TYPES OF FOUNDATION AND COFFERDAM

LECTION OF FOUNDATION
MADE BY : MISS.DHARA DATTANI
(ME TRANSPORTATAION)
LECTURER AT ATMIYA INSTITUTE OF TECHNOLOGY AND
SCIENCE FOR DIPLOMA STUDIES,RAJKOT.GUJRAT,INDIA.
PART-1
1

What s Foundation ?
• Every building consists of two basic components :
1. The Super-structure
2. The Sub-structure
• The substructure or foundation is that part of the structure which is usually
below the ground level and in direct contact with the soil , through which the
load of superstructure is transmitted to the soil.
• The basic function of a foundation is to transmit the dead loads, superimposed
loads and wind loads from a building (superstructure) to the soil in such a way
that:
a. Settlements are uniform and within permissible limit. &
b. The soil does not fail. 3

Functions of Foundations :
1. Reduction of load intensity.
Foundations distribute the load of the superstructure to a larger area so the total
intensity of load doesn't exceed the safe bearing capacity of soil.
2. Even distribution of load.
Foundations distribute the non uniform load of the super structure evenly to the
subsoil.
3. Provision of level surface.
Foundations provide a levelled and hard surface over which a super-structure can
be built.
4. Lateral stability.
It anchors the super-structure to the ground thus imparting stability to the building.
5. Safety against undermining.
It provides safety against undermining or scouring due to burrowing animals &
flood water.
6. Protection against soil movements.
Special measures prevent or minimise the distress (cracks) in superstructure, due
to expansion or contraction of sub-soil.
4

ESSENTIAL REQUIREMENTS FOR A GOOD
FOUNDATION
 The foundation shall be constructed to sustain load and transmit these to
subsoil in such a way that pressure on it will not cause settlement which
would impair the stability of the building.
 Foundation should be rigid so that the differential settlements are
minimised.
 Specially for the case when superimposed loads are not evenly distributed.
 Foundations should be taken sufficiently deep to guard the building against
damage or distress caused by swelling or shrinkage of sub-soil.
 Foundations should be so located that its performance may not be affected
due to any unexpected future influence.
5

• Types of Foundation
Shallow Foundation Deep Foundation
(A) Shallow Foundation: According to Terzaghi, a foundation is shallow if its
depth is equal to or less than its width. (D<B)
(B) Normally shallow foundation used upto 5m depth.also called open
foundation
• Types of Shallow Foundation:
 Spread footing
 Combined footing
 Strap Footing
 Mat Foundation or Raft Foundation
 Grillage Foundation
6

• Spread Footing/ Isolated column:-Spread footings are those which
spread the super-imposed load of wall or column over larger area.
Spread footing support either column or wall.
• It may be following kinds
• Stepped footing for column: This type of footing provided for heavily
loaded column which required greater spread with steps. The base is
generally made of concrete. Used in wall/column
• Sloped footing for column: In this type of footing concrete base does
not have uniform thickness but is made sloped. Generally used when
sbc is low and hard strata is not found.
• Wall footing without step: It consist of concrete base without any steps
including masonry wall.
• Stepped footing for wall: It consist of masonry wall have stepped
footing with concrete base .
7

• Grillage Foundation
• It is special type of isolated footing generally provided for heavily loaded
steel column and used in those location where bearing capacity of soil is
poor.
• The depth of such foundation is limited to 1 to 1.5 m.
• This type of arrangement avoids deep excavation and provide necessary area
at the base to reduce the intensity of pressure.
9

Combined Footing:
• A spread footing which supports two or more columns is termed as combined
footing.
• When two column are so close to each other that tier individual footing would
over lap.
• The combined footing may be of following kinds.
• Rectangular combined footing: The combined footings will be provide in
rectangular in shape if columns carry equal loads. The design of rectangular
combined footing should be done in such way that centre of gravity of column
coincide with centroid of footing area.
• Trapezoidal combined footing: If columns carry unequal loads the footing is of
trapezoidal shape are provided.
• Combined column-wall footing: It may be required to provide a combined
footing for column and wall. Such combined footing are shown in fig.
11

