintenance or surface roads and public roads is required
it is often possible to detect errors in readings and to obtain to ensure compliance with specifications relating to fill,
check readings before significant changes in field conditions filter, base coarse, and pavement materials; compaction of
occur. On large projects all records should immediately be fills, subgrades, base course, and wearing course; and
processed by computers. This will generally result in the installation of drainage structures. Field compaction control
quickest results with a minimum amount of effort. Possible is similar to that required for earth fill as discussed in
sources of errors other than erroneous readings are discussed Chapter 5.
in EM 1110-2-1908. ER 1110-2-1925 prescribes the forms
6-4
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30 Sep 95
h. Progress of work, delays, causes of delays, and (1) Closed-system piezometer data.
extent of delays.
(2) Open-system piezometer data.
i. Instructions given to contractor, including name of
contractor representative talked to, and resulting actions (3) Subsurface settlement plate data.
taken by contractor.
(4) Surface reference point data.
j. Details of any controversial matters.
b. For guidance on recording of data not covered by
Appendix E, frequency of observations, and evaluating
k. Visitors to the inspector’s area of responsibility.
instrumentation data, see EM 1110-2-1908. Instructions for
submission of data to a higher echelon are contained in
l. Safety infractions/violations observed and corrective
ER 1110-2-1925.
actions taken.
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c. Observations of seepage quantities from relief wells, 7-5. Final Construction Report
toe drains, seepage galleries, and other seepage control
installations should be recorded on appropriate locally A final construction report should include the foundation
developed forms for evaluation at the project and district report outlined in ER 1110-1-1801 and the following:
levels. Unusual seepage conditions should be reported
immediately to the district office along with available a. A narrative history of the project, including schedules
observational data for evaluation of the effect of existing of starting and completing various phases, treatment of
conditions on the safety of the dam. unusual conditions, construction methods and equipment
used, quantities of materials involved, and other pertinent
7-4. Construction Foundation Report information.
b. Instructions for preparation of the foundation report, g. Results of stability and other analyses during con-
including a suggested outline, are contained in ER 1110-1- struction.
1801. Drawings in the reports should accurately pinpoint
major features and not simply be rough sketches. Photo- h. Summary of instrumentation data.
graphs are especially useful if foundation problems arise in
the future. Therefore, good photographs of major features, i. Summaries or references to conferences and in-
labeled accurately as to location, should be used liberally spection visits and resulting actions implemented.
throughout the report.
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Figure B-1. Illustration of one-point compaction Figure B-2. Illustration of possible error using one-
method and two-point compaction methods
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one-point method, consider the field density and water con- curves are not parallel. Using point A only, as in the one-
tent shown by point B in Figure B-2. Point B is close to point test method, would result in appreciable error as the
three compaction curves. Consequently, the correct curve shape of the curve would not be defined. The established
cannot be determined from the one point. The estimated compaction curve can be more accurately defined by two
maximum dry density and optimum water content could compaction points as shown. Although the two-point meth-
vary from about 92.8 pcf and 26 percent, respectively, to od is more accurate than the one-point method, neither
95.0 pcf and 24 percent, respectively, depending on which method would have acceptable accuracy when applied to the
curve was used. Therefore, the one-point method should be set of compaction curves shown in Figure B-2. There are
used only when the data define a relatively good line of materials and instances when the two-point compaction test
optimums. fails to identify the proper compaction curve. Experienced
embankment construction engineers suggest that when this
c. Two-point compaction test results. occurs, a third compaction point is necessary, and is per-
formed for proper definition of the soil compaction curve.
(1) In the two-point test, using the same equipment and
procedures used in the five-point compaction test, one d. Visual comparison. In the visual comparison meth-
sample of material from the location of the field density test od, selection of an appropriate compaction curve is based on
is compacted at the fill water content, if thought to be at or visual identification of the type of material from the field
on the dry side of optimum water content (otherwise, reduce density test with material (usually jar samples) on which
the water content by drying to this condition). A second five-point compaction tests have been run. Unfortunately,
sample of material is allowed to dry back about 2 to 3 per- materials that appear similar can have widely varying
centage points dry of the water content of the first sample compaction characteristics, and this method is not con-
and then compacted in the same manner. After compaction, sidered reliable.
