GEOTECHNOLOGY-I(CEPC-33)

Unit 1 Sub-Surface Exploration

Dr. Jitendra Singh Yadav

Assistant Professor-I
Dept of Civil Engineering
NIT Kurukshetra, Kurukshetra Haryana

8/3/2023 1
 CONTENT
• Purpose
• Stages in soil exploration
• Depth and lateral extent of exploration
• Guidelines for various types of structures
• Ground water observations
• Excavation and boring methods
• Soil sampling and disturbance
• Major types of samplers
• Sounding methods-SCPT, DCPT, SPT and interpretation
• Geophysical methods
• Pressure-meter test
• Exploration logs

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METHODS OF EXPLORATION: Direct methods

Drifts and shafts

Open
Excavation
Pits and Trenches

Auger boring
Soil Exploration
Wash boring

Borings Rotary drilling

Percussion drilling

Core drilling

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Open excavation( for depth <6m) –IS 4453-1967 Short Summary
▪ Trial pits -1.2m* 1.2m( IS 4453-1967)
▪ Depth > 3m- lateral support
▪ Proper ventilation and dewatering if necessary

▪ Trenches-long shallow continuous pit, exposing a line

▪ Drifts(adits)-horizontal tunnels along hillside, especially for rocks

▪ Min 1.5m(b) * 2m (h)
▪ Lateral support if unstable
▪ Generally expensive
▪ Helps to establish minimum excavation limits to reach sound rocks, & to locate failure and shear zones

▪ Shafts: Large vertical holes(min 2.4m width or diameter)

▪ For D>4m
▪ Proper support and ventilation required

▪ The in-situ conditions are examined visually. It is easy to obtain disturbed and undisturbed samples (Block samples can be
cut by hand tools and tube samples can be taken from the bottom of the pit.)
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Trial Pits
•Open type
•Trial pits are shallow excavations going down to a depth not greater 6m.
•For greater depths (over 6 m) and below ground-water table, the method becomes expensive due to the expense of sheet
piling or caissons which are required in such cases.
•The trial pit as such is used extensively at the surface for block sampling and detection of services prior to borehole excavation.
•Can be dug by hand or mechanical excavator
•Only suitable in dry area as they allow hand cut samples to be taken which minimize the disturbance of sample
•Most suitable use in exploring back filled area and sites overlain by variable natural deposits
•For safety ALL pits below a depth of 1.2m must be supported.
• Cost increases with depth.
•Soil samples obtained are useful for soil classification and determination of strength properties.

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Trial Pits

Pick and
shovel Backhole
Depth Excavation Method
0-2m By Hand
2-4m Wheeled Back Hoe Trial Pit
4-6m Hydraulic Excavator 6m > depth

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Borings /drilling
• Process of making a hole for exploration of subsurface medium.
To understand soil/rock types with depth.
To observe ground water table
Possible fluctuation in stratification by means of multiple boreholes.
To collect soil samples from the depth of interest.

• A borehole is used to determine the nature of the ground (usually below 6m depth) in a qualitative manner.

• These provide both disturbed as well as undisturbed samples depending upon the method of boring.

• Where this is not possible, for in gravelly soils below the water table, in-situ testing methods are used.

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Borings /drilling
Obviously the information gained from a borehole is an extremely limited picture of the subsurface structure.
It is therefore essential to compare the results obtained with those that could have been expected from the desk study.
The greater the number of boreholes the more certain it is possible to be of the correlation and thus to trust in the results.
The two principal types of boring machine used for Site Investigation which is light percussive and drilling machines.

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Boring Methods of Exploration
➢In selecting the boring method for a particular job, consideration should be made for the following:
•The materials to be encountered and the relative efficiency of the various boring methods in such materials.
•The available facility and accuracy with which changes in the soil and ground water conditions can be
determined.
•Possible disturbance of the material to be sampled.
• Site access.
The different types of boring methods are :
1. Auger boring.: preferred for shallow depths , low ground water table
2. Wash boring: high water table, deeper soil deposit
3.Rotary drilling: high quality boring, also for rock drilling
4. Percussion drilling: fast drilling, not taking samples
5. Displacement boring
6. Continuous sampling

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1. Auger boring
•Auger is a device which in addition to excavating a soil mass also advances the borehole to deeper depths.
•Made from brass, aluminum etc. depending upon the medium to be used in.
•Can be hand operated or power driven (depending upon the depth of interest)
•This method is fast and economical, using simple, light, flexible and inexpensive instruments for large to small
holes.
•Advanced by pressing followed by simultaneous rotation.
•Choice of auger depends upon soil type available.
•In case sides of boreholes can’t sustain on their own a shell or casing is provided.
• Firstly, the casing will be driven followed by augering.
• Once reached depth of interest, augers are withdrawn thus bringing soils from the depth.

