Sm lab manual

Parul Institute of Technology, Limda.Department of Civil Engineering

LAB MANUALSOIL MECHANICS

(2150609)Vth Sem.

Soil Mechanics Lab Manual - 1 -- 1 -

Prepared By Nirali B. Hasilkar & Bhavita S. DaveAssist. Prof., PIT, Limda.


SOIL MECHANICSINDEX

Pract. No.

Name of Practical Date Sign

1 PROCTOR COMPACTION TEST

2 CBR TEST

3 CONSOLIDATION / OEDOMETER TEST

4 DIRECT SHEAR TEST

5 INCONFINED COMPRESSION TEST

6 DEMONSTRATION OF TRIAXIAL TEST

7 AUGER BORING / SAMPLING

8 FREE SWELL AND SWELL POTENTIAL




EXPERIMENT NO: 1

PROCTOR COMPACTION TEST




PROCTOR COMPACTION TEST DATE:

AIM OF THE EXPERIMENT:

To determine the Optimum moisture content and maximum dry density of a soil by standard proctor compaction test.

APPARATUS REQUIRED:a) Special:

I. Proctor mould (capacity 1000.0 cc, internal diameter 100mm, and effective height 127.3 mm.

II. Rammer for light compaction (2.6Kg, with free drop of 310 mm).III. Mould accessories including detachable base plate, removable Collar.IV. I.S. sieve 4.75 mm.

b) General:I. Balance of capacity 10 kg, and sensitivity of 1 gm.

II. Balance of capacity 200 gms and sensitivity of 0.01 gm.III. Drying oven.IV. Desiccators.V. Containers for water content.VI. Graduated Jar.

VII. Trimming knife.VIII. Large mixing tray.




THEORY:Compaction is the process of densification of soil mass by reducing air voids. The purpose of laboratory compaction test is so determine the proper amount of water at which the weight of the soil grains in a unit volume of the compacted is maximum, the amount of water is thus called the Optimum Moisture Content (OMC). In the laboratory different values of moisture contents and the resulting dry densities, obtained after compaction are plotted both to arithmetic scale, the former as abscissa and the latter as ordinate. The points thus obtained are joined together as a curve. The maximum dry density and the corresponding OMC are read from the curve.

For example




The standard equipment shown below,




The wet density of the compacted soil is calculated as below,

Where, w1 = Weight of mould with moist compacted soil.w2 = Weight of empty mould.V = Volume of mould.

The dry density of the soil shall be calculated as follows,

Where, t = wet density of the compacted soil.w = moisture content

APPLICATION:Soil Mechanics Lab Manual - 7 -

- 7 -Prepared By Nirali B. Hasilkar & Bhavita S. DaveAssist. Prof., PIT, Limda.


Compaction of soil increases the density, shear strength, bearing capacity, thus reducing the voids, settlement and permeability. The results of this are useful in the stability of field problems like earthen dams, embankments, roads and airfield. In such compacted in the field is controlled by the value of the OMC determined by laboratory compaction test. The compaction energy to be given by a compaction unit is also controlled by the maximum dry density determined in the laboratory. In other words, the laboratory compaction tests results are used to write the compaction specification for field compaction of the soil.

PROCEDURE:

I. Take about 20 kg of soil and sieve it through 20 mm and 4.75 mm.II. A 100 mm diameter Proctor mould is to be used if the soil fraction that passes 4.75

mm sieve is greater than 80% by weight.III. Take about 2.25 kg of the soil sample and add water to get the moisture content

round 8%. Leave the mix to mature for few minutes.IV. Clean and grease gently the inside surface of the mould, and the base plate.V. Take the weight of empty mould with the base plate.VI. Fir the collar and place the mould on a solid base.

VII. Place first batch of soil inside the mould and apply 25 blows of Standard rammer, so that the compacted layer thickness is about one-third height of the mould Scratch the top of the compacted soil before the second layer is placed Place the second batch of wet soil and follow the same procedure In all the soil is compacted in three layers, each given 25 blows of the standard rammer weighing 2.6 Kg and having a drop of 310 mm.

VIII. Remove the collar, and trim of the excess soil with trimming knife. Clean the mould, and weight the mould with the compacted soil and the base plate.

IX. Take a representative sample from the mould and determine its water content.X. Repeat the above procedure for water content values of 13%, 17%, 20%, 22% and

25%.

PRECAUTIONS:

I. Adequate period is allowed to mature the soil after it is mixed with water.II. The rammer blows should be uniformly distributed over the surface with spatula

before next layer is placed. III. To avoid stratification each compacted layer should be scratched with spatula

before next layer is placed.




IV. At the end of compaction test, the soil should not penetrate more than 5mm into the collar.

OBSERVATION AND CALCULATION TABLE:

I. Diameter of mould, D (cm): __ _ _ _ _ _ _II. Height of mould, h (cm) : _ _ _ _ _ _ _ _III. Volume of mould, V (cc) : _ _ _ _ _ _ _ _

Weight of empty mould + Base plate (w1) ,kg

Weight of compacted soil + Base plate (w2) ,kgBulk unit weight of compacted soil γ (gm/cc)Water content (w)

Dry unit weight γd = γ / (1 + w), (gm/cc)




EXPERIMENT: 2

CALIFORNIA BEARING RATIO TEST

CALIFORNIA BEARING RATIO TEST

OBJECTIVESoil Mechanics Lab Manual - 10 -



To determine the California bearing ratio by conducting a load penetration test in the laboratory.

NEED AND SCOPE The california bearing ratio test is penetration test meant for the evaluation of

subgrade strength of roads and pavements. The results obtained by these tests are used with the empirical curves to determine the thickness of pavement and its component layers. This is the most widely used method for the design of flexible pavement.

This instruction sheet covers the laboratory method for the determination of C.B.R. of undisturbed and remoulded /compacted soil specimens, both in soaked as well as unsoaked state.

APPARATUS REQUIRED:

1. Cylindrical mould with inside dia 150 mm and height 175 mm, provided with a detachable extension collar 50 mm height and a detachable perforated base plate 10 mm thick.