the water contents of the two samples are determined by
oven drying or other more rapid means, and the dry
densities are computed. The results are used to identify the e. Atterberg limits correlations. To develop Atterberg
appropriate compaction curve for the material tested as limits correlations, liquid limit, and plastic limit determi-
shown in Figure B-3. nations and five-point compaction tests are made and plots
are prepared of optimum water content versus liquid limit,
(2) The data shown in Figure B-3 warrant the use of the versus plastic limit, and versus plasticity index. Similar
two-point compaction test since the five-point compaction plots are made of the limits values versus maximum densi-
ties. The plots are then analyzed to determine if adequate
correlations exist (exhibited by plotted points falling in a
narrow band across the plot). Figures B-4 and B-5 are
examples of such plots. If a good correlation exists, appro-
priate limits tests are performed on the field density test
material and the plots used to estimate optimum water
contents and maximum densities of the in-place material.
This method is applicable to fine-grained cohesive soils
classified as CL and CH. Statistical analyses of the data
shown in Figures B-4 and B-5 indicate relatively good
correlations. Least square linear regressions were performed
on the data shown in Figures B-4 and B-5 to determine the
“best fit” linear equations to correlate optimum water
content and maximum dry density with liquid limit and
plasticity index. Using properties of statistical parameters,
it can be shown that about 68 percent of the data points (of
true optimum water content) on Figure B-4a will lie within
plus or minus 1.4 percentage points of the indicated line of
best fit; similarly, about 65 percent of the maximum dry
density data points will lie within plus or minus 2.7 pcf of
the indicated line. (Conversely, 32 percent of the data
points will fall outside of these limits around the respective
lines). Optimum water content and maximum dry density
Figure B-3. Illustration of two-point compaction
did not correlate as well with plasticity index. Approxi-
method mately 68 percent of the actual optimum water contents and
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Figure B-4. Examples of plots of optimum water content and maximum dry density versus liquid limit
B-3
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Figure B-5. Examples of plots of optimum water content and maximum dry density versus plasticity index
B-4
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dry densities will be within ± 2.1 percent and 3.6 pcf, lines of Figures B-4 and B-5 are called the standard error of
respectively, of those indicated by the lines of best fit. the estimate. Again, if the data are normally distributed
Therefore, when this method is used, it is very important about this line, theory predicts that about 68 percent of the
that additional five-point compaction tests and Atterberg points lie between the (error band) lines. However, this also
limits tests be performed to check the correlation and to indicates that 32 percent (about one-third) of the points will
extend the correlation for new borrow material for mixtures statistically lie outside the band. For example, since the
not previously tested. The Atterberg limits correlation standard error between maximum dry density and liquid
method includes more variables than the two-point method limit is 2.7 pcf, if maximum dry density were estimated
and thus can be less accurate, depending on how carefully based on a determination of liquid limit of a soil sample
the particular method is used. However, the limits taken from the area, chances are about one in three that the
correlation method has the advantage of providing the exact error in maximum density would be greater than 2.7 pcf. In
classification of the soil, and of providing data that can be this light, the use of this procedure to estimate either
correlated with design strength studies. maximum dry density or optimum water content appears to
be unsound and inappropriate. The use of one- and two-
f. Analysis of Atterberg limits correlations. A dis- point compaction test results appears to be much more
cussion of Atterberg limits correlations and comparison of sound, especially considering that the results of a one-point
results with the one-point method are given in by Torrey compaction test may be obtained in about 40 min using
(1970). However, additional discussion of the method is microwave drying techniques outlined in paragraph 5-10d
deemed appropriate here to point out mathematical weak- (1)(c). Conversely, the time required to obtain the results of
nesses in the procedure. In order to determine a mathe- a liquid and/or plastic limit test may be prohibitive in a
matical relationship between the variables of interest (that is construction environment where large volume rates of earth
liquid limit, plastic limit, optimum water content, maximum are being placed.