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•It is very suitable for soft to stiff cohesive soils and also can be used to determine ground water table.
•Soil removed by this is disturbed but it is better than wash boring, percussion or rotary drilling.
•It is not suitable for very hard or cemented soils, very soft soils, as then the flow into the hole can occur and also for fully
saturated cohesionless soil.
•Simplest and most common method of boring for small projects in soft cohesive soils. – Fast, economical, light, inexpensive
and flexible.

▪ Auger- a drill for advancing holes

▪ Has a shank with cross wise handle to apply torque
▪ The length of the auger blade varies from 0.3-0.5m.
▪ Diameter of central rod almost 18mm
▪ Auger held vertically and driven by applying torque, either manually or mechanically
▪ Driving force: Torque on handle + downward pressing force
▪ The auger is rotated until it is full of soil, then it is withdrawn to remove the soil and the soil type present at various
depths is noted.
▪ Hand augers and mechanically operated auger
▪ Post hole augers: for taking samples when hole is already dug/driven
Type of augers
1. Screw augers: used in very cohesive, soft or hard soils. Cannot used for dry sandy
soil.
2. Dutch augers: Suitable for wet, highly fibrous, heavy rooted swampy areas. Not
suitable for dry and sandy soils.
3. Bucket augers: Can be used for any type of soils. Samples collected are semi -
disturbed .
4. Planer auger: almost undisturbed sample.
5. Stone soil auger: stony soils or gravelly soils containing small stones or asphalts.
6. Stone catcher: Used to remove larger rocks from auger holes so that boring can be
continued with another auger. Used to very hard, rigid soils such as lime stone
deposits chalks etc.
Hand augers
▪ Hand-augered holes can be made upto about 20m depth→ although
depth greater than about 8-10m is usually not practical.
▪ The range of diameter of holes is from 50mm (2inch) to about
300mm(12 inch) drilled by different augers.

▪ Usually used for shallow depth applications→ rail road, highways etc

▪ Repeated withdrawal of auger for soil removal makes boring difficult

below 8-10m depth.

▪ Highly disturbed samples (but better than other boring methods)→

used for classification purpose and basic tests only

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Mechanical Augers: > 12m depth
▪ Power operated →The power required to rotate the auger depends on the type and size of auger and
the type of soil.

▪ Downwards pressure → applied hydraulically, mechanically or by dead weight

▪ The diameter of the flight auger → between 75 to 300mm.

▪ Borehole depths up to 50m are possible with continuous-flight augers.

▪ The most common method → continuous flight augers→ can be solid stem or hollow stem with
internal diameter of 75-150mm.
▪ Hollow stem augers → used for undisturbed samples → Plug is withdrawn and sampler is
lowered down and driven in to the soil below the auger.
▪ Auger acts as a casing it can be used in sand below water table. The possibility of rising sand in to
the stem by hydrostatic pressure can be avoided by filling the stem with water up to the water table
▪ The soil rises to the surface along the helical blades, obviating the necessity of withdrawal.

https://www.youtube.com/watch?v=T6neYRCgdTw
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Disadvantages of auger boring
▪ Difficult in:

▪ hard soil and soil containing gravels- cobbles and boulders create problems with small-sized augers

▪ very soft clay or coarse sand-hole tends to collapse when auger is removed
▪ Possibility that different soil types may become mixed as they rise to the surface and it may be difficult to determine
the depths of changes of strata.
▪ Experienced driller can however detect the change of strata by the change of speed and the sound of drilling.

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2. Wash boring:
•Commonly used for subsurface exploration below ground water table level.
•Suitable except soils mixed with gravels and boulders.
•It is a popular method due to the use of limited equipments.
•The advantage of this is the use of inexpensive and easily portable handling and drilling equipments.
•Here first an open hole is formed on the ground so that the soil sampling or rock drilling operation can be done below the hole.
•Driving force: jetting action of water + chopping action of chisel
•The hole is advanced by chopping and twisting action of the light bit.
•Cutting is done by forced water and water jet under pressure through the rods operated inside the hole.
•In India the “Dheki” operation is used, i.e., a pipe of 5cm diameter is held vertically and filled with water using horizontal lever
arrangement and by the process of suction and application of pressure, soil slurry comes out of the tube and pipe goes down.

