SOIL MECHANICS FOUNDATION ENGINEERING LABORATORY … · 2019. 8. 22. · Page 4 of 47 Jigme Namgyel...

Jigme Namgyel Engineering College

Department of Civil Engineering & Surveying

SOIL MECHANICS & FOUNDATION ENGINEERING

LABORATORY INSTRUCTION MANUAL

SEMESTER- II

Compiled By: Department of Civil Engineering & Surveying

Royal University of Bhutan

LIST OF EXPERIMENTS

• • Determination of Moisture Content using Oven Drying Method

• • Determination of In-situ density using Core Cutter Method

• • Determination of in-situ density using Sand Replacement Method

• • Determination of Specific Gravity of soil

• • Determination of Atterberg’s limits and Indices

• • Grain Size Analysis of soil

• • Standard Proctor Test (water content-dry density relation)

• • Direct Shear Test

• • Standard Penetration Test

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Soil Mechanics & Foundation Laboratory

Water Content in Soil- Oven Drying Method

Aim: To determine in-situ water content of the soil using Oven Drying Method.

This test is done to determine the water content in soil by oven drying method as per IS: 2720 (Part II) –

1973. The water content (w) of a soil sample is equal to the mass of water divided by the mass of solids.

Principle:

The principle of test is to determine the weight of a wet soil sample in a container, dry the sample along

with the container for 24 hours in a n oven and then determine the weight of the dry soil sample. The

water content of the soil (w, in percentage), is obtained from the relation

2 3

3 1

x100W W

wW W

−=

−%

Where W1 is the weight of the empty container, W2 is the weight of container with wet soil, and W3 is

the weight of container with dry soil

Figure 1. Set up for Moisture Content test

Apparatus Required:

1. Thermostatically controlled oven, maintained at a temperature of 110 ± 50 C.

2. Weighing balance with accuracy of 0.04 % of the mass of the soil taken

4. Airtight container made of non-corrodible material with lid

5. Tongs

Weighing balance Soil containers Oven

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Procedure:

1. Clean the container, dry it and weigh it with the lid (W1).

2. Take the required quantity of the wet soil specimen in the container and weigh it with the lid (W2)

3. Place the container, with its lid removed, in the oven for 24 hours maintaining a constant temperature

of 110±50 C.

4. When the soil has dried, remove the container from the oven, using tongs.

5. Find the weight ‘W3‘of the container with the lid and the dry soil sample.

The oven drying temperature of 110±50 C is suitable for most of the soils. A temperature more than

110±50 C should not be used as it breaks the crystal structure of the soil and causes evaporation of

structural water, which has properties completely different form normal water and is considered a part

of soil solids. For soils containing gypsum or other minerals, there is loosely bound water of hydration

which gets evaporated at 110O C. Hence, a lower temperature of 80O C should be used for oven-drying

such soils. Similarly, for soils containing organic matter, the oven-drying temperature should not exceed

60O C to prevent oxidation of organic matter. The only disadvantage of the method is that it takes

minimum 24 hours to know the test result.

Observations and Calculations:

An average of three determinations should be taken.

Sl. No.

Observations and Calculations

Determination No.

1 2 3

Observation

1 Container No.

2 Mass of empty container (W1) (g)

3 Mass of container + wet soil (W2) (g)

4 Mass of container + dry soil (W3) (g)

Calculations

5 Weight of water, WW= W2 – W3

6 Weight of solids, WS= W3 – W1

7 Water content, 2 3

3 1

x100W W

wW W

−=

−%

8 Average Moisture Content, w

Result:

Average Moisture Content of the soil is ………. %

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Remark:

1. A container without lid can be used, when moist sample is weighed immediately after placing the

container and oven dried sample is weighed immediately after cooling

2. As dry soil absorbs moisture from wet soil, dried samples should be removed before placing wet

samples in the oven.

Precautions:

• The wet soil specimen should be kept loosely in the metal container.

• Care should be taken to avoid over-heating of the soil specimen by maintaining the oven temperature

at 105 to 110oC.

• Dry soil specimen in the container, should be not be left uncovered before weighing as it is likely to

catch moisture from the surrounding atmosphere.

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Determination of Field Density of soil by Core Cutter Method (IS-27270-part-29)

Aim: To determine in-situ density of soil using Core Cutter Method.

Theory:

The in-situ density is defined as the bulk density of soil measured at its actual depth. By conducting this

test, it is possible to determine the field density of the soil. The moisture content is likely to vary from

time and hence the field density also. So, it is required to report the test result in terms of dry density.

Need and Scope:

This method covers the determination of the in-situ density of compacted soils by using core cutter. The

in-situ density of natural soil is needed for the determination of bearing capacity of soils, for the purpose

of stability analysis of slopes, for the determination of pressures on underlying strata for the calculation

of settlement and the design of underground structures. It is very quality control test, where compaction

is required, in the cases like embankment and pavement construction.

Apparatus Required:

1. Cylindrical core cutter, 100 mm internal diameter and 130mm long

2. Steel rammer, mass 9 kg, overall length with the foot and staff about 900mm.

3. Steel dolly, 25 mm high and 100 mm internal diameter

4. Weighing balance, accuracy 1g.

5. Palette knife

Rammer

Core Cutter

Dolly

Figure 1. Core cutter setup

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6. Straight edge, steel rule, etc.

7. Spade or Pick axe.

7. Apparatus for the determination of water content.

Procedure:

1. Determine the internal diameter and height of the core cutter to calculate to its volume (Vc).

2. Determine the weight (Wc) of the cutter to the nearest gram.

3. A small area, approximately 30 cm2 of the soil layer to be tested, is exposed and levelled.

4. The steel dolly is placed on the top of the cutter and the cutter is rammed down vertically into the

soil layer until only about 15 mm of the dolly protrudes above the surface.

5. The cutter is then dug out of the surrounding soil, care being taken to allow some soil to project

from the lower end of the cutter. The ends of the core cutter are then trimmed flat to the ends of

the cutter by means of the straight edge.

6. The cutter containing the soil is weighed to the nearest gram (WS).

7. The soil is removed from the cutter and a representative sample shall be placed in an air-tight

container and its water content (w) is determined.

8. It is necessary to repeat the experiment (at least three) and to average results, since the dry density

of soil varies appreciably from point to point.