Strap Footing:
• It is a Independent footing of two columns are connected by a beam, it
is called a strap footing.
• The strap connects the two footings such that they behaves as one
unit.
• The strap does not remain in contact with soil and does not transfer
any pressure to the soil.
• A strap footing is more economical than a combined footing.
• Also used when the distance between two column is large.
14

Raft foundation:
 A raft Foundation is a combined footing that covers the entire
area beneath a structure and support all the wall and column.
 When the allowable soil pressure is low.
 When the structure loads are heavy
 When there is a large variation in the loads on individual
columns.
 When foundation of soil is non homogeneous and there are
chances of differential settlements.
16

Deep foundation
• Deep foundation are those in which the depth of foundation is very
large in comparison to its width.(D>B).
Deep foundation may be of following types
• Pile foundation
• Pier foundation
• Caissons or Well foundation
18

• Pile Foundation
• Pile Foundation is that type of foundation in which the
loads are taken to a low level by means of vertical
members which may be timber, concrete or steel.
• Pile foundation may be adopted when no firm bearing
strata is available and the loading is uneven.
• Piles may be of following types
• End bearing piles
• Friction Pile
• Compaction pile
Prepared By : Mr. Mayank M. Parekh 19

• End bearing piles: This types of piles are used to
transfer load through water or soft soil to a
suitable bearing stratum.
• Friction Pile: Friction piles are used to transfer
loads to a depth of friction load carrying material
by means of skin friction along the length of piles.
• Compaction pile: Compaction piles are used to
compact loose granular soils, thus increasing their
bearing capacity.
20

• Pier foundation:
• A Pier foundation consist of cylindrical
column of large diameter to support and
transfer large superimposed load to the firm
strata below.
• Generally, pier foundation is shallow in depth
than the pile foundation.
22

• Well Foundation:
• Well Foundation or Caisson are box like
structures which are sunk from the surface of
either land or water to the desired depth.
• They are much larger than the pier foundation
or drilled caissons.
• Caisson foundations are used for major
foundation works like
• Bridge piers
• Docks
• Large water front structure such as pump
house.
24

Coffer dams:
• A cofferdam is a
temporary structure
which is built in a river,
lake etc. to remove water
from an area and make it
possible to carry on the
construction work under
reasonably dry
conditions.
• Cofferdams are usually
required for project such
as dams and construction
of piers and abutment.

Requirement of a cofferdam :-
• The cofferdam should be reasonably watertight.
• It should be generally constructed at site of work.
• The design and layout of a cofferdam should be such that the
total cost of construction, maintenance and pumping is
minimum.
• It should be stable against bursting, overturning and sliding,
under the floods and waves.
• The water to be excluded by a coffer dam may be either
ground water of water lying above ground level, it may be
deep or shallow and still or running.
• The materials used in construction of a cofferdam are earth,
timber, steel and concrete.

Necessity of cofferdam :-
 The coffer dams are required in the following situation:
• When it is required to construct a structure in the river bad.
• When structure is to be constructed on a sea shore.
• When it is required to construct a structure one a bank of the
lake or inside the lake.
• When deep excavation are carried out in a course grained soil.
• When excavation is carried out below ground water table.
• During deep excavation, when sides of the trenches are likely
to collapse.

Use of cofferdam
• To facilitate pile driving operation
• To place grillage and raft foundation
• To construct foundations for piers and abutments of
bridge, dams, locks, etc.;
• To enclose a space for the removal of sunken vessels
• To provide a working platform for the foundation of
building when water is met with; and
• To provide space for carrying out the foundation work
without disturbing or damaging the adjoining structure
such as buildings, pipelines, sewers, etc.