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•It gives completely disturbed sample and is not suitable for very soft soil, fine to medium
grained cohesionless soil and in cemented soil.
•This can be done upto a depth of 8m –10m (excluding the depth of hole already formed
beforehand) Just by noting the change of colour of soil coming out with the change of soil
character can be identified by any experienced person.
Limitation
 Very disturbed sample

 Cannot be used for evaluation of engineering properties

 Sample can be extracted by replacing the drilling bit with a sampler

https://www.youtube.com/watch?v=8PpbBnstrgs
Wash boring: mud rotary drilling (soil) or core drilling (rock).
•Mud Rotary
• Hollow drill rods with a drill bit is rotated into the soil.
• Drilling mud is continuously pumped into the hole.
• The bit grinds the soil and the return flow brings the cuttings to the surface.
•Core Drilling
• Used for obtaining rock cores.
• A core barrel is fitted with a drill bit is attached to hollow drill rods.
• Examples: diamond coring, calyx or shot core drilling
Coring Bits:
• The three basic categories of coring bits in use are diamond, carbide insert, and saw tooth.
• Diamond coring bits may be of the surface set or diamond impregnated type. The most versatile of all
coring bits are the diamond coring bits.
• This is because they produce high quality cores in rock materials ranging from soft to extremely hard.
• Carbide insert bits use tungsten carbide in lieu of diamonds. Bits of such type are used to core soft to
medium hard rock.
• Even though they are less expensive than diamond bits, the rate of drilling is slower than with diamond
bits.
• The cutting edge comprises a series of teeth in saw tooth bits.
• The teeth are faced and tipped with a hard metal alloy such as tungsten carbide in order to provide wear
resistance and thereby increase the life of the bit.
• These bits are less expensive but normally used to core overburden soil and very soft rocks only.

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3. Rotary drilling
•Rotary drilling method of boring is useful in case of highly resistant strata.
•It is related to finding out the rock strata and also to access the quality of rocks from cracks, fissures and joints.
• It can conveniently be used in sands and silts also.
•Here, the bore holes are advanced in depth by rotary percussion method which is similar to wash boring technique.
•A heavy string of the drill rod is used for choking action.
•The broken rock or soil fragments are removed by circulating water or drilling mud pumped through the drill rods and
bit up through the bore hole from which it is collected in a settling tank for recirculation.

▪ Functions of drilling fluid:

▪ cools and lubricates the drilling tool
▪ carries the loose debris to the surface between the rods and the side of the hole.
▪ Provides some support to the sides of the hole if no casing is used
▪ If the depth is small and the soil stable, water alone can be used. However, drilling fluids are useful as they serve to
stabilize the bore hole.

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•Drilling mud is slurry of bentonite in water.
•The drilling fluid causes stabilizing effect to the bore hole partly due to higher specific gravity as compared with water and
partly due to formation of mud cake on the sides of the hole.
•As the stabilizing effect is imparted by these drilling fluids no casing is required if drilling fluid is used.
•This method is suitable for boring holes of diameter 10cm, or more preferably 15 to20cm in most of the rocks.
•It is uneconomical for holes less than 10cm diameter.
•The depth of various strata can be detected by inspection of cuttings.

▪ Not for gravelly soil since they keep rotating beneath drill rod

▪ Advantages :progress much faster , and disturbance of the soil below the borehole is slight.