Calculations:

1. In-situ bulk density ( ) of soil: It is determined using, ( )s c

c

W W

V

−=

where, WS is the weight of core cutter with wet soil, WC is the weight of empty core cutter, and VC is

the volume of core cutter.

2. Natural Moisture Content (w): Natural Moisture Content is calculate using, 2 3

3 1

( )

( )

W Ww

W W

−=

−

where W1 is the weight of empty can, W2 is the weight of can with wet soil, and W3 is the weight of

can with dried soil (after oven drying for 24 hours).

3. In-situ dry density ( d ) of soil: In-situ dry density is determined using (1 )

dw

=

+

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Sl. No.

Observations and Calculations Determination No.

1 2 3

Observation

1 Core cutter No.

2 Internal diameter (cm)

3 Internal height (cm)

4 Weight of empty core cutter (WC) (g)

5 Weight of core cutter with soil (WS) (g)

6 Weight of empty can (W1) (g)

7 Weight of can with wet soil (W2) (g)

8 Weight of can with dried soil (W3) (g)

Calculations

6 Volume of core cutter (VC) (cm3)

7 In-situ Bulk Density ( ) (g/cc)

8 Moisture Content (w)

9 Dry density ( d ) (g/cc)

Result:

Average In-situ Dry Density of the soil is ……..g/cc


Precautions:

• Core cutter method of determining the field density of soil is only suitable for fine grained soil (Silts

and clay). This is because collection of undisturbed soil sample from a coarse-grained soil is difficult

and hence the field properties, including unit weight, cannot be maintained in a core sample

• Core cutter should be driven into the ground till the steel dolly penetrates into the ground half way

only so as to avoid compaction of the soil in the core.

• Before lifting the core cutter, soil around the cutter should be removed to minimize the disturbances.

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Sand Replacement Method (IS-2720-PART-28)

Aim: To determine the field density of soil at a given location by sand replacement method

Theory:

Determination of field density of coarse grained soil such as gravels, stones and aggregates are not

possible by core cutter method, because it is not possible to obtain a core sample. In such situation, the

sand replacement method is employed to determine the unit weight. In sand replacement method, a

small cylindrical pit is excavated and the weight of the soil excavated from the pit is measured. Sand

whose density is known is filled into the pit. By measuring the weight of sand required to fill the pit and

knowing its density the volume of pit is calculated. Knowing the weight of soil excavated from the pit and

the volume of pit, the density of soil is calculated. Therefore, in this experiment there are two stages,

namely

• Calibration of sand density

• Measurement of soil density

Figure 1. Sand Replacement Apparatus

Apparatus Required:

1. Sand pouring cylinder

2. Calibrating can

3. Metal tray with a central hole

4. Dry sand (passing through 1 mm sieve and retained on 600 micron sieve)

5. Oven

6. Balance

7. Moisture content bins

8. Glass plate

9. Metal tray & Scraper tool

Sand pouring cylinder

Metal/Soil Tray

Calibration container

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Procedure:

STAGE-1 (CALIBRATION OF SAND DENSITY)

1. Measure the internal dimensions (diameter, d and height, h) of the calibrating can and compute its

internal volume, 2

4C

d hV

=

2. Fill the sand pouring cylinder (SPC) with sand with 1 cm top clearance (to avoid any spillover during

operation) and find its weight (W1)

3. Place the SPC on a glass plate, open the slit above the cone by operating the valve and allow the sand

to run down. The sand will freely run down till it fills the conical portion. When there is no further

downward movement of sand in the SPC, close the slit. Measure the weight of the sand required to

fill the cone. Let it be W2.

4. Place back this W2 amount of sand into the SPC, so that its weight becomes equal to W1 (As mentioned

in point-2). Place the SPC concentrically on top of the calibrating can. Open the slit to allow the sand

to run down until the sand flow stops by itself. This operation will fill the calibrating can and the

conical portion of the SPC. Now close the slit and find the weight of the SPC with the remaining sand

(W3)

STAGE-2 (MEASUREMENT OF SOIL DENSITY)

1. A flat area, approximately 450 mm2, of the soil to be tested is exposed and trimmed down to a level

surface preferably with the aid of a scraper tool.

2. Place the tray with a central hole over the portion of the soil to be tested.

3. Excavate a pit into the ground, through the hole in the plate, approximately 15 cm deep (same as the

height of the calibrating can). The hole in the tray will guide the diameter of the pit to be made in the

ground.

4. Collect the excavated soil into the tray and weigh the soil (W)

5. Determine the moisture content of the excavated soil.

6. Place the SPC, with sand having the latest weight of W1, over the pit so that the base of the cylinder

covers the pit concentrically.

7. Open the slit of the SPC and allow the sand to run into the pit freely, till there is no downward

movement of sand level in the SPC and then close the slit.

8. Find the weight of the SPC with the remaining sand (W4).

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Enter all the data as per the table given below and calculate accordingly.

Sl. no Data (Calibration of Unit Weight of Sand) Trial-1 Trial-2 Trial-3

1 Volume of the calibrating container, V (cm3)

2 Weight of SPC + sand, W1 (g)

3 Weight of sand required to fill the conical portion on a flat surface, W2 (g)

4 Weight of SPC + sand (after filling calibrating can), W3 (g)

5 Weight of sand required to fill the calibrating container, WC = (W1-W2 –W3) (g)

6 Unit weight of sand, Csand

W

V = (g/cm3)

Sl. no Data (Determination of Density of Soil) Trial-1 Trial-2 Trial-3

1 Weight of the excavated from the pit (W) (g)

2 Weight of sand + SPC, before pouring, W1 (g)

3 Weight of SPC after filling the hole & conical portion, W4 (g)

4 Weight of sand in the pit WP = (W1-W4-W2) (g)

5 Volume of sand required to fill the pit, Vp=WP/γsand (cm3)

6 Bulk unit weight of the soil γt=W/VP (g/cm3)

7 Dry unit weight of the soil γd=γ/(1+w) (g/cm3)

(where ‘w’ is the moisture content)

Result:

Average In-situ Dry Density of the soil is found ..……… g/cc

Average Moisture Content of the soil is ……….. %

Precautions:

• If for any reason it is necessary to excavate the pit to a depth other than 15 cm, the standard

calibrating can should be replaced by one with an internal height same as the depth of pit to be made

in the ground.