Types of cofferdam :-
• Earthen cofferdam
• Rock-filled cofferdams
• Sand bags cofferdam
• Single wall cofferdams
• Double wall cofferdams
• Cellular cofferdam

Earthen cofferdam :-
• This is the simplest form of cofferdam. It essentially consist
of an earthen embankment built around the area to be
enclosed.
• Suitable for low, 1.2 to 1.5 m and moderate head of water.
• The top of embankment should be 1m above the water
level.

Rock-filled cofferdams :-
• Suitable for turbulent flow and up to 3m depth of water.
• Stone or rubble is used for the embankment.
• It construction is adopted only the stone is easily available
in the nearby areas.

Sand bags cofferdam :-
• The method of
using laminated
sand bags to build
cofferdam are
easy to construct,
cost-efficient and
economic friendly

Single wall cofferdams
• This type of
cofferdam is used in
places where the
area to be enclosed
is very small and the
depth of water is
more, say 4.5 to 6 m.
• It can be used for up
to 25m depth of
water.

Double wall cofferdams :-
 Two-parallel rows of steel
sheet piles driven into the
ground
 Tied together with anchors
and wales, then filled with
soil
 There are two types of this
type of cofferdams:
1. ohio river type wood
sheeting cofferdam
2. Wood or steel sheeting
cofferdam with wales and
tie rods

Cellular cofferdams :-
• Circular cells are connected by
diaphragms
• Deep excavations
• Used when the construction
area is very large
• Also used when internal
bracing is impractical
• There are two types of this
type of cofferdams:
1. Circular
2. Diaphragm

• Foundations on Black Cotton Soil
• Black cotton soils and other expansive soils have typical characteristics of
shrinkage and swelling due to moisture movement through them.
• When moisture enter between the soil particles under some hydrostatic pressure,
the particles separate out, resulting in increase in the volume.
• This increase in volume is commonly known as swelling. If this swelling is
checked or restricted high swelling pressure, acting in the upward direction, will
be induced.
• This would result in several cracks in the walls and may some times damage the
structural such as lintels, beams, slabs etc.
• During summer season, moisture moves out of the soil and consequently, the soil
shrinks.
• Shrinkage cracks are formed on the ground surface. These shrinkage cracks
some times also known as tension cracks, may be 10 to 15 cm wide on the
ground surface.
• Black cotton soils and other expansive soils are dangerous due to their shrinkage
and swelling characteristics.
• In addition, these soils have very poor bearing capacity, ranging from 5 t/m2 to
10 t/m2.
38

• For designing footings on these soils, the following points should be kept in mind:
• 1. The safe bearing capacity should be properly determined, taking into account the
effect of sustained loading. The bearing capacity of these soils may be limited to 5 to
10 t/m2.
2. The foundation should be taken at least 50 cm lower than the depth of moisture
movement.
3. Where this soil occurs only in top layer, and where the thickness of this layer does
not exceed 1 to 1.5 m, the entire layer of black cotton soil should be removed, and
the foundation should be laid on non-shrinkable non- expansive soil.
5. Where the soil is highly expansive, it is very essential to have minimum contact
between the soil and the footing. This can be best achieved by transmitting the loads
through deep piles.
6. Where the bearing capacity of soil is poor, or soil is very soft, the bed of the
foundation trench should be made firm or hard by ramming mooram.
39

Types of foundation in black cotton soils.
Foundation in black cotton soils may be of the following types:
1. Strip foundation. For medium loads, strip foundation may
be provided, along with special design features.
2. Pier foundation Piers are dug at regular interval and filled
with cement concrete. The piers may rest on good bearing
strata.
3. Under-reamed pile foundation. An under-reamed pile is a
pile of shallow depth (1 to 6 m) having one bulb at its lower
end.
40