▪ Limitations The method is not suitable if the soil contains a high percentage of gravel/cobbles, as they tend to rotate
beneath the bit and are not broken up. The natural water content of the material is liable to be increased due to contact
with the drilling fluid

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https://www.youtube.com/watch?v=mxDDX_sfEm4
https://www.youtube.com/watch?v=q5RXXvRXjlY
https://www.youtube.com/watch?v=Swgo6kHxNiA 23
4. Percussion drilling
•In case of hard soils or soft rock, auger boring or wash boring cannot be employed. For such strata, percussion drilling is usually
adopted.
•Suitable for drilling bore holes in boulderous and gravelly strata
• Here advancement of hole is done by alternatively lifting and dropping a heavy drilling bit which is attached to the lower end
of the drilling bit which is attached to the cable.
•Addition of sand increases the cutting action of the drilling bit in clays.
•Whereas, when coarse cohesionless soil is encountered, clay might have to be added to increase the carrying capacity of slurry.
• After the carrying capacity of the soil is reached, churn bit is removed and the slurry is removed using bailers and sand pumps.
•Change in soil character is identified by the composition of the outgoing slurry.
•The stroke of bit varies according to the ground condition.
•Generally, it is 45-100cm in depth with rate of 35-60 drops/min.
•It is not economical for hole of diameter less than 10cm.
•It can be used in most of the soils and rocks and can drill any material.

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•One main disadvantage of this process is that the material at the bottom of the hole is
disturbed by heavy blows of the chisel and hence it is not possible to get good quality
undisturbed samples.
•It cannot detect thin strata as well.

ADVANTAGES:
•1.percussion drilling can be used in all types of soil
•2.it is very useful for boring holes like that for tube well through rock or Boulders.
DISADVANTAGES
•1.Because of heavy blows of the chisel ,the material at the bottom is in disturbed state.
•2 More expensive as compared to other methods
•3.Diffcult to detect minor changes in the properties of the strata penetrated.
•https://www.youtube.com/watch?v=6pXuteEtuFA
5. Displacement borings
• It is combined method of sampling & boring operation.
• Closed bottom sampler, slit cup, or piston type is forced in to the ground up to the desired depth.
• Then the sampler is detached from soil below it, by rotating the piston, & finally the piston is released or withdrawn.
• The sampler is then again forced further down & sample is taken.
• After withdrawal of sampler & removal of sample from sampler, the sampler is kept in closed condition & again used for
another depth.
Features :
•Simple and economic method if excessive caving does not occur. Therefore not suitable for loose sand.
•Major changes of soil character can be detected by means of penetration resistance.
•These are 25mm to 75mm holes.
•It requires fairly continuous sampling in stiff and dense soil, either to protect the sampler from damage or to avoid
objectionably heavy construction pit.

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6. Continuous sampling
•The sampling operation advances the borehole and the boring is accomplished entirely by taking samples continuously.
•The casing is used to prevent the caving in soils.
•It provides more reliable and detail information on soil condition than the other methods.
•Therefore it is used extensively in detailed and special foundation exploration for important structures.
•It is slower method and more expensive than intermittent sampling.
•When modern rotary drilling rigs or power driven augers are not available, continuous sampling may be used to Advantage
for advancing larger diameter borings in stiff and tough strata of clay and mixed soil.
•In the Boston district, corps of Engineers has made faster progress and reduced cost by use of continuous sampling in
advancing 3-inch diameter borings through compact gravelly glacial till, which is difficult to penetrate by any boring method.

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Choice of Method:
a) Nature of Ground:
Soils – For clayey soils : borings for deep exploration and pits for shallow exploration.
•For sandy soils, boring is easy but special equipment such as, Bishop or Osterberg piston samplers, should be used
for taking undisturbed samples below the water table.
Rocks - Borings are suitable in hard rocks and pits in soft rocks.
•Core borings are suitable for the identification of types of rocks
•NX bore hole camera is useful to photograph the stratification in drilled bore holes
b) Topography
•Steeply inclined strata and slopes are most effectively explored by drifts or inclined borings and low dipping strata or
gentle slopes by trial pits or vertical borings.
•Swamps and areas overlain by water are best explored by borings which may have to be put down from floating craft.
c) Cost
For deep exploration, borings are usual as deep shafts are costly. For shallow exploration in soil, the choice between pits
and borings will depend on the nature of the ground and the information required for shallow exploration in rock; the cost of
bringing a core drill to the site will only be justified, if several holes are required; otherwise trial pits will be more economical.
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SOIL SAMPLING : Soil sampling is the method of collecting in–situ soil sample by different method in view

of performing laboratory investigation to determine engineering/index properties of soil.

SAMPLES : In geotechnical engineering soil sample is collected to learn about the properties of the strata

below the ground surface .

SAMPLER : Device used for sampling are known as soil samplers.

