Designation: C 12 – 07

Standard Practice for

Installing Vitrified Clay Pipe Lines1
This standard is issued under the fixed designation C 12; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript
epsilon (e) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.

1. Scope DESIGN CONSIDERATIONS

1.1 This practice covers the proper methods of installing 4. Supporting Strength
vitrified clay pipe lines in order to fully utilize the structural
properties of such pipe. 4.1 The field supporting strength of vitrified clay pipe is
1.2 The values stated in inch-pound units are to be regarded materially affected by the methods of installation. The field
as the standard. The values given in parentheses are for supporting strength of a pipe is defined as its capacity to
information only. support dead and live loads under actual field conditions. It is
1.3 This standard does not purport to address all of the dependent upon two factors: (1) the inherent strength of the
safety concerns, if any, associated with its use. It is the pipe and (2) the bedding of the pipe.
responsibility of the user of this standard to establish appro- 4.2 The minimum bearing strength requirement in accor-
priate safety and health practices and determine the applica- dance with Specification C 700, as determined by the 3-edge-
bility of regulatory limitations prior to use. bearing test of Test Methods C 301, is a measure of the
inherent strength of the pipe.
2. Referenced Documents 4.3 The tests used to measure bearing strength determine
2.1 ASTM Standards: 2 relative pipe strengths but do not represent actual field condi-
C 301 Test Methods for Vitrified Clay Pipe tions. Therefore, an adjustment called a load factor is intro-
C 425 Specification for Compression Joints for Vitrified duced to convert minimum bearing strength to field supporting
Clay Pipe and Fittings strength. The magnitude of the load factor depends on how the
C 700 Specification for Vitrified Clay Pipe, Extra Strength, pipe is bedded. The relationship is:
Standard Strength, and Perforated Field supporting strength 5 minimum bearing strength 3 load factor
C 828 Test Method for Low-Pressure Air Test of Vitrified 4.4 A factor of safety greater than 1.0 and less than or equal
Clay Pipe Lines to 1.5 shall be applied to the field supporting strength to
C 896 Terminology Relating to Clay Products calculate a safe supporting strength. The relationship is:
C 1091 Test Method for Hydrostatic Infiltration Testing of
Field supporting strength
Vitrified Clay Pipe Lines Safe supporting strength 5 Factor of safety
D 2487 Practice for Classification of Soils for Engineering
Purposes (Unified Soil Classification System) 5. External Loads
3. Terminology 5.1 The external loads on installed vitrified clay pipe are of
two general types: (1) dead loads and (2) live loads.
3.1 General—Terminology C 896 can be used for clarifica-
5.2 For pipes installed in trenches at a given depth, the dead
tion of terminology in this specification.
load increases as the trench width, measured at the top of the
pipe, increases. Consequently, the trench width at the top of the
pipe shall be kept as narrow as possible. Pipe failure may result
1
This practice is under the jurisdiction of ASTM Committee C04 on Vitrified if the design trench width is exceeded. If the trench width
Clay Pipe and is the direct responsibility of Subcommittee C04.20 on Methods of
Test and Specifications. exceeds the design width, a higher class of bedding, stronger
Current edition approved April 1, 2007. Published April 2007. Originally pipe, or both, must be investigated.
approved in 1915. Last previous edition approved in 2006 as C 12 – 06.
2
5.3 Live loads that act at the ground surface are partially
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
transmitted to the pipe. Live loads may be produced by wheel
Standards volume information, refer to the standard’s Document Summary page on loading, construction equipment or by compactive effort.
the ASTM website. Compaction of embedment and backfill materials, beside and

Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.