dry density) using the methods of statistics, it is necessary
to assume a frequency distribution between the variables. g. USBR rapid compaction control method. Details of
It was assumed that there is a normal or Gaussian distri- this method are described in the U.S. Bureau of Reclamation
bution between the variables. A normal distribution has a Earth Manual (1963). The test is applicable to fine-grained
very specific mathematical definition and, although the (100 percent minus No. 4 sieve) cohesive soils with liquid
assumption of normal distribution is reasonable, it must be limits less than 50. The method, however, is applicable to
pointed out that there is no insurance that the assumption is soils containing oversize particles providing the proper
valid. Additionally, it was assumed that the relationship corrections, as stated in Torrey (1970) or in the Earth
between the variables of interest is linear; again, there is no Manual (1963), are applied. It is a faster method than the
evidence to support such an assumption; in fact, it is very standard compaction test, and is often more accurate than
likely that there is a curvilinear relationship between the other methods. The method usually requires adding water
variables of interest. Analysis of the data presented in Fig- to or drying back sampled fill material, and thorough mixing
ures B-4 and B-5. showed that the linear correlations be- is required to obtain uniform drying or distribution of added
tween optimum water content and liquid limit (shown in water. Otherwise, the results may be erroneous, especially
Figure B-4a) and maximum density and liquid limit (shown for highly plastic clays. In highly plastic (and probably
in Figure B-4b) explain only 77.6 percent and 76.3 percent, difficult) clays, it is likely to be inaccurate because of the
respectively, of variation between the regression line and the lack of sufficient curing time of the specimens.
data points. This means that unidentified mechanisms
explain about one quarter of the variation between the B-3. Cohesive Soils
regression line and the points. Similarly, the linear corre-
lations between optimum water content and plasticity index a. Oversize particles. The term “oversize particles” as
(shown in Figure B-5a) and maximum dry density and used in this work refers to those particles larger than the
plasticity index (shown in Figure B-5b) explain only maximum size allowed when using a given mold (i.e., No. 4
57.8 percent and 55.7 percent of the variation, respectively; for a 4-in. mold, 3/4-in. for a 6-in. mold, 2-in. for a 12-in.
about 43 percent of the observed variation is unexplained by mold). The term “fine fraction” refers to that part of the
the mathematical model chosen. In this light, the correlation soil composed of particles equal to and smaller than the
between the variables appears less sound, especially con- maximum size allowed for a given mold. Results of field
sidering that there is no mathematical assurance that a density tests made in fill material containing oversize
relationship exists between these variables; the mathematical particles must sometimes be related to results of compaction
curve-fit procedure used in the analysis ensures only that the tests made on materials from which oversize particles have
mathematical expressions given are the best possible linear been scalped, if the USBR rapid compaction control method
fits. The numbers defining the error bands of the regression is used, or if it has not been possible to perform compaction
B-5
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tests using molds of sufficient size to accommodate the should be based on laboratory compaction tests performed
large particles. in molds of appropriate sizes.
b. Correction of field density test results. When the c. Modified Ziegler equation to estimate maximum den-
proportion of oversize material is not greater than about sity. A procedure to compute dry density of earth-rock mix-
35 percent, the dry density of the fine fraction can be tures has been determined as an extension of the Ziegler
calculated with reasonable accuracy from the following procedure and is discussed by Torrey and Donaghe (1991);
equation which associates all voids with the fine fraction: the procedure is a modification of the development which
resulted in Equation B-1. The modified equation accounts
fγtγwGm for the actual percent compaction of the gravel fraction
γf (B-1) when the total material (gravel and fines) is at its maximum
γ wG m cγt
density. This is done by incorporating the effect of a factor
called the density interference coefficient, which is defined
where
as
γf = dry density of fine fraction, pcf
f = proportion of fine fraction by weight expressed Rc
Ic (B-3)
as a decimal fraction PgGm
γt = dry density of total field sample, pcf
γw = unit weight of water, 62.4 pcf where
Gm = bulk specific gravity of oversize particles (dry
method), dimensionless Rc = decimal fraction of the percent compaction of
c = proportion of oversize particles by weight the minus No. 4 or -3/4-in. fraction
expressed as a decimal fraction Pg = decimal fraction of percent gravel in the total
material
The water content of the fine fraction can be calculated Gm = bulk specific gravity of the gravel
from the following equation:
To determine the maximum dry density corresponding to the
wt cwc gradation of the total fill sample, use the equation
wf × 100 (B-2)
f
PgIcγfmaxγwGm
γtmax (B-4)
where fγw PgcIcγfmax
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B-7
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PgIcγwGm wfopt
γtmax
γw 2
(B-5) wtopt (B-7)
f Pg Ic Fopt
γfmax Pg
Figure B-7. Relationship between gravel content and Figure B-8. Relationship between gravel content and
parameters in the numerator of Equation B-5 parameters in the denominator of Equation B-5
B-8
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a. Control using relative density. Where materials source of uncertainty identified and resolved, particular care
available for cohesionless fill vary significantly in gradation, and caution should be used in determining maximum
maximum-minimum density tests should be performed on density. One method of minimizing uncertainty is to per-
material from each field density test at least in the initial form several maximum density tests to determine and ensure
construction stages. Where cohesionless materials can be that large variations in maximum density are not being
grouped into categories with relatively constant gradations, observed. A control criterion for maximum density speci-
relative density tests and gradation tests can be performed mens similar to that for minimum density specimens may be
on each different material. Gradation tests on material from used—that is, agreement between two successive specimens
field density tests can then make it possible to match field within ±1 percent.
densities with appropriate relative density test results.