SOIL SAMPLING
•Sample collected are to understand the engineering characteristics of subsoil and determination of reliable information
about subsoil.
•Depending upon the process involved in collecting the soil sample during the field investigation, there can be partial to
major disturbance in the sample in comparison to its natural state.
•Based on the extent of disturbance, a sample may or may not be useful for determining inherent strength properties of
in-situ soil and determination or bearing capacity.

Type of soil samples

Disturbed sample (DS)
Representative sample
Non-representative sample
Undisturbed sample (UDS)
Need for sampling
• Sampling is carried out in order that soil and rock description, and laboratory testing can be carried out.
• Laboratory tests typically consist of:
Index tests (for example, specific gravity, water content)
Tests to determine engineering design parameters (for example strength, compressibility, and permeability).
Factors to be considered while sampling soil
Samples should be representative of the ground from which they are taken.
They should be taken in such a way that they have not lost fractions of the in situ soil.
 Natural soil structure modified or
disturbed

Used to test index properties (grain

Disturbed
size, plasticity, Specific gravity )

samples Represent composition and

mineral structure

Natural soil str. And moisture

content maintained

Engg. Properties determined (Shear

Undisturbed
str., compressibility, permeability)

Represents the soil structure

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Disturbed Sample
A soil sample in which due to disturbance caused while sampling, there are partial to full
modification of natural structure if the soil is classified as disturbed sample.
 Moisture content are lost, but the soil particles are intact.
 It can be used for grain size analysis, liquid and plastic limit, specific gravity, compaction tests, moisture content,
organic content determination and soil classification test performed in the lab
Representative sample:
•A sample which retains some mineral composition of actual soil deposit when obtained from boring but retain
information about soil structure.
•Such sample can be used for soil classification and determination of index properties of soil.
Non- representative sample:
•Samples which does not even contain mineral composition of actual soil and are collected during much disturbance
(e.g samples obtained from precussion and wash boring).
•Such sample can be used to assess change in strata as well as for qualitative assessment of soil.
•Such samples do not give specific properties of actual soil layer.
Undisturbed sample
•Undisturbed soil samples are those in which the in-situ soil structure and moisture content are preserved.
•It is almost impossible to collect any sample without a little disturbance.
•Sample collected with minimal disturbance are called as “Undisturbed”.
•Samples obtained from sampler tube or the one obtained during “trial pits”.
•Such samples can be used to determine characteristics of soil layers such as Shear strength, consolidation
behavior etc. which are useful even in foundation design.
•Difficult to collect incase of cohesion less soil.

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 How soil is disturbed??

• Soil disturbance can occur during drilling, during sampling, during transportation and storage, or during preparation for
testing.
• Any sample of soil being taken from the ground, transferred to the laboratory, and prepared for testing will be subject
to disturbance.
• The mechanisms and causes associated with this disturbance can be classified as follows:
1. changes in stress conditions;
2. mechanical deformation;
3. changes in water content and voids ratio;
4. chemical changes.
5. Volume disturbance.
6. Side friction between the sampler and the soil.
7. Loss of hydraulic pressure.
8. Working environment.
9. Improper shearing of the sample.
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10.Failure to shut-off the drilling fluid during sampling operation
 Design Features affecting the sample disturbance (IS 1892 : 1979)

The degree of disturbance is controlled by the following three features of its design :

a) Cutting edge- Inside Clearance, Outside Clearance, Area ratio

b) Inside wall friction

c) Non-return value

d) Others: Recovery Ratio, Method of applying force, Sizes of sampling tubes

Cutting edge Inside wall friction

Design features
affecting degree of
disturbance

Method of applying force Non-return valve

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1. CUTTING EDGE

(i) Inside Clearance: Ci = (D3-D1)/D1 X100

(i) Internal dia of cutting edge must be slightly less than internal dia of sampling tube

(ii) It allows elastic expansion of the sample when it enters the tube and reduces
frictional drag the sample. It reduces friction between the soil sample and the
sampler when the soil enters the tube by allowing for elastic expansion

For undisturbed sample, Ci = 0.5* to 3%

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(ii) Outside clearance: Co =(D2 – D4)/D4 X 100

▪ Outside dia of cutting edge must be more than outer dia

of tube

▪ To facilitate the withdrawal of sampler from soil, this must

be least, i.e. it help to reduce friction while the sampler is
being driven and when it is being withdrawn.

▪ For reducing the driving force, co should be as small as

possible.