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 C 12 – 07
Construction, Water Pollution Control Federation Manual of Practice No.
FD-5, American Society of Civil Engineers—Manuals and Report on
Engineering Practice—No. 60.3

6. Bedding and Encasement

6.1 Classes of bedding and encasements for pipe in trenches
are defined herein. The load factors indicated are for conver-
sion of minimum bearing strength to field supporting strength.
6.2 Class D (Fig. 2)—The pipe shall be placed on a firm and
unyielding trench bottom with bell holes provided (Fig. 9). The
initial backfill shall be of selected material (Note 2).
6.2.1 The load factor for Class D bedding is 1.1.
NOTE 2—Selected material is finely divided material free of debris,
organic material, and large stones.
6.3 Class C (Fig. 3)—The pipe shall be bedded in clean
coarse-grained gravels and sands as defined in Practice D 2487,
Table 1, (types SW, SP, GW, GP) (Note 4). Angular, non-
consolidating bedding material not subject to migration may be
specified (as in Note 3). The bedding shall have a minimum
thickness beneath the pipe of 4 in. (100 mm) or one eighth of
the outside diameter of the pipe, whichever is greater, and shall
extend up the haunches of the pipe one sixth of the outside
diameter of the pipe. The initial backfill shall be of selected
material (Note 2).
6.3.1 The load factor for Class C bedding is 1.5.
NOTE 3—Suitable material is well-graded 3⁄4 to 1⁄4 in. (19 to 6.4 mm)
crushed stone, having a minimum of one fractured face, or other angular,
non-consolidating bedding material not subject to migration. Well-graded
angular, non-consolidating bedding materials are more stable than
rounded bedding materials of equal gradation. Material shall be shovel-
FIG. 1 Terminology sliced so the material fills and supports the haunch area and encases the
pipe to the limits shown in the trench diagrams (Figs. 3-6 and Fig. 8).
NOTE 4—Sand is suitable as a bedding material in a total sand
environment but may be unsuitable where high and rapidly changing
water tables are present in the pipe zone. It may also be undesirable for
bedding, or haunching in a trench cut by blasting or in trenches through
clay type soil. Regardless of the trench condition or bedding class, the
maximum load factor for sand bedding is 1.5.
6.4 Class B (Fig. 4)—The pipe shall be bedded in suitable
material (Note 3). The bedding shall have a minimum thick-
ness beneath the pipe of 4 in. (100 mm) or one eighth of the
outside diameter of the pipe, whichever is greater, and shall
extend up the haunches of the pipe to the springline. The initial
backfill shall be of selected material (Note 2).
FIG. 2 Class D
6.4.1 The load factor for Class B bedding is 1.9.
6.5 Crushed Stone Encasement (Fig. 5)—There are specific
sites where crushed stone encasement may be desirable. The
above the sewer pipe, produces a temporary live load on the crushed stone shall extend to the specified trench width and
pipe. The magnitude of the live load from compactive effort shall have a minimum thickness beneath the pipe of 4 in. (100
varies with soil type, degree of saturation, degree of compac- mm) or one eighth of the outside diameter of the pipe,
tion and depth of cover over the pipe. Care must be used in whichever is greater, and shall extend upward to a horizontal
selection of compaction methods so that the combined dead plane at the top of the pipe barrel (see Note 5). Encasement
load and live load does not exceed the field supporting strength shall consist of well-graded 3⁄4 to 1⁄4 in. (19 to 6.4 mm) crushed
of the pipe, or cause a change in its line or grade.
NOTE 1—For generally accepted criteria and methods for determining 3
Available from American Society of Civil Engineers, 1801 Alexander Bell Dr.,
loads and supporting strengths, see Gravity Sanitary Sewer Design and Reston, VA 20191.

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 C 12 – 07

FIG. 3 Class C

FIG. 4 Class B

FIG. 5 Crushed Stone Encasement

stone or other non-consolidating bedding material not subject the inherent strength of the pipe, completely filling the haunch
to migration. Material shall be carefully placed into the pipe area, and reducing the trench load on the pipe.
haunches (Note 3). The initial backfill shall be of selected 6.6.1 The pipe shall be bedded on crushed stone or other
material (Note 2). suitable material (Note 3 and Note 4). The bedding shall have
NOTE 5—Sufficient crushed stone or other suitable material (Note 3) a minimum thickness beneath the pipe of 4 in. (100 mm) or one
shall be placed so that the bedding extends to a horizontal plane at the top eighth of the outside diameter of the pipe, whichever is greater.
of the pipe barrel following removal of any trench sheeting or boxes. Controlled low strength material shall be directed to the top of
6.5.1 The load factor for crushed stone encasement is 2.2. the pipe to flow down on both sides to prevent misalignment.
6.6 Controlled Low Strength Material (Fig. 6)—Controlled Fill to the top of the pipe. The initial backfill may be placed
low strength material has been shown to be an economic when the pour is capable of supporting the backfill material
alternative to compacted bedding material. It assists in utilizing without intermixing.