• Care should be taken in excavating the pit, so that it is not enlarged by levering, as this will result in

lower density being recorded.

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• No loose material should be left in the pit.

• There should be no vibrations during this test.

• It should not be forgotten to remove the tray, before placing the SPC over the pit.

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Specific Gravity Test of Soil (IS-2720-Part-3-1980)

Aim: To determine the specific gravity (GS) of soil using Pycnometer.

Theory:

The specific gravity of a soil is the ratio of the mass of a given volume of the material at a stated

temperature to the mass of an equal volume of de-aired or gas-free distilled water at a stated

temperature. The specific gravity of a soil is used in the phase relationship of air, water, and solids in a

given volume of the soil.

Need and Scope:

The specific gravity of a soil is used in relating a weight of soil to its volume and in calculation of phase

relationship, i.e. the relative volume of solids to water and air in a given volume soil. The specific gravity

is used in the computations of most of the laboratory tests, and is needed in nearly all pressure,

settlement, and stability problems in soil engineering.

Table 1. Range of GS for Different Soil Types

Soil type

Range of GS

Sand

Silty Sand

Inorganic Clay

Soils with mica or iron

Organic Soil

2.65-2.67

2.67-2.70

2.70-2.80

2.75-3.00

<2.00

Figure 1. Pycnometer

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Apparatus Required:

1. Pycnometer

2. Sieve (4.75 mm)

3. Weighing balance

4. Glass rod

Procedure:

1. Dry the pycnometer and weigh it with its cap (W1)

2. Take about 200 g to 300 g of oven dried soil passing through 4.75 mm sieve into the pycnometer

and weigh again (W2)

3. Add water to cover the soil and stir gradually till it fills the pycnometer in order to remove the air.

4. After the air has been removed, screw the pycnometer and fill it with water up to its screw cap and

weigh it (W3).

5. Remove the soil completely and clean the pycnometer by washing it thoroughly.

6. Fill the cleaned pycnometer completely with water up to its top with cap screw on.

7. Weigh the pycnometer with water (W4).

8. From data obtained determine specific gravity of the soil.

Tabulation and Results:

Data sheet for moisture content determination:

Sl. No.

Observations an Calculations

Determination No.

1 2 3

1 Weight of empty pycnometer (W1) (g)

2 Weight of pycnometer + dry soil (W2) (g)

3 Weight of pycnometer + dry soil + water (W3) (g)

4 Weight of pycnometer + water (W4) (g)

5 Specific Gravity, 2 1

2 1 3 4

( )'

( ) ( )S

W WG

W W W W

−=

− − −

6 Temperature Correction, K27 (usually taken at 27OC)

(See K27 from Table 2.)

7 Corrected Specific Gravity of soil at 27OC,

GS = G’S x K27

8 Average Corrected Specific Gravity, GS

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Result:

The average corrected specific gravity (GS) of the soil is ...........

Determine the type of soil according to your interpretations from specific gravity of the soil (Table 1)

Table 2. Correction Factor for Variation in Specific Gravity of water due to Temperature

Temperature °C K

15 1.0026

16 1.0024

17 1.0023

18 1.0021

19 1.0019

20 1.0017

21 1.0015

22 1.0013

23 1.001

24 1.0008

25 1.0005

26 1.0003

27 1

28 0.9997

29 0.9994

30 0.9991

31 0.9988

32 0.9985

33 0.9982

34 0.9979

35 0.9975

36 0.9972

37 0.9968

38 0.9964

39 0.9961

40 0.9957

Precautions:

• The soil for test should be perfectly dry.

• Cap of the pycnometer should be screwed up to the same mark for each test.

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Atterberg’s Limits for Soil Classification

A fine-gained soil can exist in any of several states; which state depends on the amount of water in the

soil system. When water is added to a dry soil, each particle is covered with a film of adsorbed water. If

the addition of water is continued, the thickness of the water film on a particle increases. Increasing the

thickness of the water films permits the particles to slide past one another more easily. The behavior of

the soil, therefore, is related to the amount of water in the system. Approximately sixty years ago, A.

Atterberg defined the boundaries of four states in terms of "limits" as follows:

Atterberg's Definitions:

• Liquid limit: The boundary between the liquid and plastic states.

• Plastic limit: The boundary between the plastic and semi-solid states.

• Shrinkage limit: The boundary between the semi-solid and solid states.

Casagrande's Definition:

These limits have since been more definitely defined by A. Casagrande as the water contents which

exist under the following conditions:

• Liquid limit: The water content at which the soil has such a small shear strength that it flows to

close a groove of standard width when jarred in a specified manner.

• Plastic limit: The water content at which the soil begins to crumble when rolled into threads of

specified size.

• Shrinkage limit: The maximum water content at which reduction in water content will not cause

decrease in the volume of the soil mass. It is therefore the lowest water content at which a soil can

still be completely saturated. It is the boundary between semi-solid and solid states.

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Liquid Limit test of soil using Casagrande’s Apparatus (IS-2720-Part-5-1985)

Aim: To determine the Liquid Limit of a given soil sample.

Theory:

When water is added to dry soil, it changes its state of consistency from hard to soft. If we add water to a

fine-grained soil, then water will change its consistency from hard to semi hard. If we continue to add

more water then again, the soil will change its state of consistency from semi hard to plastic and finally

reach a liquid consistency stage. When the soil reaches liquid consistency state, it has remained no

cohesive strength to retain its shape under its own weight. It will start to deform its shape. So, the amount

of water which is responsible for this state of consistency of soil is called liquid limit of soil. In other

words, we can define liquid limit as, “It is the minimum water content at which the soil is still in the liquid

state but has a small shearing strength against flow.”

From test point of view, we can define liquid limit as, “Liquid limit is defined as the minimum water

content at which a pat of soil cut by a groove of standard dimension will flow together for a distance of

12 mm (1/2 inch) under an impact of 25 blows in the device.”

Apparatus Required:



3. Moisture cans

4. Sieve [425 micron]

5. Casagrande apparatus

6. Spatula

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Preparation of sample

After receiving the soil sample, it is dried in air or in oven (maintained at a temperature of 600C). If clods

are there in soil sample then it is broken with the help of wooden mallet. The soil passing 425-micron

sieve is used in this test.