However, it is necessary to point out that relative density is b. Alternative maximum density procedure. In light of
computed from maximum and minimum densities deter- the difficulty of obtaining duplicate results of maximum
mined on the material in question, using the procedure density on the vibratory table, consideration must be given
outlined in EM 1110-2-1906. It was concluded by ASTM to eliminating the test. A possible alternative procedure for
(1973) that the maximum density of cohesionless materials maximum density determination is the Modified Providence
as determined on the “vibratory table” (as described in Vibrated Density Test as described in EM 1110-2-1906. In
EM 1110-2-1906) is subject to considerable uncertainty. this test, a sample of oven-dried soil is placed in a heavy
Further, the conclusions are that vibratory tables cannot, in steel mold, compressed under a surcharge, and vibrated to
general, be successfully calibrated for repeatable energy a maximum density by repeatedly striking the side of the
application to the soil specimen, large local density mold with a hammer. Research presented by Tokue (1976)
variations exist throughout the vibrated soil specimen, and suggests that the level of shear strain, not acceleration, is
density results obtained with the vibratory table are directly related to densification of cohesionless soil. Many
generally not repeatable from laboratory to laboratory. of the unknown uncertainties associated with the vibratory
Therefore, control of the gradation and density of table may be avoided by use of this relatively simple
cohesionless fill using the method of relative density may be procedure.
unacceptable, especially if the procedure involves
coordinated effort and testing between two laboratories. An c. Materials with +3-in. particles. Relative density
example is given by ASTM (1973) in which the standard tests described in EM 1110-2-1906 are performed on cohe-
deviation in maximum density of one sand tested by sionless soils with particle sizes not greater than 3 in. If
14 laboratories is greater than 6 pcf. It is specified in cohesionless soils contain a large amount of +3-in. material,
EM 1110-2-1906 that minimum density tests be repeated large-scale field density tests would be needed for
until densities from two successive runs agree within comparison with results of field density tests performed
±1 percent. Maximum density is then obtained by placing during construction of test fills to develop adequate com-
a minimum density specimen on the vibratory table; only paction procedures. When no field density test results are
one maximum density test is required. Variation and uncer- available, control is achieved by careful inspection to ensure
tainty in laboratory-measured values of maximum density that the specified gradation is being met and that the
can cause serious problems in the construction of cohesion- specified compaction procedures are followed. Visual in-
less fill and graded filters. Basic laboratory research is spection of the sides of a test pit dug in the compacted fill
needed to resolve difficulties with the shaking table test for can provide qualitative indications of the denseness of the
maximum density. Until research is performed and the material and of the existence of any significant voids.
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(d) Weight empty and as used, type of ballast, tire (3) Method of adding water on the fill.
pressure, and load per tire as used.
(4) Method of reducing water content of the fill.
(e) Speed of travel during compaction.
d. Compaction control methods.
(3) Vibratory roller.
(1) For impervious or semipervious fill: Describe the
(a) Make and model. methods used to determine in-place density and water con-
tent. Also report method of correcting for oversize particles
(b) State size (diameter and length) and number of and for correlating field density and water content for
drums. material with oversize particles with laboratory density and
water content. Submit a copy of any reference curves used
(c) Give weight of roller empty, static weight per roller for correlating the field data with the laboratory data.
used, dynamic ground pressure exerted, type of ballast, and
vibrating frequency. (2) For pervious fill or rock fill: Describe in detail
methods used in determining laboratory maximum and mini-
(d) Speed of travel during compaction. mum densities (if different from those specified in
EM 1110-2-1906) and in determining field densities of
c. Embankment operations. pervious soils and rock fill. Also include details of methods
used for correlating field and laboratory densities in
(1) Type of equipment used in spreading and mixing the determining percent compaction or relative density and
material. details of methods used in correcting for oversize particles.