• Under-reamed Pile Foundation
• Under-reamed piles are bored cast-in-situ concrete piles
having bulk shaped enlargement near base.
• These piles are commonly recommended for providing safe
and economical foundations in expansive soils such as black
cotton soil having poor bearing capacity.
• In these type of foundation the structure is anchored to the
ground at a depth where ground movement due to changes in
moisture content negligible.
• A pile having one bulk is known as single under-reamed pile.
It is seen that the load bearing capacity of the pile can be
increased by increasing the number of bulk at the base.
• In such a case the pile is named as multi-under-reamed pile.
The increase in the bearing capacity of the pile can also be
achieved by increasing the diameter and the length of the pile.
41

• The method of construction of under-reamed pile is very simple.
The holes for casting piles in the ground may be bored by using
hand augers.
• After boring is carried out at the required depth, the base of the
bore hole is enlarged in the form of a bulb near its base by use of a
tool, known under-reamer.
• After the pile holes are ready for concreting, reinforcement cage are
lowered in the holes and concrete is poured.
• The piles should be cast at least 200 to 400 mm above the cut-off
level. Later on, when the concrete is hardened, the extra length of
each pile is broken and the pile top is brought to the desired level.
• Thus, besides relative saving in direct cost (when compared with
conventional isolated footings) it is possible to have overall saving
in time of completion of a work by adopting under-reamed piles.
42

Prepared By : Mr. Mayank M. Parekh 43

Part 2: SUBSOIL EXPLORATION…
44

Definition
•The process of determining the layers of
natural soil deposits that will underlie a
proposed structure and their physical
properties is generally referred to as site
investigation.
• The field and laboratory studies carried out
for obtaining the necessary information about
the sub soil characteristics including the
position of ground water table are termed as
soil exploration
45

METHODS OF EXPLORATION
1. Preliminary exploration
Local topography, excavations, cuttings, drainage
pattern and other natural features like streams,
flood marks etc.
Geophysical methods
2. Detailed investigation
Nature, sequence and thickness of layers. Borings and
detailed sampling, in-situ test.

OBJECTIVES OF SITE INVESTIGATION
1. Site selection.
2. Foundation and earthworks design.
3. Temporary works design.
4. The effects of the proposed project on its
environment.
5. Investigation of existing construction.
6. The design of remedial works.
7. Safety checks.

EXPLORATION PROGRAM
The purpose of the exploration program is to
determine, within practical limits, the
stratification and engineering properties of the
soils underlying the site.
The principal properties of interest will be the
strength, deformation, and hydraulic
characteristics. The program should be planned
so that the maximum amount of information can
be obtained at minimum cost.
48

The general objective of an exploration program is to identify all
of the significant features of the geologic environment that
may impact on the proposed construction.
Specific objectives are to:
1. Define the lateral distribution and thickness of soil and rock
strata within the zone of influence of the proposed
construction.
2. Define groundwater conditions considering seasonal changes
and the effects of construction or development extraction.
3. Identify geologic hazards, such as unstable slopes, faults,
ground subsidence and collapse, floodplains, regional
seismicity, and lahars.

4. Procure samples of geologic materials for the
identification, classification, and measurement of
engineering properties.
5. Perform in situ testing to measure the engineering
properties of the geologic materials

The purpose of a soil investigation program
1. Selection of the type and the depth of foundation suitable for a
given structure.
2. Evaluation of the load-bearing capacity of the foundation.
3. Estimation of the probable settlement of a structure.
4. Determination of potential foundation problems (for example,
expansive soil, collapsible soil, landfill, and so on).
5. Establishment of ground water table.
6. Prediction of lateral earth pressure for structures like retaining
walls, sheet pile bulkheads, and braced cuts.
7. Establishment of construction methods for changing subsoil
conditions.
51

If only they had proper site investigation…
52
…Tower of Pisa will not be leaning today!