Procedure:

1. About 120 gm. of air dried soil from thoroughly mixed portion of material passing 425 microns IS

sieve is obtained.

2. Water is mixed to the soil thus obtained in a mixing disc to form uniform paste. The paste shall have

a consistency that would require 30 to 35 drops of cup to cause closer of standard groove for

sufficient length.

3. A portion of the paste is placed in the cup of Casagrande’s device and spread into portion with few

strokes of spatula.

4. It is trimmed to a depth of 1 cm at the point of maximum thickness and excess of soil is returned to

the dish.

5. The soil in the cup is divided by the firm strokes of the grooving tool along the diameter through the

center line of the follower so that clean sharp groove of proper dimension is formed.

6. Then the cup is dropped by turning crank at the rate of two revolutions per second until two halves

of the soil cake come in contact with each other for a length of about 12 mm by flow only.

7. The number of blows required to cause the groove close for about 12 mm is recorded.

8. A representative portion of soil is taken from the cup for water content determination.

9. The test is repeated with different moisture contents at least 3 times for blows between 10 and 40.

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Data sheet for moisture content determination:

Sl. No.


Determination No.

1 2 3

Observation

1 Container No.

2 Weight of empty container (W1) (g)

3 Weight of container + wet soil (W2) (g)

4 Weight of container + dry soil (W3) (g)

Calculations




3 1

x100W W

wW W

−=

−%


9 Number of Blows, N

Interpretation:

A ‘flow curve’ is to be plotted on a semi-logarithmic graph representing water content in arithmetic scale

and the number of drops on logarithmic scale.

The flow curve is a straight line drawn as nearly as possible through four points

The moisture content corresponding to 25 blows as read from curve is the liquid limit of that soil.

The liquid limit (LL) of the soil sample is ………. %.

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PLASTIC LIMIT TEST IS: 2720 (Part 5) – 1985 (Reaffirmed-2006)

Aim: To determine the plastic limit of the soil sample.

Theory:

The plastic limit (PL) is determined by rolling out a thread of the fine portion of a soil on a flat, non-porous

surface. The plastic limit is defined as the moisture content where the thread breaks apart at a diameter

of 3.2 mm (about 1/8 inch). A soil is considered non-plastic if a thread cannot be rolled out down to 3.2

mm at any moisture.

Need & Scope:

Plastic Limit (PL or WP) is the water content in percent, of a soil at the boundary between the plastic and

semi-solid states. Soil is used for making bricks, tiles and soil cement blocks in addition to its use as

foundation for structures. The plastic limit of soils is also used extensively either individually or together

with other soil properties to correlate with engineering behavior such as compressibility, permeability,

compactability, shrink - swell and shear strength.

Apparatus Required:



3. Moisture cans

4. Sieve [425 micron]

5. Glass plate for rolling the soil specimen

6. Spatula

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Procedure:

1. Take 20 gm of oven-dried soil, passed through 425-micron sieve (In accordance with I.S. 2720: part-

1), into an evaporating dish. Add water/distilled water into the soil and mix it thoroughly to form

uniform paste (the soil paste should be plastic enough to be easily molded with fingers).

2. Prepare several ellipsoidal shaped soil masses by squeezing the soil between your fingers. Take one

of the soil masses and roll it on the glass plate using your figures. The pressure of rolling should be

just enough to make thread of uniform diameter throughout its length. The rate of rolling shall be

between 60 to 90 strokes per min.

3. Continue rolling until you get the thread diameter of 3 mm.

4. If the thread does not crumble at a diameter of 3 mm, knead the soil together to a uniform mass and

re-roll.

5. Continue the process until the thread crumbles when the diameter is 3 mm.

6. Collect the pieces of the crumbled thread for moisture content determination. (Prepare threads at

least with 10gm of soil for water content measurement).

7. Repeat the test at least 3 times and take the average of the results calculated to the nearest whole

number as Plastic Limit.

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An average of three determinations should be taken as plastic limit

Sl. No.


Determination No.

1 2 3

Observation

1 Container No.




Calculations




3 1

x100W W

wW W

−=

−%


Result:

The Plastic limit (PL) of the soil is ………. %

Remark:

The Plasticity Index (IP = LL-PL) of the soil is ………. %

Soil Classification using Plasticity Chart using obtained Liquid Limit (LL) and Plasticity

Index (IP)

Way forward:

1. Plot the plasticity chart.

2. Record the Plasticity Index obtained from the experiment (IP).

3. Record the Plasticity Index obtained from the chart (IC).

4. If (IP<IC), the coordinates of Liquid Limit and Plasticity Index lies below A-Line.

5. If (IP>IC), the coordinates of Liquid Limit and Plasticity Index lies above A-Line.

6. Mark the coordinates in the plasticity chart and classify the soil.

Interpretation:

The soil sample is classified as ……………

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Safety & Precautions:

3. Soil used for liquid limit determination should not be oven dried prior to testing.

4. In LL test the groove should be closed by the flow of soil and not by slippage between the soil and the

cup.

5. After mixing the water to the soil sample, sufficient time should be given to permeate the water

throughout out the soil mass.

6. Wet soil taken in the container for moisture content determination should not be left open in the air,

the container with soil sample should either be placed in desiccators or immediately be weighed.

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Sieve Analysis of Soil (IS-2720-Part-4-1980) Reaffirmed 2006

Aim: To determine particle size distribution of soil.

Theory:

Soil gradation (sieve analysis) is the distribution of particle sizes expressed as a percent of the total dry

weight. Gradation is determined by passing the material through a series of sieves stacked with

progressively smaller openings from top to bottom and weighing the material retained on each sieve.

Figure 1. Sieve Analysis Setup

Need & Scope:

The results of testing will reflect the condition and characteristics of the aggregate from which the sample

is obtained. Therefore, when sampling, it is important to obtain a disturbed representative sample that

is representative of the source being tested because the distribution of different grain sizes affects the

engineering properties of soil.

Apparatus Required:

5. A series of sieve sets ranging from 4.75mm to 75μm

(4.75 mm, 2.00 mm, 1.00 mm, 425 μm, 212 μm, 150 μm, 75 μm)

6. Weighing Balance

7. Sieve shaker

Procedure:

9. Take 500 gm of the soil sample after taking representative sample by quartering.

10. Conduct sieve analysis using a set of standard sieves as given in the data sheet.

Sieves and Sieve Shakers Grain Size Distribution after Sieving

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11. The sieving may be done either by hand or by mechanical sieve shaker for 10 minutes.