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 C 12 – 07

NOTE 1—This type of construction requires the fill to extend from the pipe to the trench wall, not to extend above the top of the pipe or below the
bottom of the pipe. Where native soils are expansive, further investigation may be necessary.
FIG. 6 Controlled Low Strength Material (CLSM)

NOTE 1—Minimum width of concrete cradle: Bc + 8 in. (205 mm) or 1-1⁄4 Bc.
NOTE 2—p is the ratio of the area of steel to the area of concrete. (It is recommended that wire mesh reinforcement or uniformly distributed small
diameter rebar be used in all concrete design.)
FIG. 7 Concrete Cradle

6.7 Class A—This class of bedding can be achieved with

either of two construction methods.
NOTE 6—Attention is directed to terminology and material references.
See American Concrete Institute Report: ACI 229R-94 Controlled Low 6.7.1 Concrete Cradle (Fig. 7)—The pipe shall be bedded in
Strength Materials (CLSM).4 a monolithic cradle of reinforced concrete having a thickness
under the barrel of at least 6 in. (150 mm) or one fourth of the
6.6.2 The load factor for controlled low strength material is
outside diameter of the pipe, whichever is greater, and extend-
2.8.
ing up the haunches to a height of at least one half the outside
diameter of the pipe. The cradle width shall be at least equal to
4
Available from American Concrete Institute, P.O. Box 9094, Farmington Hills, the outside diameter of the pipe plus 4 in. (100 mm) on each
MI 48333. side or one and one fourth times the outside diameter of the

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 C 12 – 07

NOTE 1—Minimum width of concrete arch: Bc + 8 in. (205 mm) or 11⁄4 Bc.
NOTE 2—p is the ratio of the area of steel to the area of concrete. (It is recommended that wire mesh reinforcement or uniformly distributed small
diameter rebar be used in all concrete design.)
FIG. 8 Concrete Arch

pipe barrel, of 6 in. (150 mm) or one fourth of the nominal

diameter of the pipe, whichever is greater. The width of the
arch shall be at least equal to the outside diameter of the pipe
plus 4 in. (100 mm) on each side, or one and one fourth times
the outside diameter, whichever is greater. If the trench width
is greater than either of these dimensions, concrete may be
placed to full trench width.
6.7.2.1 The load factor for Class A concrete arch bedding is
3.4 for reinforced concrete with p = 0.4 %, and up to 4.8 for
reinforced concrete with p = 1.0 %, where p is the percentage
of the area of transverse steel to the area of concrete above the
FIG. 9 Uniform Pipe Support top of the pipe barrel as shown in Fig. 8.
6.8 Concrete Encasement:
6.8.1 There are specific sites where concrete encasement
pipe, whichever is greater. If the trench width is greater than
may be desirable. Concrete encasement shall completely sur-
either of these dimensions, concrete may be placed to full
round the pipe and shall have a minimum thickness, at any
trench width. Suitable material shall extend upward to a
point, of one fourth of the outside diameter of the pipe or 4 in.
horizontal plane at the top of the pipe barrel. The initial backfill
(100 mm), whichever is greater.
shall be selected material.
6.8.2 The encasement shall be designed by the engineer to
6.7.1.1 The load factor for Class A concrete cradle bedding
suit the specific use.
is 3.4 for reinforced concrete with p = 0.4 %, where p is the
percentage of the area of transverse steel to the area of concrete
at the bottom of the pipe barrel as shown in Fig. 7. CONSTRUCTION TECHNIQUES
6.7.2 Concrete Arch (Fig. 8)—The pipe shall be bedded in
suitable material (Note 3). The bedding shall have a minimum 7. Trench Excavation
thickness beneath the pipe of 4 in. (100 mm) or one eighth of 7.1 Trenches shall be excavated to a width that will provide
the outside diameter of the pipe, whichever is greater, and shall adequate working space, but not more than the maximum
extend up the haunches of the pipe to the springline. The top design width. Trench walls shall not be undercut.
half of the pipe shall be covered with monolithic reinforced 7.2 The trench walls can be sloped to reduce trench wall
concrete arch with a minimum thickness from the top of the failure. This sloping will not increase the load on the pipe