Depth of Boring
1. Determine the net increase of stress, under a foundation
with depth as shown in the Figure.
2. Estimate the variation of the vertical effective stress, ', with
depth.
3. Determine the depth, D = D1, at which the stress increase 
is equal to (1/10) q (q = estimated net stress on the
foundation).
4. Determine the depth, D = D2, at which /' = 0.05.
5. Unless bedrock is encountered, the smaller of the two depths,
D1 and D2, just determined is the approximate minimum depth
of boring required. Table shows the minimum depths of
borings for buildings based on the preceding rule.
53

Depth of Boring
54
Determination of the minimum depth of boring

Building
width
Number of Storeys
1 2 4 8 16
Boring Depth
30.5 3.4 6.1 10.1 16.2 24.1
61 3.7 6.7 12.5 20.7 32.9
122 3.7 7 13.7 24.7 41.5

Depth of Boring
When deep excavations are anticipated, the depth
of boring should be at, least 1.5 times the depth
of excavation. Sometimes subsoil conditions are
such that the foundation load may have to be
transmitted to the bedrock. The minimum depth
of core boring into the bedrock is about 3m. If the
bedrock is irregular or weathered, the core
borings may have to be extended to greater
depths.
56

Spacing Boring
There are no hard and fast rules for the
spacing of the boreholes. The following
table gives some general guidelines for
borehole spacing. These spacing can be
increased or decreased, depending on the
subsoil condition. If various soil strata are
more or less uniform and predictable, the
number of boreholes can be reduced.
59

SOIL BORING
The earliest method of obtaining a test hole was to
excavate a test pit using a pick and shovel.
Because of economics, the current procedure is to
use power-excavation equipment such as a
backhoe to excavate the pit and then to use hand
tools to remove a block sample or shape the site
for in situ testing. This is the best method at
present for obtaining quality undisturbed samples
or samples for testing at other than vertical
orientation.
61

1. Holding verically and pressing it down while the
auger is rotated
2. Fills annular space
3. Upto depth of 6m in soft soils with or with out
casing
4. Samples are highly disturbed
5. For shallow foundaion, highways .etc
SHELL and AUGER method is widely used in india.

1. Water is forced under
pressure through a
hollow drill which may
be rotated or moved up
and down inside casing
2. Lower end has
chopping bit
Only boring can be done
and sample of no use
/ Wash boring

1. Breaking up the formation by repeated blows of
heavy bit or chisel inside casing pipe
2. Limited water forming slurry of pulverized material
and removed using bailer
3. Cables in place of drill rods

1. Cutting action of rotating
bit –kept in contact with
the bottom of hole
2. (Bentonite) Drilling mud is
used
3. Core-barrel with diamond
bits for rock cores

c) Sub-surface sounding
• The sounding method consists of measuring the resistance of the soil with the
depth by the means of penetrometer under static and dynamic loading.
• The penetrometer may consist of sampling spoon or cone or any other shaped
tool.
• The resistance to penetration is correlated with some engineering properties of
soil such as density index, consistency, bearing capacity etc.
• Thus in this method by using sounding , the resistance of soil is measured
which is useful for general exploration of erratic soil profiles , for finding depth
to bed rock or stratum.
• We can have an approximate induction of strength and other properties of soil.
• The two commonly used tests are standard penetration test and the cone
penetration test.
75

d) Geo Physical Methods
• Geo physical methods are used when the depth of exploration is very large, and
also when the speed of investigation is of primary importance.
• Geo physical investigations involve the detection of significant differences in
the physical properties of geological formations.
• The most commonly used methods of geophysical investigation are :
1. Seismic Refraction Method :
• The seismic refraction method is based on the property of seismic waves to
refract (or be bent) when they travel from one medium to another of different
density or elasticity.
• In this method, shock waves are created into the soil at their ground level or a
certain depth below it.
• The radiating shockwaves are picked up by the vibration detector (Geophone or
seismometer) where the time of travel of shock waves get recorded.
77