2. Spacer disc 148 mm in dia and 47.7 mm in height along with handle. 3. Metal rammers. Weight 2.6 kg with a drop of 310 mm (or) weight 4.89 kg a drop

450 mm. 4. Weights. One annular metal weight and several slotted weights weighing 2.5 kg

each, 147 mm in dia, with a central hole 53 mm in diameter. 5. Loading machine. With a capacity of atleast 5000 kg and equipped with a

movable head or base that travels at an uniform rate of 1.25 mm/min. Complete with load indicating device.

6. Metal penetration piston 50 mm dia and minimum of 100 mm in length. 7. Two dial gauges reading to 0.01 mm. 8. Sieves. 4.75 mm and 20 mm I.S. Sieves.9. Miscellaneous apparatus, such as a mixing bowl, straight edge, scales soaking

tank or pan, drying oven, filter paper and containers.

THEORY:

DEFINITION OF C.B.R.Soil Mechanics Lab Manual - 11 -



It is the ratio of force per unit area required to penetrate a soil mass with standard circular piston at the rate of 1.25 mm/min. to that required for the corresponding penetration of a standard material.

C.B.R. = Test load/Standard load � 100

The following table gives the standard loads adopted for different penetrations for the standard material with a C.B.R. value of 100%

Penetration of plunger (mm) Standard load (kg)2.55.07.510.012.5

13702055263031803600

The test may be performed on undisturbed specimens and on remoulded specimens which may be compacted either statically or dynamically.

PREPARATION OF TEST SPECIMEN Undisturbed specimen

Attach the cutting edge to the mould and push it gently into the ground. Remove the soil from the outside of the mould which is pushed in. When the mould is full of soil, remove it from weighing the soil with the mould or by any field method near the spot.

Determine the density Remoulded specimen

Prepare the remoulded specimen at Proctors maximum dry density or any other density at which C.B.R. is required. Maintain the specimen at optimum moisture content or the field moisture as required. The material used should pass 20 mm I.S. sieve but it should be retained on 4.75 mm I.S. sieve. Prepare the specimen either by dynamic compaction or by static compaction.

Dynamic Compaction




1. Take about 4.5 to 5.5 kg of soil and mix thoroughly with the required water.

2. Fix the extension collar and the base plate to the mould. Insert the spacer disc over the base. Place the filter paper on the top of the spacer disc.

3. Compact the mix soil in the mould using either light compaction or heavy compaction. For light compaction, compact the soil in 3 equal layers, each layer being given 55 blows by the 2.6 kg rammer. For heavy compaction compact the soil in 5 layers, 56 blows to each layer by the 4.89 kg rammer.

4. Remove the collar and trim off soil.5. Turn the mould upside down and remove the base plate and the

displacer disc.6. Weigh the mould with compacted soil and determine the bulk density

and dry density.7. Put filter paper on the top of the compacted soil (collar side) and clamp

the perforated base plate on to it.

Static compaction

Calculate the weight of the wet soil at the required water content to give the desired density when occupying the standard specimen volume in the mould from the expression. W =desired dry density * (1+w) V

Where. W = Weight of the wet soilw = desired water content

V = volume of the specimen in the mould = 2250 cm3 (as per the mould available in laboratory)

1. Take the weight W (calculated as above) of the mix soil and place it in the mould.

2. Place a filter paper and the displacer disc on the top of soil.3. Keep the mould assembly in static loading frame and compact by pressing

the displacer disc till the level of disc reaches the top of the mould.4. Keep the load for some time and then release the load. Remove the

displacer disc.5. The test may be conducted for both soaked as well as unsoaked conditions.6. If the sample is to be soaked, in both cases of compaction, put a filter paper

on the top of the soil and place the adjustable stem and perforated plate on the top of filter paper.




7. Put annular weights to produce a surcharge equal to weight of base material and pavement expected in actual construction. Each 2.5 kg weight is equivalent to 7 cm construction. A minimum of two weights should be put.

8. Immerse the mould assembly and weights in a tank of water and soak it for 96 hours. Remove the mould from tank.

9. Note the consolidation of the specimen.

Procedure for Penetration Test

1. Place the mould assembly with the surcharge weights on the penetration test machine.

2. Seat the penetration piston at the center of the specimen with the smallest possible load, but in no case in excess of 4 kg so that full contact of the piston on the sample is established.

3. Set the stress and strain dial gauge to read zero. Apply the load on the piston so that the penetration rate is about 1.25 mm/min.

4. Record the load readings at penetrations of 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 4.0, 5.0, 7.5, 10 and 12.5 mm. Note the maximum load and corresponding penetration if it occurs for a penetration less than 12.5 mm.

5. Detach the mould from the loading equipment. Take about 20 to 50 g of soil from the top 3 cm layer and determine the moisture content.

Observation and Recording




For Dynamic Compaction

Optimum water content (%) Weight of mould + compacted specimen g Weight of empty mould g Weight of compacted specimen g Volume of specimen cm3 Bulk density g/cc Dry density g/cc

For static compactionDry density g/ccMoulding water content %Wet weight of the compacted soil, (W)gPeriod of soaking 96 hrs. (4days).

For penetration TestCalibration factor of the proving ring 1 Div. = 1.176 kgSurcharge weight used (kg) 2.0 kg per 6 cm constructionWater content after penetration test %Least count of penetration dial 1 Div. = 0.01 mm

If the initial portion of the curve is concave upwards, apply correction by drawing a tangent to the curve at the point of greatest slope and shift the origin (Fig. 40). Find and record the correct load reading corresponding to each penetration.

C.B.R. = PT /PS * 100

Where, PT = Corrected test load corresponding to the chosen penetration from the load penetration curve.

PS = Standard load for the same penetration taken from the table I.




Penetration Dial Load Dial Corrected Load

Readings Penetration (mm)

proving ring reading Load (kg)

Interpretation and recording

C.B.R. of specimen at 2.5 mm penetration C.B.R. of specimen at 5.0 mm penetration C.B.R. of specimen at 2.5 mm penetration

The C.B.R. values are usually calculated for penetration of 2.5 mm and 5 mm. Generally the C.B.R. value at 2.5 mm will be greater that at 5 mm and in such a case/the former shall be taken as C.B.R. for design purpose. If C.B.R. for 5 mm exceeds that for 2.5 mm, the test should be repeated. If identical results follow, the C.B.R. corresponding to 5 mm penetration should be taken for design.