12. Weigh the material retained on each sieve

13. The percentage retained on each sieve is calculated on the basis of the total weight of the soil sample

taken.

14. From these results the percentage passing through each of the sieves is calculated.

15. Draw the grain size curve for the soil in the semi-logarithmic graph provided.

16. Obtain percentage retention for gravel, sand (coarse, medium and fine) and silt-clay fraction.

17. Calculate Co-efficient of uniformity (CU) and Co-efficient of curvature (CC) from GSD curve.

18. Classify the soil as per Indian Soil Classification System (IS:1948-1970)

Tabulation:

Data sheet for Sieve Analysis:

Weight of Sample taken for Sieve Analysis = ______ gms.

I.S. sieve size (BSS or

ASTM) Sieve size (if used)

Wt. of sieve (g)

Wt. of soil retained

(g)

Percent (%) weight

retained

Cumulative percent

retained (%)

Percent (%) weight passing

4.75 mm

2.00 mm

1.00 mm

425 microns

300 microns

150 microns

75 microns

Pan

Result:

Plot Grain Size Distribution curve and complete the table

D10: D30: D60:

Sl. No. Attributes Data

1 Percentage of Gravel (>4.75mm)

2 Percentage of Sand (4.75mm – 0.075mm)

3 Percentage of Silt-Clay fraction (<0.075 mm)

4 Co-efficient of Uniformity (CU)

5 Co-efficient of Curvature (CC)

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Reaffirming to Indian Soil Classification System (IS:1948-1970), hence the soil is classified as

……………………………

Precautions:

• While drying the soil, the temperature of the oven should be about 105 to 110 degree Celsius, as

higher temperature may lead to some organic changes in the material finer than 75 micron.

• During shaking soil sample should not b allowed to spell out.

• All the readings should be noted carefully.

• Clean the sieves set so that no soil particles are struck in them

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Compaction Test- (Standard Proctor Compaction)

(IS 2720-PART VII-1980) Reaffirmed-2011

Aim: To determine the Maximum Dry Density and Optimum Moisture Content of soil sample

Theory:

In geotechnical engineering, soil compaction is the process in which a stress applied to a soil causes

densification as air is displaced from the pores between the soil grains. It is an instantaneous process and

always takes place in partially saturated soil (three phase system). The Proctor compaction test is a

laboratory method of experimentally determining the optimal moisture content at which a given soil type

will become most dense and achieve its maximum dry density. It determines relationship between the

moisture content and density of soils compacted in a mould of a given size with a 2.5 kg rammer dropped

from a height of 30 cm. The results obtained from this test are helpful in increasing the bearing capacity

of foundations, decreasing the undesirable settlement of structures, controlling undesirable volume

changes, reduction in hydraulic conductivity, Increasing the stability of slopes, etc.

Figure 1. Laboratory Compaction test equipment

Rammer

Mould with collar and

base plate

I.S. Sieve

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Apparatus Required:

10. Compaction mould

11. Rammer, mass 2.6 kg

12. Detachable base plate and collar

13. IS Sieve, 4.75 mm

14. Oven

15. Weighing Balance, 1g accuracy

16. Moisture content bins

17. Graduated Cylinder

18. Scraper tool, Spatula, Metal tray, etc.

Procedure:

9. Approximately 5 kg of soil passing through 4.75 mm sieve is thoroughly mixed with known water

content. Thoroughly mix the sample with sufficient water to dampen it with approximate water

content. For fine grained soil, 8-10% of water and for coarse soil, 4-5% of water is added to given soil

sample.

10. Clean and dry the mould and the base plate. Grease them lightly.

11. Weigh the proctor mould without base plate and collar

12. Attach the collar to the mould. Place the mould on a solid base.

13. Place the soil in the Proctor mould and compact it in 3 layers giving 25 blows per layer with the 2.5

kg rammer falling through. The blows shall be distributed uniformly over the surface of each layer.

14. The top surface of the first layer be scratched with spatula before placing the second layer. The

second layer should also be compacted by 25 blows of rammer. Likewise, place the third layer and

compact it.

15. The amount of the soil used should be just sufficient to fill the mould ad leaving about 5 mm above

the top of the mould to be struck off when the collar is removed.

16. Remove the collar and trim off the excess soil projecting above the mould using a straight edge.

17. Remove the base plate and the collar. Weigh with mould with soil to the nearest gram.

18. Remove the soil from the mould. The soil may also be ejected out.

19. Take the soil samples for the water content determination from the top, middle and bottom

portions. Determine the water content.

20. Add about 3% of the water to a fresh portion of the processed soil, and repeat the steps 4 to 11.

Continue this series of determination until there is either a decrease or no change in the wet unit

weight of the compacted soil

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Enter all the data as per the table given below and calculate accordingly.

Sl. No.


Determination No.

1 2 3 4 5

Observation

1 Container No.




Determination of Moisture Content




3 1

x100W W

wW W

−=

−%

4 Average Moisture Content, w (%)

Determination of Dry Density

Sl. No.


Determination No.

1 2 3 4 5

Observation

1 Diameter of mould (cm)

2 Height of mould (cm)

3 Volume of the mould (V) (cm3)

4 Weight of empty mould (W1) (g)

5 Weight of mould + compacted soil (W2) (g)

6 Specific Gravity of soil (GS)

7 Unit weight of water, ( w ) (g/cc)

Calculation

1 Weight of compacted soil, W= W2 – W1

2 Bulk density, = W/V (g/cc)

3 Average Moisture Content, w (%)

4 Dry density (1 )

dw

=

+(g/cc)

5

Dry density at 100 % saturation (ZAVL)

,max

(1 )

s wd

s

G

G w

=

+ (g/cc)

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Make a plot between dry density as ordinate and moisture content as abscissa on a simple graph paper as

shown in Fig. 2. Plot the ZAVL (Zero Air Void Line) in the same graph. The coordinates of the peak of the curve

give the Maximum Dry Density (MDD) and Optimum Moisture Content (OMC) of the soil.

Result:

Maximum Dry Density of the soil (from plot), ..……… g/cc

Optimum Moisture Content (from plot) ……….. %

Precautions:

• Ramming should be done continuously taking care of height of 310 mm free fall accurately. The blows

should be uniformly distributed over the surface of each layer of soil compaction.