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Appendix D lines are first drawn on the plot to show the limiting values
Instructions for Preparing Periodic of water content in percentage points wet or dry of standard
optimum. A horizontal line is drawn to show the desired or
Summaries of Field Compaction Control
specified minimum percent of maximum standard and dry
Data on Earth and Rock-Fill Dams density. The top margin and right side margin of the plot
are marked to show the limiting values illustrated in
Figure D-2. The data are then plotted using symbols shown
D-1. Compaction Control Data Summary Forms on the legend. Should an area be reworked more than once
or reworked and tested more than once, only the last test
Summaries of compaction control data are prepared at least result or last set of test results should be plotted. The test
monthly, using tabular summary form, ENG Form 4287, and results are summarized in the tabulation form on the right
one or both of two summary plots: ENG Form 4287A for side of the plot in Figure D-2. Total number of tests is the
soils requiring control of both water content and density and total number of plotted data points excluding retests and
ENG Form 4287B for soils requiring only density control. check tests. Check tests should not be included in the
number retested.
D-2. Separate Summary Forms and Plots
D-5. Summary Plot for Materials Requiring Only
Separate summary forms and plots should be prepared for Density Control
(a) significantly different materials (impervious, random,
pervious, etc.) used in different zones of the embankment Use of the summary plot for material requiring only density
and (b) materials compacted by different equipment (e.g., control is illustrated in Figure D-4. Inappropriate labels at
impervious fill compacted by towed rollers and impervious the top and bottom of the plot are lined out. If control is
backfill compacted by hand-operated power tampers). based on maximum density determined using a vibratory
procedure, “STD” should also be lined out. Suitable scales
D-3. Example Summary Forms and Plots are added to the plot, and a vertical line is drawn to indicate
the minimum value of relative density, minimum percent of
Examples of prepared summary forms and plots are shown maximum standard dry density, or minimum percent of
in Figures D-1 through D-4. Examples of appropriate en- maximum dry density by a vibratory procedure, whichever
tries for tabular summaries are given in Table D-1. applies.
D-1
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Figure D-1. Example of a prepared summary form, field compaction control data, impervious (core)
D-2
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D-3
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Figure D-3. Example of a prepared summary form, field compaction control data, pervious
(sand drain)
D-4
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D-5
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Table D-1
Samples of Appropriate Entries on Tabular Summary
Method of Relating Field w to Standard Optimum w and Field Density to Maximum Dry
Compaction Equipment Density or Relative Density
Sheepsfoot roller, Bros, self-propelled, Field results compared with results of complete standard compaction test on material
SP244DA (636 psi) from field test.
Pneumatic roller, 50-ton Ferguson Model Field results compared with laboratory curves selected by two-point standard
RT-100 S, 4-wheel (80 psi) compaction test on material from field test.
Sheepsfoot roller, Southwest Model Field results compared with results of rapid compaction (USBR) tests on fill material.
2DM-120S, 25,335 lb (towed)(527 psi)
Sheepsfoot roller, Ferguson Model SP-120B, Field results compared with laboratory standard compaction results for minus 1-in.
self-propelled (615 psi) material, corrected for percent plus 1-in. material. Appropriate laboratory results
selected by Atterberg limits correlations.
Sheepsfoot roller, (towed), American Steel Compared visually with materials on which laboratory standard compaction tests were
Works, similar to Model ABD 120 (547 psi) performed.
D-8 crawler tractor (12.2 psi) Maximum (vibratory table)1 and minimum density determined for each field density test.
Pneumatic roller, 50-ton Bros Model 450, Compared with results of laboratory maximum (modified Providence vibrated) and
4-wheel (80 psi) minimum density test on minus 2-1/2-in. fraction.
Vibratory roller, Bros Model VP-20D (static Appropriate laboratory results selected by gradation correlation.
weight = 10 tons; centrifugal force = 20 tons
at 1,300 rpm)
Note: if more than one method is used, show percentage use of each method.
1
Use care to confirm reliability of maximum density as determined on the vibratory table. See the caution in Appendix B,
paragraph B-4a.