EXPERIMENT: 3

CONSOLIDATION / OEDOMETER TEST




CONSOLIDATION TESTDATE:


To determine the settlements due to primary consolidation of soil by conducting one dimensional test to determine:

I. Rate of consolidation under normal load.II. Degree of consolidation at any time.III. Pressure-void ratio relationship.IV. Coefficient of consolidation at various pressures.V. Compression index.

APPARATUS REQUIRED:1) Consolidometer consisting essentially;

a) A ring of diameter = 60mm and height = 20mmb) Two porous plates or stones of silicon carbide, aluminium oxide or porous metal.c) Guide ring.d) Outer ring.e) Water jacket with base.f) Pressure pad.g) Rubber basket.

2) Loading device consisting of frame, lever system, loading yoke dial gauge fixing device and weights.

3) Dial gauge to read to an accuracy of 0.002mm.4) Thermostatically controlled oven.5) Stopwatch to read seconds.6) Sample extractor.7) Miscellaneous items like balance, soil trimming tools, spatula, filter papers, sample

containers.

THEORY:




When a compressive load is applied to soil mass, a decrease in its volume takes place, the decrease in volume of soil mass under stress is known as compression and the property of soil mass pertaining to its tendency to decrease in volume under pressure is known as compressibility. In a saturated soil mass having its void filled with incompressible water, decrease in volume or compression can take place when water is expelled out of the voids. Such a compression resulting from a long time static load and the consequent escape of pore water is termed as consolidation.Then the load is applied on the saturated soil mass, the entire load is carried by pore water in the beginning. As the water starts escaping from the voids, the hydrostatic pressure in water gets gradually dissipated and the load is shifted to the soil solids which increases effective on them, as a result the soil mass decrease in volume. The rate of escape of water depends on the permeability of the soil.

Major problem in the soil is the soil subsidence caused by pressure or weight of construction trucks on the surface, which may be divided into three categories.

1. Elastic Deformation2. Primary Consolidation3. Secondary Consolidation

The equipment arrangement is as fallows;




APPLICATION:The test is conducted to determine the settlement due to primary consolidation. To determine:1) Rate of consolidation under normal load.2) Degree of consolidation at any time.3) Pressure-void ratio relationship.4) Coefficient of consolidation at various pressures.5) Compression index.

From the above information it will be possible for us to predict the time rate and extent of settlement of structures founded on fine-grained soils. It is also helpful in analyzing the stress history of soil. Since the settlement analysis of the foundation depends mainly on the values determined by the test, this test is very important for foundation design.

PROCEDURE:

1) Preparation of the soil specimen:

A) From undisturbed soil sample:From the sample tube, eject the sample into the consolidation ring. The sample

should project about one cm from outer ring. Trim the sample smooth and flush with top and bottom of the ring by using a knife. Clean the ring from outside and keep it ready from weighing.




B) From remoulded or disturb sample :Choose the density and water content at which sample has to be compacted from

the moisture density relationship. Calculate the quantity of soil and water required to mix and compact. Compact the specimen in compaction mould in three layers usingthe standard rammers. Eject the specimen from the mould using the sample extractor.

2) Saturate two porous stones either by boiling in distilled water about 15 minute or by keeping them submerged in the distilled water for 4 to 8 hrs. Wipe away excess water. Fittings of the consolidometer which is to be enclosed shall be moistened.

3) Assemble the consolidometer, with the soil specimen and porous stones at top and bottom of specimen, providing a filter paper between the soil specimen and porous stone. Position the pressure pad centrally on the top porous stone.

4) Mount the mould assembly on the loading frame, and center it such that the load applied is axial.

5) Position the dial gauge to measure the vertical compression of the specimen. The dial gauge holder should be set so that the dial gauge is in the begging of its releases run, allowing sufficient margin for the swelling of the soil, if any.

6) Connect the mould assembly to the water reservoir and the sample is allowed to saturate. The level of the water in the reservoir should be at about the same level as the soil specimen.

7) Apply an initial load to the assembly. The magnitude of this load should be chosen by trial, such that there is no swelling. It should be not less than 50 g/cm 2 (5 kN/m2) for ordinary soils & 25 g/cm2 (2.5 kN/m2) for very soft soils. The load should be allowed to stand until there is no change in dial gauge readings for two consecutive hours or for a maximum of 24 hours.

8) Note the final dial reading under the initial load. Apply first load of intensity 0.1 kg/cm 2

(10 kN/m2) start the stop watch simultaneously. Record the dial gauge readings at various time intervals (and fill in the table). The dial gauge readings are taken until 90% consolidation is reached. Primary consolidation is gradually reached within 24 hrs.

9) At the end of the period, specified above take the dial reading and time reading. Double the load intensity and take the dial readings at various time intervals. Repeat this procedure fir successive load increments.




10)The usual loading intensity are as follows: 0.1, 0.2, 0.5, 1, 2, 4 and 8 kg/cm2

11)After the last loading is completed, reduce the load to half (1/2) of the value of the last load and allow it to stand for 24 hrs. Reduce the load further in steps of 1/4 th the previous intensity till an intensity of 0.1 kg/cm2 is reached. Take the final reading of the dial gauge.

12) Reduce the load to the initial load, keep it for 24 hrs and note the final readings of the dial gauge.

13)Quickly dismantle the specimen assembly and remove the excess water on the soil specimen in oven, note the dry weight of it.

PRECAUTIONS:

1) While preparing the specimen, attempts has to be made to have the soil strata orientated in the same direction in the consolidation apparatus.

2) During trimming care should be taken in handling the soil specimen with least pressure.

3) Smaller increments of sequential loading have to be adopted for soft soils.

OBSERVATION AND CALCULATION TABLE:

Empty weight of ring: Area of ringDiameter of ring Volume of ringDial gauge Specific Gravity of soilHeight of ring

PRESSURE INTENSITY

(KN/ m2)

10 20 50 100 200

Elapsed time

(min)

___

√ t DIAL GAUGE READINGS(10—2 mm)

0 0Soil Mechanics Lab Manual - 22 -



0.25 0.51 12.25 1.54 26.25 2.59 316 425 536 649 764 824 HRS.