• Scratch each layer of the compacted soil with a sharp tool before pouring the soil for next layer.

• The amount of soil taken for compaction should be in such a way that after compacting the last layer, the

soil surface is not more than 5 mm above the top rim of the mould.

• Weighing should be done accurately.

• During compaction, the mould should be keeper over a solid base.

0

0.5

1

1.5

2

2.5

0 5 10 15 20 25 30

Dry

den

sity

(g

/cc)

Water content, w (%)

Compaction Curve

OMC

MDD ZAVL (S = 100%)

Figure 2. Compaction Curve

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Direct Shear Test (IS-2720-PART-13-1986) Reaffirmed-2002

Aim: To determine the shear strength parameters of cohesionless soil

Theory:

The shear strength of a soil mass is its property against sliding along internal planes within itself. The

stability of slope in an earth dam or hills and the foundations of structures built on different types of soil

depend upon the shearing resistance offered by the soil along the possible slippage surface. Shear

parameters are also used in computing the safe bearing capacity of the foundation soils and the earth

pressure behind retaining walls. The shear strength is determined using the following equation:

tanS c = +

Where S = Shear strength of soil (kg/cm2)

c = Cohesion (kg/cm2)

σ = Normal stress (kg/cm2)

ϕ = Angle of shearing resistance (degrees)

The parameters ‘c’ and ‘ϕ’ for a particular soil depend upon its degree of saturation, density and the

condition of laboratory testing. In a direct shear test, the sample is sheared along a horizontal plane. This

indicates that the failure plane is horizontal. The normal stress (σ) on this plane is the external vertical

load divided by the area of the soil sample. The shear stress at failure is the external lateral load divided

by the corrected area of soil sample. The principle of the test is to cause shear failure of a soil specimen,

place in a shear box along a predetermined horizontal plane, under a given normal stress, and to

determine the shear stress at failure. The test is repeated on identical soil specimens under different

normal stresses and the shear stress at failure under each normal stress is determined. A graph is plotted

between the normal stress and the shear stress and the y-intercept and the slope of the failure envelope

so obtained are taken as the shear parameters ‘c’ and ‘ϕ’, respectively.

The main advantage of direct shear apparatus is its simplicity and smoothness of operation and the

rapidity with which testing programmes can be carried out. But this test has the disadvantage that lateral

pressure and stresses on planes other that the plane of shear are not known during the test.

Need & Scope:

The value internal friction angle and cohesion of the soil are required for design of many engineering

problems such as foundations, retaining walls, bridges, sheet piling. Direct shear test can predict these

parameters quickly.

Apparatus Required:

8. Shear box and shear box container

9. Base plate with cross groves on its top

10. Porous stones (2 nos. )

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11. Plain Grid plates (2 nos. )

12. Perforated grid plates (2 nos. )

13. Loading pad with steel ball

14. Digital weighing machine

15. Loading frame with loading yoke

16. Weights

17. I.S Sieve 4.75 mm, Tampering Rod, Spatula, Rammer, Sampler, etc.

Procedure:

19. Shear box dimensions is measured, the box is set up by fixing its upper part to the lower part with

clamping screws, and then a porous stone is placed at the base. Conduct sieve analysis using a set of

standard sieves as given in the data sheet.

20. For undrained tests, a serrated grid plate is placed on the porous stone with the serrations at right

angle to the direction of shear. For drained tests, a perforated grid is used over the porous stone.

21. A desired amount of soil is sieved through 4.75 mm sieve.

22. The soil is placed into the shear box in three layers and for each layer is compacted with a tamper.

The upper grid plate, porous stone and loading pad is placed in sequence on the soil specimen.

23. Weigh the shear box to compute the weight of soil used for the test. Calculate the density of the soil.

24. The box is placed inside its container and is mounted on the loading frame. Upper half of the box is

brought in contact with the horizontal proving ring assembly. The container is filled with water if

soil is to be saturated.

25. The clamping screws is removed from the box, and set vertical displacement gauge and proving ring

gauge to zero.

26. The vertical normal stress is set to a predetermined value. For drained tests, the soil is allowed to

consolidate fully under this normal load. (Avoid this step for undrained tests.)

27. The motor is started with a selected speed and shear load is applied at a constant rate of strain.

Readings are taken until the horizontal shear load peaks and then falls, or the horizontal

displacement reaches 20 % of the specimen length.

28. The moisture content of the specimen is determined after the test. The test is repeated on identical

specimens under different normal stress values.

29. The test is repeated with three normal stresses of 100, 200 and 400 kN/m2.

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Dial gauge

Weights to apply

normal stress

Proving Ring

Figure 1. Direct Shear Test apparatus

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Observation and Calculations:

Data sheet for Direct Shear Test:

Area of the Specimen = ______ cm2.

Test No. Normal Load (kg) Shear Load at Failure (kg)

Normal Stress (kg/cm2)

Shear Stress at Failure (kg/cm2)

1

2

3

4

Make a plot between Shear Stress as ordinate and Normal stress as abscissa on a simple graph paper as

shown in Fig. 2. The y-intercept gives the cohesion or unit cohesion (c) while the slope gives the angle of

internal friction or angle of shearing resistance (ϕ).

Result:

The unit cohesion (c ) of the soil is ………. kg/cm2

The angle of shearing resistance (ϕ) of the soil is ……… kg/cm2

0

1

2

3

4

5

6

7

8

9

0 1 2 3 4 5 6 7

Shea

r S

tres

s, k

g/c

m2

Normal Stress, kg/cm2

c

ϕ

Figure 2. Failure Envelope

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Precautions:

• The dimensions of the shear box should be measure accurately.

• Before allowing the sample to shear, the screw joining the halves of the box should be taken out.

• Rate of strain or shear displacement rate should be constant throughout the test.

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Standard Penetration Test

Aim: To perform standard penetration test and obtain the bearing capacity for a given site using

IS Code Method (IS: 6403-1981).

Apparatus Required:

1. Tripod (with 4m clear height and one of the legs of the tripod should have ladder to facilitate a person

to reach tripod head).