▪ For undisturbed sample, It should lie between 0 to 2%

• ( But Co must not be much more than Ci)

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 2 2 2
(iii). Area ratio Ar = (D2 - D1 )/D1 X100
▪ Ar= Ratio of Maximum cross-sectional area of the cutting edge to total area of the soil sample

▪ Should be as low as possible, consistent with strength requirement of sample tube

▪ Should be < 20% for stiff formations & <10 % for sensitive clays

▪ Generally, for Undisturbed samples: Area ratio must be 10% or less than 10%

The thicker the wall of the sampling tube, the greater the
disturbance.

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2. Inside wall Friction: The inside wall should be smooth .
Can be done by:
▪ Applying oil inside the tube
▪ Providing smooth finish to sample tube
▪ Ensuring suitable inside clearance

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3. Non return Valve:
•The sampler must have a large orifice to allow quick escaping of air, water or slurry.

•It should close immediately when the sampler is with drawn

4. Others: Method of applying force:

•The degree of disturbance depends upon the method of applying force during sampling & rate of
penetration of sample.

•The sampler must be pushed not driven

Recovery ratio:
For a satisfactory undisturbed sample, taking into consideration the influence of the inside clearance when
excess soil is prevented from entering the tube, the recovery ratio calculated as follows should be between 98
and 96 percent.

R=L/H
L = length of the sample within the tube,
H = the depth of penetration of the sampling tube.
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❖ R = 1, Good recovery
❖ R<1 Sample is compressed
❖ R>1 Sample has swelled

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44
Types of Samplers

Open tube sampler

Cohesive Split spoon sampler

Piston sampler

Top controlled

samplers Bottom controlled

cohesionless
Solidification by
chemicals or emulsions
Cores
rocks Rotary drilling
washout

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Cohesive: Open tube sampler/ Shelby tubes (IS 2132- 1986)

• Thin-walled seamless steel tube of diameter 50 or 75mm and

length of 600-900mm

• The bottom end of the tube is sharpened.

• The tubes can be attached to drilling rods.

• The drilling rod with the sampler attached is lowered to the

bottom of the borehole and the sampler is pushed into the soil.

• The soil sample inside the tube is then pulled out.

• The two ends of the sampler are sealed and sent to the lab.

• The samples can be used for consolidation or shear tests.

• Suitable in very soft to medium soft clays and silts

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1

3 4

2
Open tube sampler/ Shelby tubes (IS 2132- 1986)

Materials:

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DIMENSIONS
There shall be 4 sizes, 40, 65, 80 and 100 mm based on internal diameter of the tube. The tolerence on all
dimensions shall be +_0.5 mm.
• The sampling tubes, cutting shoes and sampling heads shall be made as per details given in Fig. 1. The
length shall be as desired.
• cutting shoes have been so designed that these give area ratio within 10 percent, and inside clearance 1
to 3 percent.

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 PROCEDURE

Driving the Casing - Where casing is used it shall not be driven below the sampling level, and
casing pipe should be in such a way that it does not disturb the soil to be sampled.
• The hole shall be cleaned to sampling elevation using whatever method is preferred that will
ensure that the soil to be sampled is not disturbed. In saturated sandy and silty soils the drilling
equipment should be withdrawn slowly to prevent loosening of the soil around the hole.
• Where casing is used, the hole shall be cleaned out to the bottom or just below the casing. A clean-
out auger should be used to clean the bottom of the hole, when necessary.
• Bottom discharge bits shall not be permitted for clean-out purposes; side or upward discharge bits
may be permitted.
• The water level in the hole should be maintained at or above the ground water level, especially in
soils that might be disturbed by the flow of ground water into the drill hole such as sandy and silty
soils.

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Obtaining Soil Sample

• The depth of bottom of the casing, if used, below ground level and the water level
in the bore hole should be noted.
• Sampling shall be done as soon as possible after the clean-out operation and shall
not be done after an interval, for example, where a hole has been cleaned-out and
left overnight.
• The assembled sampling tube should be lowered to the bottom of the hole, and the
following information should be noted.
a) Depth of bottom of bore hole below ground level
b) Amount of penetration of the sampling tube into the soil, under the combined weight of the tube
and the rods; and
C) Water level in the bore hole.