OBSERVATION SHEET FOR CONSOLIDATION TEST: WATER CONTENTS:

BEFORE TEST AFTER TEST

MASS OF RING + WET

SOIL

MASS OF RING + DRY

SOIL

MASS OF RING

MASS OF DRY SOIL

(Md)




MASS OF WATER

WATER CONTENT (w)

Degree of Saturation (S)

Height of Solids Hs = Md/GAρw

OBSERVATION SHEET FOR CALCULATION OF VOIDS RATIO

BY HEIGHT OF SOLIDS METHODINITIAL HEIGHT OF SPECIMEN (H0) S. GRAVITY (G)

C/S AREA OF SPECIMEN (A) WATER CONTENT (w)

VOLUME OF CYLINDER (V) DRY MASS (Md)

Applied

Pressure

σ (KN/m2)

FINAL

DIAL

READING

DIAL

CHANGE

∆ H (mm)

SECIMEN

HEIGHT(H)

= H1+ ∆ H

HEIGHT

OF VOIDS

H -- Hs

VOIDS

RATIO

e = H—Hs

Hs

REMARKS




CALCULATION OF VOIDS RATIO BY CHANGE IN VOIDS RATIO METHOD:INITIAL HEIGHT OF SPECIMEN (H0) S. GRAVITY (G)

C/S AREA OF SPECIMEN (A) WATER CONTENT (wf)

VOLUME OF CYLINDER (V) FINAL HT. OF SECIMEN (Hf)

FINAL VOIDS RATIO (ef) = Wg ∆e = H + ef X ∆ H

Hf

Applied

pressure

Final dial

reading

Change in

thickness

∆ H(mm)

Specimen

height H =

H1+ ∆ H

Change in

voids ratio

∆e

Voids ratio

e

CALCULATIONS:

1. Heights of solids (Hs) is calculated from the equation Hs = Md / G x A x ρw

2. Voids ratio is calculated from the equatione = H—Hs

Hs3. Co-efficient of consolidation The Coefficient of consolidation at each

pressures increment is calculated by using the following equations: It is




determined by the following 2 methods (a) square root of time fitting method

Cv = 0.848 d2/t9o (b) Logarithm of time fitting method.

Cv = 0.197 d2/t50 (Log fitting method) In the log fitting method a plot is made between dial readings and logarithmic of

time. The time corresponding to 50% consolidation is determined. In the square root fitting method a plot is made between dia1 readings and square

root of time and the time corresponding to 90% consolidation is determined. The values of CV are recorded in table 1I

4. Compression index to determine the compression index, a plot of voids ratio (e) Vs log t is made'. The initial compression curve would be a straight line and the slope of this line would give the compression index CC.

5. Co-efficient of compressibility is calculated as followsav = 0.435 CC .

Average pressure for the increment6. Co-efficient of permeability is calculated as follows

K = CV aV γW

(1+e)

Graphs

(1) Dial gauge Vs log of time or dial reading Vs square root of time(2) Voids ratio Vs log σ(avg. pressure for the increment)







EXPERIMENT NO: 4

DIRECT SHEAR TEST

DIRECT SHEAR TESTDATE:


To determine the shearing strength of the soil using the direct shear apparatus.

APPARATUS:Soil Mechanics Lab Manual - 28 -



1. Direct shear box apparatus2. Loading frame (motor attached)3. Dial gauge4. Proving ring5. Tamper6. Straight edge7. Balance to weigh upto 200 mg8. Aluminum container

KNOWLEDGE OF EQUIPMENT:Strain controlled direct shear machine consists of shear box, soil container, loading unit, proving ring, dial gauge to measure shear deformation and volume changes. A two piece square shear box is one type of soil container used. A proving ring is used to indicate the shear load taken by the soil initiated in the shearing plane..

THEORY:

Shear strength of a soil is the maximum resistance to shearing stress at failure on the failure plane.

Shear strength is composed of:

1) Internal friction which is the resistance due to friction between individual particles at their contact points and interlocking of particles. This interlocking strength is indicated through parameter φ.

2) Cohesion which resistance due to inter-particle force which tend hold the particles together in a soil mass. The indicative parameter is called Cohesion intercept (c).

Coulomb has represented the shear strength of soil by the equation:




Where, Ʈf = shear strength of soil = shear stress at failure.C = Cohesion intercepts.σn = Total normal stress on the failure planeφ = Angle of internal friction or shearing resistance

The graphical representation of the above equation gives a straight line called Failure envelope.

The parameters c and are not constant for a given type of soil but depends in its degree of saturation, drainage conditions and the condition of laboratory testing.

In direct shear test, the sample is sheared along the horizontal plane. This indicates that the failure plane is horizontal. The normal stress, on this plane is the external vertical load divided by the corrected area of the soil sample. The shear stress at failure is the external lateral load divided by the corrected of soil sample.

APPLICATION:

The purpose of direct shear test is to get the ultimate shear resistance, peak shear resistance, cohesion, angle of shearing resistance and stress-strain characteristics of the soils.

Shear parameters are used in the design of earthen dams and embankments. These are used in calculating the bearing capacity of soil-foundation systems. These parameter help in estimating the earth pressures behind the retaining walls. The values of these parameters are also used in checking the stability to natural slopes, cuts and fills.

PROCEDURE

Check the inner dimension of the soil container.




Put the parts of the soil I container together. Calculate the volume of the container. Weigh the container. Place the soil in smooth layers (approximately 10 mm thick). If a dense sample is

desired tamp the soil. Weighsoil container, the difference of these two is the weight of the soil. Calculate

the density of the soil. Make the surface of the soil plane. Put the upper grating on stone and loading block on top of the soil. Measure the thickness of soil specimen. Apply the desired normal load. Remove the shear pin. Attach the dial gauge which measures the change of volume. Record the initial reading of the dial gauge and calibration values. Before proceeding to the test check all the adjustments to see that there is no

connection between two parts except sand/ soils. Start the motor. Take the reading of the shear force and record the

reading. Take volume change readings till failure. Add 5 kg normal stress 0.5 kg/cm2 and continue the experiment till failure Record carefully all the readings. Set the dial gauges zero, before starting the

experiment.