• Direct waves or primary waves travel directly from shock point along the ground
surface to be picked up by geophone.
• Refracted waves travel through the soil and also get refracted at the interface of two soil
strata. The refracted waves are also picked up by the geophone.
• If the underlying level is denser the refracted waves travel much faster and at longer
distances, the shock waves reach faster than the direct waves.
• Hence by distance-time graphs and analytical methods, the depth of various strata can
be evaluated by using the time of travel of primary and refracted waves.
• Seismic refraction method is fast & reliable in establishing the profile of different
strata.
• Different material such as gravel, clay hardpan or rock have characteristic properties
and hence can be identified by distance-time graphs.
• But for exact recognition and exploration, boring or sounding methods should be
supplemented along. 78

2. Electrical resistivity method
• The electrical resistivity method is based on the measurement and recording of changes
in the mean resistivity of various soils.
• Each soil has its own resistivity depending upon its composition , compaction, water
content etc.
• In this method , four metal spikes serve as electrodes which are drive into the ground
along a straight line at equal distance.
• A direct voltage is imposed between the outer two electrodes, and potential drop is
measured between the inner electrodes.
• The mean resistivity Ω (ohm-cm) is calculated by : Ω = 2 Π D E / I
D = Distance between electrodes. (cm)
E = Potential drop between inner electrodes. ( volts)
I = Current between outer electrodes. (ampere)
• The depth of exploration is roughly proportional to the electrode spacing .
• So to study greater depths, the electrode spacing is increased gradually and made
roughly equal to depth of exploration required. This method is know as resistivity
sounding.
81

Preparation of Boring Logs
1. Name and address of the drilling company
2. Driller’s name
3. Job description and number
4. Number, type, and location of boring
5. Date of boring
6. Subsurface stratification, which can he obtained by visual observation of
the soil brought out by auger, split-spoon sampler, and thin-walled
Shelby tube sampler
7. Elevation of water table and date observed, use of casing and mud losses,
and so on
8. Standard penetration resistance and the depth of SPT
9. Number, type, and depth of soil sample collected
10. In case of rock coring, type of core barrel used and, for each run, the
actual length of coring, length of core recovery, and RQD
83

SOIL SAMPLING
1. Two types of soil samples can be obtained during sampling
disturbed and undisturbed.
2. Reasonably good estimates of properties for cohesive soils
can be made by laboratory tests on undisturbed samples
which can be obtained with moderate difficulty.
3. It is nearly impossible to obtain a truly undisturbed sample of
soil; so in general usage the term "undisturbed" means a
sample where some precautions have been taken to
minimize disturbance or remolding effects.
4. In this context, the quality of an "undisturbed" sample varies
widely between soil laboratories.
86

Disturbed vs Undisturbed
• Disturbed samples are those where the natural soil
structure gets modified or destroyed during the
sampling operation.
• Natural moisture content and proportion of mineral
constituents are preserved
• “Representative samples”-useful in identification and
are partially deformed. The engineering properties
are changed, but the original fabric and structure
vary from unchanged to distorted, and are still
apparent. Such distortion occurs with split-barrel
samples.

• “Non-representative samples”- Alteration in original soil
structure,soils from other layers gets mixed up or the
mineral constituents gets altered
Extent of sample disturbance
• Cutting edge
• Inside wall friction
• Non-return valve
1) Inside clearance Ci=((D3-D1)/D1)x100
2) Outside clearance Co= ((D2-D4/D4)x100
3) Area ratio Ar= ((D2
2-D1
2)/D1
2)x100

• Inside clearance
1. Reduce friction between the soil sample and the
sampler when the soil enters, by allowing for elastic
expansion. If too large, there will be too much lateral
expansion
2. Should be between 1 to 3 percent
• Outside clearance
Reduce friction while sampler is being driven and when it is
being withdrawn after sample is collected
1. Not greater than inside clearance
2. Lies between 0 and 2 percent