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structure in which they are installed and, as a result, the f. Electronic strain gauge piezometers. The Carlson
stress measured may be in error. Calibration of these de- piezometer and electronic pressure transducers are examples
vices can be difficult, and installation must be performed by of this design of piezometer. The principal of operation is
an experienced technician. that water pressure deflects a diaphragm which has been
strain-gauged or otherwise fitted for electronic displacement
E-4. Pore Pressure Measurement measurement. Pressure versus strain meter reading is
established by calibration so that pore water pressure is
Piezometers are instruments permanently installed in a soil determined directly by a meter reading.
or rock structure to measure fluid pressure. Several types
of piezometers based on different pressure sensing mech- g. Vibrating wire piezometers. Mechanical resonance
anisms are available for general use. Each type will be or vibrating wire transducers are sometimes used to measure
identified and the operating mechanism briefly described. water pore pressure. In these instruments, a wire under
tension is connected to (the center of) a diaphragm which
a. Open standpipe piezometer. This type of device deflects as the result of water pressure. Deflection of the
consists of an open tube in which the level of fluid is membrane changes the tension in the wire and therefore the
measured by sounding, or by lowering a tape into the tube resonant frequency of the structure. The system is con-
to measure the water level. figured so that the wire under tension may be excited to
resonance by a magnetic coil and the resonant frequency
b. Casagrande piezometer. The tip of the device measured electronically. The relationship between resonant
consists of a 2-ft-long porous tube connected to a riser pipe frequency and pressure is established by calibration. Vi-
of 3/8-in. tubing. Water level (pressure) is measured with brating wire piezometers are essentially like electronic strain
an electronic sounding device or a pressure gauge if the gauge transducers except that the internal displacement, or
water level is higher than the ground surface. strain associated with pressure change is measured using
electromechanical means.
c. Wellpoint piezometer. The instrument consists of a
perforated tip (well screen, epoxied sand filter, well strainer, E-5. Flow Measurement
etc.) connected to a standpipe. Water level is measured by
lowering a sounding device into the standpipe. Flow measurement associated with dam construction may be
achieved using two basic devices, weirs and impeller flow
d. Hydraulic piezometer. Two designs are in general transducers. Each will be briefly described.
use: the USBR device and the Bishop device. This type of
piezometer consists of two tubes leading to the tip, which a. Weirs. A weir is an obstruction in a channel that
contains a porous element common to the two tubes. The causes water to back up behind it and to flow over or
tip must be de-aired for proper operation; de-airing is ac- through it. By measuring the height of the upstream water
complished by flushing water through one tube and bleeding surface, the rate of flow is determined. Weirs constructed
through the other until saturation is achieved. One tube is from a sheet of metal or other material such that the jet, or
then shut off and the other connected to a vacuum/pressure nappe, springs free as it leaves the upstream face are called
gauge which reads fluid level directly. sharp-crested weirs. For example, the V-notch weir is a
very effective and widely used sharp-crested weir which
e. Diaphragm piezometers. Two designs are in general may be calibrated quite precisely and reliably for use in
use: the Warlan device and the Gloetzl device. The dia- flow measurement. Other weir types, such as the broad-
phragm piezometer consists of two tubes leading to the crested weir, support water flow in a longitudinal direction.
piezometric porous tip. A membrane is forced against the The relationship between flow rate versus height above the
end of one of the tubes by in situ water pressure. To make crest of a particular weir is established by calibration against
pore pressure measurement, from the observation station, air a standard with known volume discharge characteristics.
pressure is introduced into the tube that has the membrane
against it until the pore pressure acting on the opposite side b. Impeller flow transducers. The impeller flow
is slightly exceeded, allowing air past the membrane flapper. transducer consists of a flow chamber around an impeller
This air, escaping through the opposite tube, is detected with shaft and rotor. As fluid flows through the chamber, it im-
a bubble chamber at the observation station. The air pres- pinges on the blades to cause rotation of the impeller shaft,
sure is then reduced until bubbling stops, at which time the the speed of which is measured electronically with an
air pressure in the line is assumed to equal the pore water encoder. A relationship between quantity of flow and shaft
pressure. rotation speed/electronic output may be established by
E-2
EM 1110-2-1911
30 Sep 95
calibration. Impeller flow transducers are generally used to c. Mercury thermometer. A mercury thermometer is a
measure relatively small rates of flow which must be closed evacuated glass tube containing a quantity of mer-
obtained precisely. However, impeller flow transducers do cury. Mercury has a relatively high coefficient of tem-
not work well when used with water containing sediment, as perature expansion, and when the tube is placed in a
particles of grit tend to jam the mechanism, causing it to temperature environment, the mercury will expand to fill a
seize. given portion of the tube. The tube is graduated, and the
relationship between temperature and the expansion of the
E-6. Temperature Measurement mercury in the tube as quantified by graduations on the tube
is established by calibration. The mercury thermometer is
One possible benefit of temperature measurement connected very easy to use and relatively precise; however, because of
with dam construction is that it may aid in determining the the fast time response of thermal expansion of mercury, the
source of seepage or leakage water. Temperature measure- device must be used only in applications when the tube may
ment sensors may be permanently installed in a compacted be observed directly (that is, it may not be lowered into
earth structure during construction or may be mobile and boreholes).
simply lowered into boreholes for spot temperature checks.