PRECAUTIONS:

Before starting the test, the upper half of the box should be brought in proper contact with the proving ring.

Before subjecting the specimen to shear, the fixing screws should take out.

Spacing screws should also be removed before shearing the specimen.

No vibrations should be transmitted to the specimen during the test. Do not forget to add the self weight of the loading yoke in the vertical

loads.Soil Mechanics Lab Manual - 31 -



DATA CALCULATION SHEET FOR DIRECT SHEAR TEST:Normal stress 0.5 Kg/cm2 L.C. = __________ P.R.C = __________

Horizonta

l gauge

reading

Vertical

dial

gauge

reading

Proving

ring

reading

Hori.

Dial

gauge

reading

Shear

deformation

col.(4) x

least count

Vertical

gauge

reading

initial

Vertical

deformation

= div. in

col.6x L.C

Proving

reading

initial

reading

Shear stress=

div.

col(8)xproving

ring constant Soil Mechanics Lab Manual - 32 -



Initial

reading

div.

gauge

of dial reading of dial

gauge

area of the

specimen

Kg/cm2

1 2 3 4 5 6 7 8 9

0

25

50

75

100

125

150

175

200

250

300

400

500

600

700

800

900


Horizonta

l gauge

reading

Vertical

dial

gauge

Proving

ring

reading

Hori.

Dial

gauge

Shear

deformation

col.(4) x

Vertical

gauge

reading

Vertical

deformation

= div. in

Proving

reading

initial

Shear stress=

div.

col(8)xproving




reading reading

Initial

reading

div.

gauge

least count

of dial

initial

reading

col.6x L.C

of dial

gauge

reading ring constant

area of the

specimen

Kg/cm2

1 2 3 4 5 6 7 8 9

0

25

50

75

100

125

150

175

200

250

300

400

500

600

700

800

900

DATA CALCULATION SHEET FOR DIRECT SHEAR TEST:Normal stress 1.5Kg/cm2 L.C. = __________ P.R.C = __________

Horizonta

l gauge

Vertical

dial

Proving

ring

Hori.

Dial

Shear

deformation

Vertical

gauge

Vertical

deformation

Proving

reading

Shear stress=

div.




reading gauge

reading

reading gauge

reading

Initial

reading

div.

gauge

col.(4) x

least count

of dial

reading

initial

reading

= div. in

col.6x L.C

of dial

gauge

initial

reading

col(8)xproving

ring constant

area of the

specimen

Kg/cm2

1 2 3 4 5 6 7 8 9

0

25

50

75

100

125

150

175

200

250

300

400

500

600

700

800

900


Horizonta Vertical Proving Hori. Shear Vertical Vertical Proving Shear stress=




l gauge

reading

dial

gauge

reading

ring

reading

Dial

gauge

reading

Initial

reading

div.

gauge

deformation

col.(4) x

least count

of dial

gauge

reading

initial

reading

deformation

= div. in

col.6x L.C

of dial

gauge

reading

initial

reading

div.

col(8)xproving

ring constant

area of the

specimen

Kg/cm2

1 2 3 4 5 6 7 8 9

0

25

50

75

100

125

150

175

200

250

300

400

500

600

700

800

900

OBSERVATION AND RECORDINGS




Proving ring constant least count of dial-----------

Calibration factor

Leverage factor

Dimensions of shear box 60 x 60 mm

Empty weight of shear box

Least count of dial gauge

Volume change

Sr.no Normal load

kg

Normal stress =

load x leverage

area

kg/cm2

Shear stress = Proving ring reading x calibration

Area of container

kg/cm2

1

2

3

GENERAL REMARKS 1. In the shear box test,-the specimen is not failing along its weakest plane but along

a predetermined or induced failure plane i.e. horizontal plane separating the two halves of the shear box. This is the main draw back of this test. Moreover, during loading, the state of stress cannot be evaluated. It can be evaluated only at failure condition i.e. Mohr's circle can be drawn at the failure condition only. Also failure is progressive.

2. Direct shear test is simple and faster to operate. As thinner specimens are used in shear box, they facilitate drainage of pore water from a saturated sample in less




time. This test is also useful to study friction between two materials - one material in lower half of box and another material in the upper half of box.

3. The angle of' shearing resistance of sands depends on state of compaction, coarseness of grains, particle shape and roughness of grain surface and grading. It varies between 28"(uniformly graded sands with round grains in very loose state) to 46° (well graded sand with angular grain~ in dense state).

4. The volume change in sandy soil is a complex phenomenon depending on gradation, article shape, state and type of packing, orientation of principal planes, principal stress ratio. Stress history, magnitude of minor principal stress, type of apparatus, test procedure, method of preparing specimen etc. In general Loose sands expand and dense sands contract in volume on shearing There is a void ratio at which either expansion contraction in volume takes place. This void ratio is called critical void ratio. Expansion or contraction can be inferred from the movement of vertical dial gauge during shearing.

5. The friction between sand particles is due to sliding and rolling friction and interlocking action.

6. The ultimate values of soil parameter for both loose sand and dense sand approximately attain the same value so, if angle of friction value is calculated at ultimate stage, slight disturbance in density during sampling and preparation of test specimen will not have much effect.




EXPERIMENT NO: 5

INCONFINED COMPRESSION TEST




INCONFINED COMPRESSION TEST

OBJECTIVE

To determine shear parameters of cohesive soil

NEED AND SCOPE OF THE EXPERIMENT

It is not always possible to conduct the bearing capacity test in the field. Some times it is cheaper to take the undisturbed soil sample and test its strength in the laboratory. Also to choose the best material for the embankment, one has to conduct strength tests on the samples selected. Under these conditions it is easy to perform the unconfined compression test on undisturbed and remoulded soil sample. Now we will investigate experimentally the strength of a given soil sample. APPARATUS REQUIRED:

1. Loading frame of capacity of 2 t, with constant rate of movement. What is the least count of the dial gauge attached to the proving ring!