2. Tripod head with hook.

3. Pulley

4. Guide pipe assembly (with 75cm clear travel of the standard 63.5kg weight and provision to connect

to A-drill extension rods)

5. Standard spilt spoon sampler (inner diameter is 38 mm and outer diameter 50 mm)

6. A-drill rods

7. Heavy duty post hole auger (100 mm to 150 mm diameter)

8. Heavy duty helical auger

9. Manila rope

10. Casing pipe

11. Measuring tape

Theory:

Standard Penetration Test (SPT) is a standard method of sounding (I.S 2131; ASTM D1586). SPT is a

widely used method for determining the in-situ parameters of the soil. This test conducted by means of

a split spoon sampler furnishes dependable and reproducible data about the resistance of soils to

penetration. The number of blows (N-values) per 15 cm penetration of a standard split spoon sampler,

using a specified dry weight assembly, is widely used for determining the bearing capacity (for

cohesionless strata) and other important in situ parameter of the sub soil strata.

In this test, a thick wall standard slit spoon sampler, 50.8mm outer diameter and 35mm inner diameter

is driven into the undisturbed soil at the bottom of the borehole under the blow of a 63.5kg drive weight

with a 75cm free fall. The minimum open length of the sampler should be 60cm. The number of blows

required to drive the sampler 30cm beyond the seating drive of 15cm is termed as penetration resistance,

(N).

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Figure 1. Drive Weight Assembly for SPT

Figure 2. Details of Split Spoon Sampler

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Figure 3. Extraction of Soil Sample from SPT

Test Pit

SPT assembly

Soil Sample from sampler

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The N-value observed during the test is not utilized directly in assessing the soil properties, instead these

values are corrected to account for:

1. The overburden pressure

From several investigations, it is proven that the penetration resistance or the value of N is dependent

on the overburden pressure. If there are two granular soils with relative density same, higher ‘N’ value

will be shown by the soil with higher confining pressure. With the increase in the depth of the soil, the

confining pressure also increases. So the value of ‘N’ at shallow depth and larger depths are

underestimated and overestimated respectively. Hence, to account this the value of ‘N’ obtained from the

test are corrected to a standard effective overburden pressure.

2. Dilatancy in saturated fine sands and silts

Silty fine sands and fine sands below the water table develop pore water pressure which is not easily

dissipated. The pore pressure increases the resistance of the soil and hence the penetration number (N).

Essential Parameters:

a. Relative Density ( DR ) and Compactness, are determined from Table. 1 given by Terzaghi and

Peck through interpolation.

Table 1. Relationship of N and ϕ to relative Density for cohesionless soil

N & ϕ related to Relative Density for cohesionless soil ( Terzaghi & Peck)

N- corrected Relative Density (DR) ϕ (Degree) Compactness

0-4 0-15 < 28 Very loose

4-10 15-35 28-30 Loose

10-30 35-65 30-36 Medium

30-50 65-85 36-41 Dense

> 50 > 85 > 41 Very Dense

b. Overburden Pressure ( PO ) is given by PO = ( unit weight of soil x depth ) expressed in kg/cm2

c. Correction for overburden pressure is calculated by calculating a correction factor ( CN ) and

multiplying with the observed N-values from the test.

N 10

O

20C =0.77log

P for PO 0.25 kg/cm2

Therefore, Corrected N-value due to overburden (N’) = CN N,

Where N’ = Corrected N-value due to overburden

CN = Correction factor for overburden pressure

For PO 0.25 kg/cm2, correction factor ( CN ) should be obtained from the given graph.

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d. The value obtained in (c) should also be corrected for dilatancy, if the sub soil level (at which the

test is made) consists of find sand and silt and the sub soil level exists below water table.

Correction is applied as below only to the N’ (Corrected N value) more than 15.

Correction for dilatancy (N’’) = 15+0.5 (N’-15), (if N’ 15, then N’’=N’)

e. The cumulate average of above corrected N-value i.e. N’’ is correlated with the graph given below

to find the angle of shearing resistance (ϕ).

Note: The N-value in the following graph should be read as N’’

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f. By obtaining the ϕ -value, bearing capacity factors such as Nc, Nq and Ny can be assessed through

Vesic’s expression.

• 2tan 452

PK

= +

• ( 1)cotc qN N = −

• tan

q PN K e =

• 2( 1) tanqN N = +

g. Cohesion (c) is obtained from the undrained compressive strength derived from Table 2 using

the relation i.e. c = Undrained Compressive Strength/2

Table 2. SPT and Consistency of Clay

N values

Consistency

Consistency

Index

Undrained Compressive Strength (kg/cm2)

0-2 Very soft 0.5 <0.25

2-4 Soft 0.5-0.75 0.25-0.5

4-8 Medium 0.5-0.75 0.5-1.0

8-16 Stiff 0.75-1.0 1.0-2.0

16-32 Very Stiff 1.0-1.5 2.0-4.0

>32 Hard >1.5 >4.0

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I.S. Code Method for finding the Bearing Capacity of Shallow Founation

IS: 6403-1981 recommends the following equation for the net ulimate bearing capacity of shallow

foundations:

( 1) 0.5 'nu c c c c q q q qq cN S d i q N S d i BN S d i W = + − +

Where q is the effective pressure at the base i.e. γDf and W’ is the water table correction factor

Note:

• If the water table is at deth (Df+B) or below from the ground surface, the value of W’ is taken as 1.0.

• If the water table is likely to rise to the base of the footing or above, the value of W’ is taken as 0.5.

• If the water table is at a depth below the base of foundation but leass that B below the base of

foundation, the value of W’ is taken by linear interpolation between 0.5 and 1.0.

The shape factors Sc , Sq , Sγ depend on the shape of the footing and are different for square, circular and

rectangular footings. The deductions are made base on the followng table.

Shape Factors

Sl.No.

Shape of footing

Shape Factor

Sc Sq Sγ

1 Continuous Strip 1.00 1.00 1.00

2 Rectangle 1+0.2B/L 1+0.2B/L 1-0.4B/L

3 Square 1.3 1.2 0.8

4 Circle 1.3 1.2 0.6

Where B and L are the the Width of footing

Depth factors are as follows:

• 1 0.2c p

Dd K

B= +

• 1 for <10qd d = =

• 1 0.1 for 10q p

Dd d K

B = = +

IS: 6403-1981 recommends that the depth factors dc, dq, dγ shall be applied only when backfilling is

done with proper compcation. Otherwise the depth factor will be equal to 1.