Two electronic devices are generally used for temperature E-7. Strong Motion Monitoring
measurement, the thermocouple and the thermistor. The
mercury thermometer is also useful. Each will be briefly Strong motion monitoring is used to measure the response
described. of an embankment dam to seismic activity. The most im-
portant benefit obtained is to guide decisions on inspection
a. Thermocouples. A thermocouple is an electronic and repair after the structure has been subjected to a seismic
circuit consisting of two dissimilar metals in which a event. The information may be used to determine if the
voltage is produced when two junctions of the metals are at event was larger or smaller than the design earthquake and
different temperatures. For example, the temperature of ice to decide what repair or strengthening is needed. Instru-
water is typically used as a reference junction temperature ments for strong motion monitoring are called strong motion
and the voltage produced by the opposite junction calibrated accelographs of seismographs. The key element of the
versus temperature (of that junction). In many commercial instrument is an accelerometer, which consists of a mass
thermocouple instruments, the function of the reference suspended in a case. The case itself is securely fastened to
junction is simulated electronically. For the temperature the dam. During an earthquake, relative movement between
range expected in earth dam construction, copper/constantan the mass and the case is converted to an electrical signal
or iron/constantan thermocouples (commonly called ISA1 which is converted to either the acceleration or the velocity
J-type or T-type thermocouples, respectively) will be most of the ground motion. An accelograph also contains signal
appropriate and useful. amplifiers, a recording device such as paper, photographic
film, or magnetic tape, along with a rechargeable battery
b. Thermistors. A thermistor is a composite semi- power supply, a very accurate clock, and a motion trigger to
conductor that has a large negative temperature coefficient turn on the instrument when a predetermined level of
of resistance and, as such, can be used for temperature ground motion is exceeded. An important consideration in
measurement. The electronic circuit associated with a the design and installation of such instruments is that they
thermistor is designed to measure the resistance of the be sensitive enough to give an accurate account of the
thermistor and, therefore, the temperature-resistance charac- motion, yet be protected so that they are not damaged
teristics of the device must be established by calibration. during the event.
The electronic circuitry associated with thermistors is often
designed to produce readings directly in engineering tem-
perature units.
1
Instrument Society of America.
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EM 1110-2-1911
30 Sep 95
Construction control
Subject Page
Fill . . . . . . . . . . . . . . . . . . . . . . . . . . 5-19, 5-22
Pervious . . . . . . . . . . . . . . . . . . . . .... 5-19
Blending soil layers (See Borrow Semipervious earth . . . . . . . . . . . . . .... 5-22
area operations - Water content Importance of . . . . . . . . . . . . . . . . . . . .... 1-1
control.) Inspection . . . . . . . . . . . . . . . . . . . . . . .... 1-1
Borrow area and quarries . . . . . . . . . . . . . . . . . . . 4-1 Personnel . . . . . . . . . . . . . . . . . . . . . . . .... 2-2
Earth fill (See Equipment, Procedures . . . . . . . . . . . . . . . . . . . . . . .... 5-7
earth-fill and rock-fill and Purpose of . . . . . . . . . . . . . . . . . . . . . . .... 1-1
Borrow area operations.) Relation to design . . . . . . . . . . . . . . . . . .... 1-1
Final conditions . . . . . . . . . . . . . . . . . . . . . . 4-11 Test fill . . . . . . . . . . . . . . . . . . . . . . . . .... 5-1
Borrow areas . . . . . . . . . . . . . . . . . . . . . 4-11 Test quarries . . . . . . . . . . . . . . . . . . . . .... 4-10
Quarries . . . . . . . . . . . . . . . . . . . . . . . . 4-11 Verification of requirements . . . . . . . . . . .... 2-4
Spoil areas . . . . . . . . . . . . . . . . . . . . . . . 4-11 Construction, earth-fill and rock-fill . . . . . . . . .... 5-1
Obtaining rock fill (See Earth test fills (See Test fills,
Rock-fill, obtaining.) earth.)