2. Proving ring of 0.01 kg sensitivity for soft soils; 0.05 kg for stiff soils.3. Soil trimmer.4. Frictionless end plates of 75 mm diameter (Perspex plate with silicon

grease coating).5. Evaporating dish (Aluminum container).6. Soil sample of 75 mm length.7. Dial gauge (0.01 mm accuracy).8. Balance of capacity 200 g and sensitivity to weigh 0.01 g.9. Oven, thermostatically controlled with interior of non-corroding material

to maintain the temperature at the desired level. What is the range of the temperature used for drying the soil !

10.Sample extractor and split sampler.11.Dial gauge (sensitivity 0.01mm).12.Vernier calipers

PROCEDURE (SPECIMEN) In this test, a cylinder of soil without lateral support is tested to failure in

simple compression, at a constant rate of strain. The compressive load per unit area required to fail the specimen as called Unconfined compressive strength of the soil.Soil Mechanics Lab Manual - 40 -



Preparation of specimen for testing

A. Undisturbed specimen:

1. Note down the sample number, bore hole number and the depth at which the sample was taken.

2. Remove the protective cover (paraffin wax) from the sampling tube.3. Place the sampling tube extractor and push the plunger till a small

length of sample moves out.4. Trim the projected sample using a wire saw.5. Again push the plunger of the extractor till a 75 mm long sample

comes out.6. Cutout this sample carefully and hold it on the split sampler so that

it does not fall.7. Take about 10 to 15 g of soil from the tube for water content

determination.8. Note the container number and take the net weight of the sample

and the container.9. Measure the diameter at the top, middle, and the bottom of the

sample and find the average and record the same.10.Measure the length of the sample and record.11.Find the weight of the sample and record.

B. Moulded sample

1. For the desired water content and the dry density, calculate the weight of the dry soil Ws required for preparing a specimen of 3.8 cm diameter and 7.5 cm long.

2. Add required quantity of water Ww to this soil. Ww = WS � W/100 gm3. Mix the soil thoroughly with water.4. Place the wet soil in a tight thick polythene bag in a humidity chamber and

place the soil in a constant volume mould, having an internal height of 7.5 cm and internal diameter of 3.8 cm.

5. After 24 hours take the soil from the humidity chamber and place the soil in a constant volume mould, having an internal height of 7.5 cm and internal diameter of 3.8 cm.

6. Place the lubricated moulded with plungers in position in the load frame.




7. Apply the compressive load till the specimen is compacted to a height of 7.5 cm.

8. Eject the specimen from the constant volume mould.9. Record the correct height, weight and diameter of the specimen.

Test procedure

1. Take two frictionless bearing plates of 75 mm diameter.2. Place the specimen on the base plate of the load frame (sandwiched

between the end plates).3. Place a hardened steel ball on the bearing plate.4. Adjust the center line of the specimen such that the proving ring and the

steel ball are in the same line.5. Fix a dial gauge to measure the vertical compression of the specimen.6. Adjust the gear position on the load frame to give suitable vertical

displacement.7. Start applying the load and record the readings of the proving ring dial and

compression dial for every 5 mm compression.8. Continue loading till failure is complete.9. Draw the sketch of the failure pattern in the specimen.

Project : Tested by : Location : Boring No. : Depth :

Sample detailsType UD/R : soil descriptionSpecific gravity (GS) 2.71 Bulk densityWater content Degree of saturation .%Diameter (Do) of the sample cm Area of cross-section = cm2Initial length (Lo) of the sample = 76 mm

Elapsed time

(minutes)

1

Compression dial reading (L) (mm)

2

Straine =

L * 100/Lo (%)

3

Area AAo /(1-e)

(cm)2

4

Proving ring

reading (Divns.)

5

Axial load (kg)

6

Compressive stress

(kg/cm2)

7




Interpretation and Reporting

Unconfined compression strength of the soil = qu =

Shear strength of the soil = qu/2 =

Sensitivity = (qu for undisturbed sample)/ (qu for remoulded sample).

GENERAL REMARKS

Minimum three samples should be tested, correlation can be made between unconfined strength and field SPT value N. Up to 6% strain the readings may be taken at every min (30 sec).�




EXPERIMENT NO: 6

DEMONSTRATION OF TRIAXIAL TEST




DEMONSTRATION OF TRIAXIAL TEST


To find the shear of the soil by Undrained Triaxial Test.

APPARATUS REQUIRED:1) Special:

i) A constant rate of strain compression machine of which the following is a brief description of one is in common use.A) A loading frame in which the load is applied by yoke acting through

an elastic dynamometer, more commonly called a proving ring which used to measure the load. The frame is operated at a constant rate by a geared screw jack. It is preferable for the machine to be motor driven, by a small electric motor.

B) A hydraulic pressure apparatus including an air compressor and water reservoir in which air under pressure acting on the water raises it to the required pressure, together with the necessary control valves and pressure dials.

ii) A triaxial cell to take 3.8 cm dia and 7.6 cm long samples, in which the sample can be subjected to an all round hydrostatic pressure, together with a vertical compression load acting through a piston. The vertical load from the piston acts on a pressure cap. The cell is usually




designed with a non-ferrous metal top and base connected by tension rods and with walls formed of Perspex.

2) General:I) 3.8 cm (1.5 inch) internal diameter 12.5 cm (5 inches) long sample tubes.II) Rubber ring.III) An open ended cylindrical section former, 3.8 cm inside dia, fitted with a small rubber tube in its side.IV) Stop clock.V) Moisture content test apparatus.VI) A balance of 250 gm capacity and accurate to 0.01 gm.THEORY:

Triaxial test is more reliable because we can measure both drained and untrained shear strength. Generally 1.4” diameter (3” tall) or 2.8” diameter (6” tall) specimen is used. Specimen is encased by a thin rubber membrane and set into a plastic cylindrical chamber. Cell pressure is applied in the chamber (which represents σ3’) by pressurizing the cell fluid (generally water).




Vertical stress is increased by loading the specimen (by raising the platen in strain controlled test and by adding loads directly in stress controlled test, but strain controlled test is more common) until shear failure occurs. Total vertical stress, which is σ1’ is equal to the sum of σ3’ and deviator stress (σd). Measurement of σd, axial deformation, pore pressure, and sample volume change are recorded.