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• The sampling tube shall then be pushed into the soil by a continuous and rapid motion. In no case the tube shall be

pushed farther than the length provided for the sample. About 50 mm shall be allowed for cuttings and sludge. A

clearance of 10 to 20 mm shall be allowed below the sampled head in the tube.

• The depth of penetration of the tube shall also be noted.

• Before pulling out the tube, at least 5 min shall be allowed to elapse after pushing the tube after which the tube shall be

turned at least for two revolutions to shear the sample off at the bottom.

• In case the equipment used for SPT is also used for driving the sampling tube, then the length of penetration shall be

limited to 50 blows.

• Samples shall be taken, by repeating the sampling procedures, at every change in stratum or at intervals not more than 1.5

m, whichever is less.

• Samples may be taken at lesser intervals if specified or found necessary. The intervals be increased to 3 m if in between

vane shear test or SPT is performed.

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Field Observations
• Water-table information including ground water level, elevations at which the drilling water was
lost, or deviations at which water under excess pressure was encountered should be recorded on the
field logs.

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Preparation for Shipment

• Upon removal of the sampling tube, the length of the sample in the tube and the length between the top of the tube and the
top of the sample in the tube shall be measured and recorded.

• The disturbed material in the upper end of the tube shall be completely removed before applying wax for sealing. The
length and type of the sample so removed should be recorded.

• The soil at the lower end of the tube shall be reamed to a distance of about 20 mm. After cleaning both ends shall be
sealed with wax applied in a way that will prevent wax from entering the sample. Wax used for sealing should not be
heated to more than a few degrees above its melting temperature. The empty space in the samplers, if any, should be
filled with moist soil, saw dust etc, and the ends covered with tight fitting caps.

• If it becomes necessary to keep the samples at the site for some time, they shall be kept in the shade. They should be kept
over a bed of sand, jute bags, saw dust, etc and covered over on top with similar material ( sand, jute bags, saw dust, etc).
The bed and top cover should be kept moist. Such bedding and top cover may also be provided at the time of shipment of
the samplers with samples
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Labelling and Shipping

• Labels giving the following information should be affixed to the tubes:

a) Tube number,
b) Job designation,
c) Sample location,
d) Boring number,
e) Sample number,
f) Depth,
g) Penetration, and
h) Gross recovery ratio

• The tube and boring numbers should be marked in duplicate.

• Duplicate markings of the boring number and sample number on a sheet which will not be
affected by moisture should be enclosed inside the tube.

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REPORT
• All data obtained during the boring and sampling operations shall be recorded in
the field as per details given:
PRO FORMA FOR RECORD OF OBSERVATIONS DURING UNDISTURBED SAMPLING OF SOILS
USING THIN-WALLED TUBE SAMPLES

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• This proforma has been made comprehensive to include all observations indicated in the
code.

• The Proforma may be modified to suit individual job conditions. Some of the items
indicated in the pro forma may not be needed when sampling from a open trial pit.

• In such a case the direction of sampling, horizontal or vertical should also he indicated.

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Split spoon samplers
▪ 3 parts:
▪ Driving shoe at bottom- 75mm long

▪ Steel tube, split longitudinally into 2 halves-450mm long

▪ Coupling at the top-150mm long

▪ Procedure:
▪ Sampler lowered to the bottom of the borehole by attaching it to the drill rod- Then driven by forcing it into the soil
by blows of a standard hammer- Sampler assembly then taken out- coupling an driving shoe removed - steel tube
split into halves- samples taken
▪ Standard penetration Test: Uses split spoon sampler Hammer 63.5Kg; height of fall 762mm.
▪ Samples generally taken at intervals of 1.53m
▪ Commonly used dia: Outside dia 50.8mm and inside dia 34.9mm=> Area ratio > 100%- highly disturbed samples

▪ When used in sand, ― spring core catcher‖ placed inside the split tube, to retain the sample.
 Split spoon samplers IS:9640-1980

▪ IS:9640-1980
▪ 3 parts:
▪ Driving shoe at bottom- 76.2 mm
long

▪ Steel tube, split longitudinally into 2

halves-457.2mm long
▪ Coupling at the top-150mm long

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 Piston sampler
▪ Consists of two separate parts, (a) the sample cylinder and
(b) the piston system;
▪ Piston fits tightly in the sampler cylinder and is actuated separately.
▪ During the driving and till the start of the sampling operation, the
bottom of the piston flush with the cutting edge of the sampler.
▪ At the desired sampling elevation, the piston fixed in to the ground and the
sampler cylinder forced independently into the ground, thus punching a
sample out of the soil.
▪ The piston prevents water and dirt from entering the tube during the
lowering operation. It also keeps the recovery ratio constant during the
punch.
▪ As the sampler tube slides past the tight fitting piston during the
sampling operation, a negative pressure is developed above the sample,
which holds back the sample during withdrawal

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Hand carved samples
▪ A cylindrical container open at both the ends is used for sampling.