Rock excavation (See Equip- Equipment (See Equipment,
ment, rock excavation.) earth-fill and rock fill.)
Test quarries (See Quarries, Impervious fills (See Fill,
test.) impervious and semipervious.)
Borrow area operations . . . . . . . . . . . . . . . . . . . . . 4-5 Pervious fills (see Fill,
Blending soil layers . . . . . . . . . . . . . . . . . . . 4-7 pervious.)
Equipment . . . . . . . . . . . . . . . . . . . . . . . 4-7 Placement sequence . . . . . . . . . . . . . . . . . . . 5-22
Methods . . . . . . . . . . . . . . . . . . . . . . . . 4-7 Quantity measurement . . . . . . . . . . . . . . . . . . 5-23
Reasons for . . . . . . . . . . . . . . . . . . . . . . 4-7 Rock fill (See Fill, rock.)
Cold weather . . . . . . . . . . . . . . . . . . . . . . . . 4-8 Rock test fills (See Test fills, rock.)
Deviations . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5 Semipervious fills (See Fill,
Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5 impervious and semipervious.)
Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7 Slope protection . . . . . . . . . . . . . . . . . ..... 5-23
Plans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5 Placement of protection . . . . . . . . . 5-23, 5-25
Stockpiling . . . . . . . . . . . . . . . . . . . . . . . . . 4-7 Reasons for . . . . . . . . . . . . . . . . . ..... 5-23
Water content control . . . . . . . . . . . . . . . . . . 4-6 Types of damage . . . . . . . . . . . . . ..... 5-23
Dry soil . . . . . . . . . . . . . . . . . . . . . . . . . 4-6 Types of protection . . . . . . . . . . . . 5-23, 5-25
Wet soil . . . . . . . . . . . . . . . . . . . . . . . . 4-6 Construction features, miscellaneous . . . . . . ..... 6-1
Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1 Drainage, surface . . . . . . . . . . . . . . . . ..... 6-3
Clay shales . . . . . . . . . . . . . . . . . . . . . . . . . 3-6 Necessity . . . . . . . . . . . . . . . . . . . ..... 6-3
Foundations and abutments, Methods . . . . . . . . . . . . . . . . . . . ..... 6-3
rock . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2 Instrumentation . . . . . . . . . . . . . . . . . ..... 6-3
Slurry trench . . . . . . . . . . . . . . . . . . . . . . . . 3-4 River diversion . . . . . . . . . . . . . . . . . . ..... 6-1
Compaction, impervious and semi- Closure section . . . . . . . . . . . . . . . ..... 6-1
pervious fill . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6 Cofferdams, embankment-type . . . . ..... 6-1
Adverse weather . . . . . . . . . . . . . . . . . . . . . . 5-15 Roads . . . . . . . . . . . . . . . . . . . . . . . . ..... 6-4
Confined areas . . . . . . . . . . . . . . . . . . . . . . . 5-16 Haul . . . . . . . . . . . . . . . . . . . . . . ..... 6-4
Density . . . . . . . . . . . . . . . . . . . . . . . . . 5-6, 5-7 Maintenance . . . . . . . . . . . . . . . . . ..... 6-4
Field compaction effort . . . . . . . . . . . . . . . . . 5-6 Public . . . . . . . . . . . . . . . . . . . . . ..... 6-4
Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . 5-6 Service bridge pier foundations . . . . . . ..... 6-3
Lift thickness . . . . . . . . . . . . . . . . . . . . . 5-7, 5-8 Stage construction . . . . . . . . . . . . . . . ..... 6-3
Inspection . . . . . . . . . . . . . . . . . . . . . . . 5-8 Features . . . . . . . . . . . . . . . . . . . . ..... 6-3
Specifications . . . . . . . . . . . . . . . . . . . . . 5-7 Necessity . . . . . . . . . . . . . . . . . . . ..... 6-3
Placement water content . . . . . . . . . . . . . 5-6, 5-7 Construction records (See Records and
Specifications . . . . . . . . . . . . . . . . . . . . . . . . 5-6 reports, construction.)
Standard compaction effort . . . . . . . . . . . . . . 5-6 Contractor
Water content . . . . . . . . . . . . . . . . . . . . 5-7, 5-8 Relations with resident engineer . . . . . . . . . . . 2-3
Index-1
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Index-2
EM 1110-2-1911
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Index-3
EM 1110-2-1911
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Index-4
EM 1110-2-1911
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Index-5