• Area ratio
1. Kept as low as possible
2. Not greater than 20 percent for stiff formations and 10
percent for soft sensitive clays
Index of sample disturbance
Recovery ratio ,Lr=
𝑅𝑒𝑐𝑜𝑣𝑒𝑟𝑒𝑑 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑠𝑎𝑚𝑝𝑙𝑒
𝑃𝑒𝑛𝑒𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑡ℎ𝑒 𝑠𝑎𝑚𝑝𝑙𝑒𝑟
• Lr=1
• Lr<1
• Lr>1

• Undisturbed samples-Original soil structure is
preserved and the material properties have not
undergone any alteration or modification.
• Undisturbed samples may display slight deformations
around their perimeter, but for the most part, the
engineering properties are unchanged. Such results
are obtained with tube or block samples.
• However an undisturbed sample may be considered
as one of in which the material has been subjected
to such a small disturbance that it is still suitable for
all lab test like shear strength and consolidation

(%)100
..
....
2
22



DI
DIDO
AR
92
Good quality samples necessary.
AR<10%
sampling tube
soil
area ratio
Thicker the wall, greater the disturbance.

SPLIT SPOON SAMPLER
• Split-Barrel Sampler (Split Spoon) (ASTM D1586-99)
Purpose
• Split-barrel samplers are used to obtain representative
samples suitable for field examination of soil texture and
fabric and for laboratory tests, including measurements
of grain size distribution, specific gravity, and plasticity
index, which require retaining the entire sample in a
large jar.

Sampler Description
• Split-barrel samplers are available with and without
liners; A common O.D. is 51mm and I.D 35mm. with ¼ in.
wall thickness (1½ in. sample). Larger diameters are used
for sampling gravelly soils. Lengths are either 18 or 24 in.
• A ball check valve prevents drill pipe fluid from pushing
the sample out during retrieval. To prevent sample
spillage during retrieval, flap valves can be installed in the
shoe for loose sands, or a leaf-spring core retainer
(basket) can be installed for very soft clays and fine
cohesion-less soils. Upon retrieval, the barrel between
the head and the shoe is split open, the sample is
examined and described, removed, and stored.

• In some sampler types, brass liners are used for
procuring drive samples of strong cohesive soils for
laboratory direct-shear testing.
Sampling Procedure
• The sampler is installed on the hole bottom, then driven
into the soil with a hammer falling on the drill rods. The
number of blows required for a given weight and drop
height, and a given penetration, are recorded to provide
a measure of soil compactness or consistency as in
Standard Penetration Test.

Thin-Wall Tube Samplers
Purpose
• Thin-wall tube samplers are used to obtain UD of soft to
stiff cohesive soils for laboratory testing of strength,
compressibility, and permeability.
Tube Materials
• Cold-drawn, seamless steel tubing (trade name “Shelby
tube”) is used for most soil materials; brass tubes are
used for organic soils where corrosion resistance is
required. Lacquer coating can provide corrosion
protection and reduce internal frictional resistance and
sample disturbance. and sample disturbance.

• Tube diameters and lengths range from 2 to 6 in. in diameter,
24 to 30 in. in length. 2 in. diameter samples have a large
ratio of perimeter disturbance to area and are considered too
small for reliable laboratory engineering-property testing.
• The tube should be provided with a cutting edge drawn in to
provide inside clearance (or 0.5 to 3% less than the tube
I.D.), which permits the sample to expand slightly upon
entering the tube, thereby relieving sample friction along the
walls and reducing disturbance.
• Tubes 4 to 6 in. in diameter reduce disturbance but require
more costly borings.
• Outside dia- 40 to 125mm
• Tickness 1.25 mm to 3.15mm
• Length- 5 to 10 times dia for sandy soil and 10 to 15 times dai
for clay

Operations
• Thin-wall tubes are normally pressed into the soil by
hydraulically applied force. After pressing, the sample is
left to rest in the ground for 2 to 3 min to permit slight
expansion and an increase in wall friction to aid in
retrieval. The rods and sampler are rotated clockwise
about two revolutions to free the sampler by shearing
the soil at the sampler bottom.
• The sample is withdrawn slowly from the hole with an
even pull and no jerking. In soft soils and loose granular
soils, the sampler bottom is capped just before it
emerges from the casing fluid to prevent the soil from
falling from the tube.