Inclination factors are as follows:

•

2

190

c qi i

= = −

•

2

1i

= −

Where α is the angle of inclination of load with vertical (usully taken as 1)

Net Ultimate Bearing Capacity is obtained by using the expression given by I.S. Code Method.

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The Net Safe Bearing Capacity (qns) is found by qns = qnu/F where F is the factor of safey usually taken as

2.5 or 3 for shallow foundation.

Similary Safe Bearing Capacity (qs)is found by qs = qns+ γDf

Procedure:

1. Identify the location of testing in the field.

2. Erect the tripod such that the top the tripod head is centrally located over the testing spot. The legs

of the tripod should form the equilateral triangles.

3. Advanced the borehole at the test location-using auger.

4. Clean the split spoon sampler and apply a thin film of oil to the inside face of the sampler. Connect A-

drill extension rod to the split spoon sampler.

5. Slip the 63.5kg weight onto the guide pipe assembly to the other end of the A-drill rod.

6. The chain connected to the driving weight (63.5 kg) is tried to the manila rope passing over the pulley

at the tripod head. The other end of the rope is pulled down manually to vertically erect the set up.

7. Mark the straight edge level (ground level) all around the A-drill rod with the help of chalk or any

other marker. From this mark, measure up along A-drill rod and mark 15cm, 30cm, and 45cm above

the straight edge level.

8. Lift the weight 63.5kg up to guide pipe assembly and allow the weight to fall freely from the height

75cm.

9. Count the number of blows required for the first 15cm, second 15cm and the third 15cm mark to

cross down the straight edge.

10. The penetration of a 15cm is considered as the seating drive and the number of blows required for

this penetration is noted but not accounted in computing penetration-resisting value.

11. Advance the bore hole by another 1m (i.e. the depth of penetration of the sampler, 45cm+55cm) or

till a change of strata whichever is early.

12. The test is repeated with the advancement of bore hole till the required depth of exploration is

reached or till a refusal condition is uncounted (refusal condition is said to exist if the no. of blows

required for the last 30cm of penetration is more than 100). The depth of exploration depends on the

required bearing capacity, depth of foundation and width of foundation. Generally, the depth of

exploration is twice the width of the foundation below the foundation level.

13. Obtain the corrected N-value i.e. N’’ with essential corrections (overburden & dilatancy corrections)

over the obtained N-value.

14. Determine the angle of internal friction (ϕ) from the Graph. 2. and determine the bearing capacity

factors (Nc, Nq and Ny)

15. Determine the cohesion with reference to Table. 2.

16. Assume a suitable shape and size of the footing.

17. Determine the shape, depth and inclination factors

18. Using the I.S. Code Method, Calculate the Net Ultimate, Net Safe and Safe Bearing Capacity of the

shallow foundation.

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DETERMINATION OF PHYSICAL PROPERTIES OF EXTRACTED SOIL FROM TEST PITS

1. Water Content (w)

This test is performed to determine the water content in soil by oven drying method as per IS: 2720

(Part II) –1973. The water content (w) of a soil sample is equal to the mass of water divided by the

mass of solids. it is usually expressed as percentage of the dry mass using the following equation i.e.

Water Content (w) = x 100W

S

W

W=

Where Ww = Weight of water in soil mass, Ws = Weight of dry soil

Sl. No. Particulars Depth of Penetration

0 - 0.45 m 0.45 - 0.90 m

TEST PIT:

1 Weight of wet soil (W1) (g)

2 Weight of dry soil (W2) (g)


4 Water Content (w) (%)

5 Average Moisture Content ( w )

2. In-situ Density (γ)

Depth of Penetration

Sl. No. Particulars 0 - 0.45 m 0.45 - 0.90 m

TEST PIT:

1 Weight of soil (W) (g)

2 Length of extracted sample (L) (cm)

3 Internal dia. of sampler (d) (cm)

4 Volume of the sample (V) (cm3)

5 In-situ density (γ) (g/cc)

6 Average In-situ density (γ) (g/cc)

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OBSERVATION AND CALCULATION SHEET FOR STANDARD PENETRATION TEST

Depth (m)

Observed N value

Corrected N value after overburden correction

(N’)

Corrected N value after Dilatancy correction

(N’’)

Final Corrected N-Value

(N’’) ϕ

Relative Density

1.50 N/A N/A N/A N/A N/A N/A

1.95

2.40

Client: Location: Date:

Test Pit:

Soil Classification System: Indian Standard Soil Classification System

Observation Calculated For cohesionless soil

Depth Penetration Blows Corrected N-values

In-situ density

Overburden pressure

Moisture Content

Relative Density

Angle of

Internal Friction

Co

mp

actn

ess

(m) (mm) (Number) (N’’) (g/cc) (kg/cm2) (%) (%) (ϕ)

1.50 0-150

150-300

1.95 300-450

0-150

150-300

2.40 300-450

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CALCULATION SHEET FOR STANDARD PENETRATION TEST

Shape of Footing:

Sl. No. Particulars Values

1 Length of Footing (L) (cm)

2 Width of Footing (B) (cm)

3 Depth of Footing (Df) (cm)

4 In-situ Density (γ) (g/cc)

5 Cohesion (c) (kg/cm2)

6 Angle of Internal Friction (ϕ)

7

Bearing Capacity Factors

NC

Nq

Nγ

8

Shape Factors

SC

Sq

Sγ

9

Depth Factors

dC

dq

dγ

10 Inclination Factors

ic

iq

iγ

11 Water Table Correction (W’)

12 Net Ultimate Bearing Capacity (qnu) (kg/cm2)

13 Net Safe Bearing Capacity (qns) (kg/cm2)

14 Safe Bearing Capacity (qs) (kg/cm2)

Result:


Average In-situ density of the soil is ………….. g/cc

The calculated safe bearing capacity of the soil is (qs)= ……………. ( kN/m2) (Expressed in kilopascal (kPa)

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Precautions:

• If the test is to be carried out in gravely soils, then the driving shoe is replaced by solid 60-degree

cone.

• If the test is carried out in very fine sand or silty sand below the water table the measured “N” value

if greater then 15, should be corrected for the increased resistance excess more water pressure set

up during driving and unable to loose immediately.

• Stop dropping weight, when the sample penetrates less than 25 mm under 50 blows.

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