▪ The soil is trimmed to shape at the bottom of the test pit

▪ One end of container is closed and inverted over the soil chunk and the soil sample is
removed using spatula

▪ This method is suitable for cohesive soil.

Scraper bucket sampler

▪ Whole assembly dug into the soil and rotated

▪ soil enters through the open slit

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Non Cohesive:
In silts and sands or soft soil strata, sampling operations are confronted with the possibility of the sample falling out of the
sampler due to lack of cohesion (specially in large dia tubes).
Control at the top of the sampler – A reduction of pressure on the sample is brought about by providing a bail valve in the
sampler head or a properly packed free or stationary piston in the sampling tube.
Control at the bottom of the sampler -
1) incorporating core retainers in the form of concealed springs, multiple flap valves, claw-shell valves in the sample shoe or
introducing core retainers attached to an auxiliary barrel pushed down the sampler after the drive; this will, however, disturb
the samples to certain extent.
2) maintenance of slight pressure below the sampler by the injection of compressed air into the space below the sampler
formed by the introduction of an auxiliary core barrel; I Bishop sampler may be used.
Solidification by the introduction of chemicals or emulsions – The solidification may be done at the bottom of the sampling
tube after driving or a sufficient volume of the strata to be sampled may be solidified before the sampling operation starts.

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PROCEDURE FOR TAKING SAMPLES
Disturbed Soil Samples

Undisturbed Soil Samples- moisture content and structure do not get altered.
Clay: Chunk and Core Samples
Chunk samples:
•Clay is exposed in excavation.
•A block of clay should be carefully removed with a sharp knife taking care that no water is allowed to come into
contact with the sample and that ‘the sample is protected from exposure to direct sun and wind.
•The chunk sample should be coated with molten wax so that the layer of wax prevents escape of moisture from the
sample.
•Chunk samples are not suitable if those are to be transported to long distances because in such cases the samples will
get disturbed in transit.
•Undisturbed samples may also be obtained by means of a sampling tube of 10 cm internal diameter provided with a
cutting edge
Core samples :
•The sampler should be lightly oiled or greased inside and outside to reduce friction.
•The sampler should be pushed into the clay by hand or by jacking and taken out very care fully.

Sand:
•Moist sand above ground-water level may be taken from natural exposures, excavations or borings by gently forcing a
sampling tube into the soil.
•Undisturbed samples of sand below ground-water table may be obtained by the use of a compressed air sampler, which
enables the sample to be removed from the ground into an air chamber and then lifted to the surface without contact with
water in the bore hole.
•Thin-walled piston sampler and bentonite or other types of drilling mud. he use of bentonite or other drilling mud
obviates the need for casing pipes with thin wall samplers.
HANDLING, PRESERVATION AND TRANSPORTATION OF SAMPLES

1. Undisturbed samples in seamless tube:

▪ Ends cut and removed (atleast 2.5cm)→wax→ fill space with saw dust→ lid

2. Undisturbed samples not in tube:

▪ Covered wholly with wax→ metal container→ tight lid→ adhesive tape

3. Disturbed:

Immediately placed in glass jar→ airtight container

4. Rocks:
▪ Label-reference no: directly on surface or tape wounded→ wrapped in paper→ box
▪ Rock core→ preserve whole core→ core box with separate compartments

▪ Store in cool and humid place

▪ Labeling important
▪ Transportation: Liner or containers placed in wooden box with separate partitions→ packed with
fillers

▪ Extrusion:
▪ Take out→ chip off wax
▪ Piston extrusion( if properly oiled)→ disturbs soft clay
▪ Support the sample
▪ Extrude in one direction → from cutting edge to top
▪ Store in cool humid place
▪ Rock: kept into box→ ensure no end to end turning

Labeling: Label placed inside lid on top

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EXAMINATION AND TESTING OF SAMPLES
Thank You!!!

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Thank You!!!

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