Shellby Tube Sampling
• A thin-wall tube is fitted to a head assembly that is attached
to drill rod. An “O ring” provides a seal between the head
and the tube, and a ball check valve prevents water in the
rods from flushing the sample out during retrieval.
Application is most satisfactory in firm to hard cohesive soils.
• Care is required that the sampler is not pressed to a
distance greater than its length.
• Soft soils are difficult to sample and retain because they
have insufficient strength to push the column of fluid in the
tube past the ball check valve. In stiff to hard cohesive soils,
samples are often taken by driving heavy-gage tubes.

ROCK SAMPLING - Definition
105

Rock Quality Designation
106
RQD
Rock Quality Designation (RQD) is defined as the percentage of rock cores that have
length equal or greater than 10 cm over the total drill length.

FIELD STRENGTH TESTS
The following are the major field tests for
determining the soil strength:
1. Vane shear test (VST).
2. Standard Penetration Test (SPT).
3. Cone Penetration Test (CPT).
4. The Plate Load Test (PLT).
107

Standard Penetration Test (SPT)
108

109

Standard penetration test IS 2131-
1963
• Useful in determining the relative density and the angle
of shearing resistance of cohesion-less soils
• Also can find the compressive strength of cohesive soils
• Test is conducted in BH using split spoon sampler
• Drop hammer of weight 63.5 kg falling from a height of
75cm
• First 15 cm seating drive
• Number of blows required for next 30 cm penetration
was noted-SPT number
• Test is discontinued if the number of blows exceed 50

Corrections are normally applied to the SPT blow
count to account for differences in:
• energy imparted during the test (60%
hammer efficiency)
• the stress level at the test depth
The following equation is used to compensate for
the testing factors (Skempton, 1986):
111

112

SPT Correlations in Granular Soils
113
(N)60 Dr (%) consistency
0-4 0-15 very loose
4-10 15-35 loose
10-30 35-65 medium
30-50 65-85 dense
>50 85-100 very dense

•  = 28+0.15RD (degrees)
• it can vary 2
114

SPT Correlations in Clays
115
N60 cu (kPa) consistency visual identification
0-2 0 - 12 very soft Thumb can penetrate > 25 mm
2-4 12-25 soft Thumb can penetrate 25 mm
4-8 25-50 medium Thumb penetrates with moderate
effort
8-15 50-100 stiff Thumb will indent 8 mm
15-30 100-200 very stiff Can indent with thumb nail; not
thumb
>30 >200 hard Cannot indent even with thumb
nail
Use with caution; unreliable.

Cone penetration test
• Cone test was developed by Dutch government. Hence known as
Dutch cone test
• “IS: 4968 (Part-III)-1976—Method for subsurface sounding for
soils—Part III Static cone penetration test”.
• Static method or dynamic method
• STATIC METHOD
1. Cone is pushed downward by applying thrust at a steady rate of
10mm/sec through a depth of 35mm each time-Cone resistance
2. Cone is withdrawn and the sleeve is pushed on to the cone and
both are pushed together.-Combined resistance
3. Sleeve resistance-Combined resistance-Cone resistance

• Results of SCPT is compared with SPT
• Gravels- qc= 800N to 1000N
• Sands-qc= 500N to 600 N
• Silty sands qc= 300 N to 400 N
• Silts and Clayey silts qc- 200N
N is the SPT number

Cone Penetration Test (CPT)
119
Apex angle 60o
Diameter 35.7 mm

120

127

128

Type of clay Cone factor
Normally consolidated 11 – 19
Over consolidated
At shallow depth 15 to 20
At large depth 12 to 18

TYPES OF FOUNDATION AND COFFERDAM

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