Depending on the nature of loading and drainage condition, triaxial tests are conducted in three different ways.i. UU Triaxial test




ii. CU Triaxial testiii. CD Triaxial test

APPLICATION:UU triaxial test gives shear strength of soil at different confining stresses. Shear strength is important in all types of geotechnical designs and analyses.

PROCEDURE:I) The sample is placed in the compression machine and a pressure

plate is placed on the top. Care must be taken to prevent any part of the machine or cell from jogging the sample while it is being setup, for example, by knocking against this bottom of the loading piston. The probable strength of the sample is estimated and a suitable proving ring selected and fitted to the machine.

II) The cell must be properly set up and uniformly clamped down to prevent leakage of pressure during the test, making sure first that the sample is properly sealed with its end caps and rings (rubber) in position and that the sealing rings for the cell are also correctly placed.

III) When the sample is setup water is admitted and the cell is fitted under water escapes from the beed valve, at the top, which is closed. If the sample is to be tested at zero lateral pressure water is not required.

IV) The air pressure in the reservoir is then increased to raise the hydrostatic pressure in the required amount. The pressure gauge must be watched during the test and any necessary adjustments must be made to keep the pressure constant.

V) The handle wheel of the screw jack is rotated until the underside of the hemispherical seating of the proving ring, through which the loading is applied, just touches the cell piston.

VI) The piston is then removed down by handle until it is just in touch with the pressure plate on the top of the sample, and the proving ring seating is again brought into contact for the begging of the test.




PRECAUTIONS:OBSERVATION AND CALCULATION TABLE:The machine is set in motion (or if hand operated the hand wheel is turned at a constant rate) to give a rate of strain 2% per minute. The strain dial gauge reading is then taken and the corresponding proving ring reading is taken the corresponding proving ring chart. The load applied is known. The experiment is stopped at the strain dial gauge reading for 15% length of the sample or 15% strain.i. Size of specimen :ii. Length :iii. Proving ring constant :iv. Diameter : 3.81 cmv. Initial area L:vi. Initial Volume :vii. Strain dial least count (const) :







GENERAL REMARKS:

I) It is assumed that the volume of the sample remains constant and that the area of the sample increases uniformly as the length decreases. The calculation of the stress is based on this new area at failure, by direct calculation, using the proving ring constant and the new area of the sample. By constructing a chart relating strains readings, from the proving ring, directly to the corresponding stress.

II) The strain and corresponding stress is plotted with stress abscissa and curve is drawn. The maximum compressive stress at failure and the corresponding strain and cell pressure are found out.

III) The stress results of the series of triaxial tests at increasing cell pressure are plotted on a mohr stress diagram. In this diagram a semicircle is plotted with normal stress as abscissa shear stress as ordinate.

IV) The condition of the failure of the sample is generally approximated to by a straight line drawn as a tangent to the circles, the equation of which is t = C + a tan f. The value of cohesion ‘C’ is read of the shear stress axis, where it is cut by the tangent to the mohr circles, and the angle of shearing resistance (f) is angle between the tangent and a line parallel to the shear stress.




EXPERIMENT NO: 7

AUGER BORING / SAMPLING




AUGER BORING / SAMPLING

Site investigations or subsurface explorations are done for obtaining the

information about subsurface conditions at the site of proposed construction. It

consists of determining the profile of the natural soil deposits at the site, taking

the soil samples and determining the engineering properties of the soils. It also

includes in-situ testing of the soils. Site investigations are generally done to

obtain the information that is useful for one or more of the following purposes:

1. To select the type and depth of foundation for a given structure

2. To determine the bearing capacity of the soil.

3. To estimate the probable maximum and differential settlements

4. To establish the ground water level and to determine the properties of

water

5. To predict the lateral earth pressure against retaining walls and

abutments

6. To predict and solve potential foundation problems

7. To ascertain the suitability of the soil as a construction material

8. To investigate the safety of the existing structure and to suggest the

remedial measures




The relevant information is available by drilling holes, taking the soil samples and

determining the index and engineering properties of the soil. In-situ tests are

conducted to determine the properties of the soil in natural conditions.

STAGES IN SUB-SURFACE INVESTIGATIONS:

Sub surface explorations are generally carried out in three stages:Reconnaissance: site reconnaissance is the first step in a sub surface

exploration programme. It includes a visit to the site and to study the maps and

other relevant records. It helps in deciding future programme of site

investigations, scope of work, methods of exploration to be adopted, types of

samples to be taken and the laboratory testing and in-situ testing.

1) Preliminary Explorations: To determine the depth, thickness,

extent and composition of each soil stratum at site preliminary

explorations are done. It is in the form of borings or test pits. Tests are

conducted with cone penetrometers.

2) Detailed explorations: the purpose of detailed explorations is to

determine the engineering properties of soils in different strata. It

includes extensive boring programme, sampling and testing of the

sample in the laboratory.

BORINGS FOR EXPLORATION: When the depth of exploration is large, borings are used for exploration. A

vertical bore hole is drilled in the ground to get the information about the




sub-soil strata. Samples are taken from the bore hole and tested in a

laboratory. The bore hole may be used for conducting in-situ tests and for

locating the water table.

Depending upon the type of soil and the purpose of boring , following

methods are used for drilling holes.

AUGER BORING

An auger is a boring tool similar to one used by a carpenter for boring

holes in wood.

It consists of a shank with a cross wise handles for turning and having

central tapered feed screw.

The augers can be operated manually as well mechanically.

The hand auger used for boring is about 15cm to 20cm in diameter. These

are suitable for advancing holes up to a depth of 3 to 6 m in soft soils.

Mechanical augers are driven by power and are used for hard strata.

For depths greater than 12m they become inconvenient.

Auger boring is generally used in soils which can stay open without

causing or drilling mud. Clay, silts and partially saturated sands can stand

un supported.

The investigations are done quite rapidly and economically by auger

boring.

The main disadvantage of the auger boring is that the soil samples are

highly disturbed.

Further, it becomes difficult to locate the exact changes in the soil strata.