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 C 12 – 07
TABLE 1 Joint Deflection Limits
NOTE 1—For calculating the minimum radius of curvature use the following:
pipe—3 in. (76 mm) to 12 in. (305 mm) Diameter radius = 24 3 pipe length
pipe—15 in. (380 mm) to 24 in. (610 mm) Diameter radius = 32 3 pipe length
pipe—27 in. (685 mm) to 36 in. (915 mm) Diameter radius = 48 3 pipe length
pipe—39 in. (990 mm) to 48 in. (1220 mm) Diameter radius = 64 3 pipe length
NOTE 2—Material is applicable to compression joints for vitrified clay pipe and fittings in accordance with Specification C 425.
Maximum Angular Maximum Deflection
Nominal Diameter,
Deflection per Joint, of Pipe,
in. (mm)
degrees in./linear ft (mm/linear m)
3–12 (76–305) 2.4° ⁄ (42)
12

15–24 (380–610) 1.8° ⁄ (31)

38

27–36 (685–915) 1.2° ⁄ (21)

14

39–48 (990–1220) 0.9° 3⁄16 (16)

provided the measured trench width at top of pipe does not 11. Pipe Laying
exceed the design trench width. 11.1 Clean joint contact surfaces immediately prior to
7.3 Trenches, other than for Class D bedding, shall be joining. Use joint lubricants and joining methods, as recom-
excavated to provide space for the pipe bedding. mended by the pipe manufacturer.
7.4 Sheet, shore, and brace trenches, as necessary, to pre- 11.2 Unless otherwise required, lay all pipe straight between
vent caving or sliding of trench walls, to provide protection for changes in alignment and at uniform grade between changes in
workmen and the pipe, and to protect adjacent structures and grade. Excavate bell holes for each pipe joint. When joined in
facilities. the trench, the pipe shall form a true and smooth line.
7.5 Sheeting shall not be removed below the top of the pipe 11.3 Straight lengths of pipe may be used for horizontal or
if the resulting slope of native soil increases the trench width to vertical curves by uniformly deflecting each joint. The joint
such an extent that the load on the pipe exceeds the safe field deflection limits shall be as described in Table 1.
supporting strength of the pipe and bedding system. 11.4 Whenever practicable, start pipe laying at the lowest
7.6 When a movable box is used in place of sheeting or point and install the pipe so that the spigot ends point in the
shoring, secure the installed pipe to prevent it from moving direction of flow to prevent bedding material from entering the
when the box is moved. joint.
7.7 It is preferable to keep the trench dry during all phases 11.5 After each pipe had been brought to grade, aligned, and
of construction. Exercise caution when terminating the dewa- placed in final position, deposit and shovel slice or spade
tering procedure to avoid disturbing the pipe installation. bedding material under the pipe haunches. Wyes and tees shall
be bedded to prevent shear loading.
8. Trench Foundation
11.6 Place pipe that is to be bedded in concrete cradle or
8.1 The trench foundation is the area below the pipe and encased in concrete, in proper position on temporary supports.
bedding which supports the pipe bedding structure. When necessary, rigidly anchor or weight the pipe to prevent
8.2 The trench foundation shall be firm and unyielding. flotation as concrete is placed.
11.7 Place concrete for cradles, arches, or encasement
9. Pipe Bedding
uniformly on each side of the pipe and deposit at approxi-
9.1 Bell holes shall be excavated to prevent point loading of mately its final position. Concrete placed beneath the pipe shall
the bells or couplings of laid pipe, and to establish full-length be sufficiently workable so that the entire space beneath the
support of the pipe barrel (Fig. 9). pipe can be filled without excessive vibration.
9.2 Bedding shall be placed so that the pipe is true to line 11.8 Where pipe connects with outside faces of manhole
and grade and to provide uniform and continuous support of walls or the outside faces of the walls of other structures,
the pipe barrel. provide a pipe joint such that slight flexibility or motion can
take place in or near the plane of the wall face. It is
10. Pipe Handling recommended that a 12 to 18 in. (305 to 455 mm) pipe stub be
10.1 Pipe and fittings shall be handled carefully to protect extended from manhole or other wall faces. The pipe stub shall
from damage. be bedded in the same manner as the pipe.
10.2 Carefully examine each pipe and fitting before instal-
lation, for soundness and specification compliance. Pipe ac- 12. Backfilling Trenches
cepted may be plainly marked by the inspector. Rejected pipe 12.1 Initial backfill need not be compacted to develop field
shall not be defaced, but shall be replaced with pipe that meets supporting strength of the pipe. Final backfill may require
specification. compaction to prevent settlement of the ground surface.
10.3 Handle pipe so that premolded jointing surfaces or 12.2 Unless otherwise directed, backfill trenches as soon as
attached couplings do not support the weight of the pipe. Do practicable after the pipe is laid. In the case of concrete
not damage the jointing surfaces or couplings by dragging, bedding, delay backfilling until the concrete has set sufficiently
contact with hard materials, or by use of hooks. to support the backfill load.