AUGER BORING

WASH BORING In wash boring the hole is drilled by first driving a casing about 2 to 3 m

long and then inserting into it a hollow drill rod with a chisel shaped

chopping bit at its lower end.




Water is pumped down the hollow drill rod which is known as “wash pipe”.

Water emerges as a strong jet through a small opening of the chopping

bit.

The hole is advanced by a combination of the chopping action and the

jetting action as the drilling bit and the accompanying water jet disintegrate

the soil.

The water and the chopped soil particles rise upward through the annular

space between the drill rod and the casing. The return water also known

as wash water is laden with the soil cuttings. It is collected in a tub through

a T- shaped pipe fixed at the top of the casing. The hole is further

advanced by alternately raising and dropping the chopping bit by a winch.

The process is continued even below the casing till the hole begins to

cave in. at that stage the bottom of the casing can be extended by

providing additional pieces at the top.

The wash boring is mainly used for advancing a hole in the ground.

The equipment used in wash boring is relatively light and in expansive.

The main disadvantage of the method is that it is slow in stiff soils and

coarse grained soils.




WASH BORING

SPLIT SPOON SAMPLERS:

The most commonly used sampler for obtaining a disturbed sample of the

soil is the standard split spoon sampler.

It consists mainly of three parts ie; driving shoe made of tool steel, about

75mm long, steel tube about 450mm long, longitudinally in two halves and

coupling at the top of the tube about 150 mm long.

The inside diameter of the split spoon is 38mm and the outside dia. Is

50mm.

The coupling head may be provided with a check valve and 4 venting

ports of 10mm diameter to improve sample recovery.

This sampler is also used in conducting standard penetration test.

After the bore hole is made the sampler is attached to the drilling rod and

lowered into the hole

The sample is collected by jacking or forcing the sampler into the soil by

repeated blows of a drop hammer. The sampler is then withdrawn.

The split tube is separated after removing the shoe and the coupling and

the sample is taken out.

It is then placed in a container, sealed and transported to the laboratory.







SPLIT SPOON SAMPLER

SCRAPER BUCKET SAMPLER:

If a sandy deposit contains pebbles it is not possible to obtain samples by

standard split spoon sampler. The pebbles come in between the springs

and prevent their closure. For such deposits a scraper bucket can be

used.

A scraper bucket sampler consists of a driving point which is attached to

its bottom end,

There is a vertical slit in the upper portion of the sampler.

As the sampler is rotated, the scrapings of the soil enter the sampler

through the slit. When the sampler is filled with the scrapings it is lifted.

Although the sample is quite disturbed it is still representative of the soil.

A scraper bucket sampler can also be used for obtaining the samples of

cohesion less soils below the water table.




SCRAPER BUCKET SAMPLER




SHELBY TUBES AND THIN WALLED SAMPLERS:

Shelby tubes are thin wall tube samplers made of seamless steel. It is

used to obtain undisturbed sample of clay.

The outside diameter of the tube may be between 40mm to 125mm.

The commonly used samplers have the outside diameter of either 50.8mm

or 76.2mm. the bottom of the tube is sharpened and beveled which acts

as a cutting edge.

The area ratio is less than 15% and the inside clearance is in between

0.5% to 3%.

The length of the thin walled sampler tube is 5 to 10 times the diameter for

sandy soils and 10 to 15 times the diameter for clayey soils.

The diameter varies between 40 to 125mm and the thickness varies from

1.25 to 3.15mm.

The sampler tube is attached to the drilling rod and lowered to the bottom

of the bore hole. It is then pushed into the soil

After some time the tube is taken out and its ends are sealed before

transportation.







SHELBY TUBES AND THIN WALLED SAMPLERS

PISTON SAMPLER:

A piston sampler consists of a thin walled tube with a piston inside.

The piston keeps the lower end of the sampling tube closed when the

sampler is lowered to the bottom of the hole.

After the sampler has been lowered to the desired depth the piston is

prevented from moving downward by a suitable arrangement which differs

in different types of piston.

Then thin tube sampler is pushed past the piston to obtain the sample.

The piston remains in close contact with the top of the sample.

The presence of the piston prevents rapid squeezing of the soft soils into

the tube and reduces the disturbance of the sample.

A vacuum is created at the top of the sample which helps in retaining the

sample.




During withdrawal of the sampler, the piston provides protection against

the water pressure which otherwise would have occurred on the top of the

sample.

Piston samplers are used for getting undisturbed soil samples from soft

and sensitive clays.




PISTON SAMPLER




BORE CHARTProject : location:

Ground surface level: Bore No:

Type of boring : Soil sampler used:

Diameter of boring: date of start:

Ground water table: completion date:

Scale

in mt.

Description

of strata

Depth

from

GL in

(m)

Depth of

disturbed

sample

in(m)

Depth

of

undisturbed

sample

in (m)

Depth of

S.P.T

(m)in N

Blows for 300 mm

remark




EXPERIMENT NO: 7

FREE SWELL AND SWELL POTENTIAL




FREE SWELL AND SWELL POTENTIAL

OBJECTIVE:To determine the free swell index and swelling characteristics of soil

PROCEDURE:Two oven dry soil samples, 10 g each, passing a 425 micron sieve are

placed separately in two 100 ml gradated glass cylinders. Distilled water is filled in one cylinder and kerosene (A non polar liquid) in the other cylinder upto the 100 ml mark. The final volume of soil read after 24 hours (or more).

OBSERVATION:Initial in 100 ml Final in 100 ml

After 24 hours or moreFree swell

IndexSoil Volume

in waterSoil Volume in

KeroseneSoil Volume in water (x)

Soil Volume in Kerosene(y) (x-y/y)*100

SWELLING POTENTIAL:Swelling potential can be defined as percentage swell of laterally confined

sample on soaking under 6.9 kpa surcharges after being compacted to maximum dry density at optimum moisture content.

CALCULATIONS:For natural soil having clay upto 8 to 65 %.Swelling potential, Sp = 2.16 x 10-3 (Ip)2.44Where Ip = Plasticity IndexFor Black cotton soils,Swelling potential, Sp = 1/63 (Is)1.17Soil Mechanics Lab Manual - 69 -



Where Is= WL- Ws = Shrinkage Index