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 C 12 – 07
12.3 The initial backfill shall be of selected material (Note 13.3 Where ground water does not exist above the top of the
2). Final backfill shall have no rock or stones having a pipe, Test Method C 828 is recommended.
dimension larger than 6 in. (150 mm) within 3 ft. (0.92 m) of
the top of the pipe. NOTE 8—When water or air tests are specified and the acceptance of a
line depends upon satisfactory results, it should be recognized that several
12.4 Puddling, jetting, or water flooding may be used for
factors have a bearing on these results. Manhole bases, walls, and seals
consolidating backfill material only when approved by the
must be watertight. Household and commercial building and roof drains
engineer. must be isolated. Stoppers must be sufficiently secured to be air or
watertight.
13. Field Performance and Acceptance
13.1 After installation the sewer shall be tested for integrity 13.4 In order for the performance of the line to be accept-
by a method specified or approved by the engineer. able, all tests shall be made on pipe laid in accordance with the
bedding provisions of Section 6. Joining procedures shall
NOTE 7—It is recommended that the contractor perform testing as the
installation progresses. follow the recommendation of the pipe manufacturer.
13.2 Where ground water exists above the top of the pipe,
14. Keywords
the line may be tested for infiltration by determining the
quantity of water entering the system during a specified time 14.1 backfilling; bedding; clay pipe; compaction; construc-
period. Infiltration testing is recommended and shall conform tion; design; excavation; installation; load factors; perforated
to the test procedure described in Test Method C 1091. pipe; pipe; sewers; trench foundation; trenching; vitrified

APPENDIX

(Nonmandatory Information)

X1. INSTALLATION CRITERIA FOR PERFORATED VITRIFIED CLAY PIPE

X1.1 Position of Perforations: X1.3 Bedding and Backfill:

X1.1.1 Perforations in a subdrain or leachate pipe shall X1.3.1 Bedding and backfill shall be in accordance with the
normally be down. engineer’s design.
X1.1.2 Under unique conditions it may be desirable to place
X1.3.2 It is desirable to contain the bedding with a filter
the perforations up.
fabric.
X1.2 Method of Design: X1.3.3 In the pipe zone the material shall be free draining
X1.2.1 Design in accordance with standard engineering without migration.
practice, noting particularly, the bearing strength as listed in X1.3.4 Extreme care should be exercised in placement and
Specification C 700. compaction of backfill.

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