DETERMINATION OF SHEAR PARAMETERS OF SOIL BY TRIAXIAL TEST

By | July 16, 2017

DETERMINATION OF SHEAR PARAMETERS OF SOIL BY TRIAXIAL TEST

OBJECT OF EXPERIMENT


The object is to determine the shear parameters of soil with the help of triaxial compression apparatus by unconsolidated undrained test without measurement of the pore pressure.

DETERMINATION OF SHEAR PARAMETERS OF SOIL BY TRIAXIAL TEST

 

STANDARD REFERENCE


IS 2720 – PART – 13 – 1986

 

EQUIPMENTS


1. Triaxial cell

2. Pressure chamber fitted with valves with foot pump for applying and maintaining the desired fluid pressure in the cell.

3. Compression machine capable of applying axial compression to the specimen

4. Dial gauge to measure axial compression

5. Rubber membranes

6. Membrane stretcher

7. ‘O’ – Ring, 2 Nos

8. Split moulds

9. Trimming Knife

10. Balance

11. Stop watch

 

TEST PROCEDURE


A) PREPARATION OF UNDISTURBED TEST SPECIMEN

1. Collect the sample in the sample tube.

2. Extract soil sample from the sampling tube.

3. Cut the soil cake at the desired length.

4. Trim the sample to the correct size.

5. Transfer the sample from the tube to a split mould.

6. Grease the inside walls of the mould to avoid surface moisture loss.

B) PREPARATION OF REMOULDED TEST SPECIMEN

1. Remoulded sample may be prepared in a bigger mould by compacting the soil at the desired water content and dry density.

2. Alternatively, remoulded specimen may be prepared directly in the split mould. Apply grease to the mould to avoid surface drying during remoulding the specimen. The remaining steps to followed are same as it is stated for undisturbed specimen.

C)COMPRESSION TEST

1. Place the specimen assembly centrally on the pedestal.

2. Admit the operating fluid in the cell, and raise its pressure to the desired value. Adjust the loading machine to bring the loading ram a short distance away from the set on the top cap of the specimen. Read the initial reading of the proving ring dial gauge. Adjust the loading machine further so that the loading ram comes just in contact with the seat on the top of the specimen. Note the initial reading of the dial gauge.

3. Apply the compressive force at constant rate of axial compression, such that failure is produced in the sample with time. Take the reading of the load and deformation dial gauges simultaneously, plot the stress strain curve. Continue the test until the maximum value of stress has been passed or until  an axial strain of 20% has been passed.

4. Unload the specimen and drain off the cell fluid. Dismantle the cell and take out the test specimen. Remove the rubber membrane and note down the mode of failure. Weigh the specimen. Keep samples for water content determination.

5. Repeat the test on three or more identical specimen under different cell pressure.

 

OBSERVATIONS


A) Details of the soil specimens : Undisturbed / Remoulded soil

1. Initial diameter of the specimen (D0) : ……………. mm

2. Initial area (A0) : …………… cm2

3. Initial moisture content : …………… %

4. Initial length of specimen (L0) : ……………. mm

5. Volume of specimen : …………… cm3

6. Weight : …………… gm

B) Undrained triaxial test

1. Cell pressure (σ3) :

2. Corrected area (A) = A0/(1 – ϵ)

3. Proving ring dial gauge (LC) :

Dial gauge reading

(1)

Proving ring dial gauge reading

(2)

Strain (ϵ) %

(3)

Corrected area

(4)

Deviator force

(5)

Deviator stress,

σd = (σ1– σ3)

(6)

Therefore, From Graph :-

Failure Strain = ……………

Deviator Stress at Failure = …………….

Test No.

(i)

Cell Pressure

3)

(ii)

Deviator stress at failure

d ) = (σ1– σ3)

(iii)

σat failure

 

Test

Sample 1

Sample 2

Sample 3

Center [(σ1+ σ3)/2]

Radius [(σ1– σ3)/2]

 

CALCULATION


1. The deviator stress (σ1– σ3) or principle stress difference at any stage of the test is determined by dividing the additional axial load by the corrected area.

2. Use separate table for each test. Plot the deviator stress (σ1– σ3) and strain (ϵ) and find maximum deviator stress (σ1– σ3) and corresponding maximum strain.

3. The shear strength parameters are obtained from a plot of Mohr Circles.

From Graph : The cohesion (C) =…………….

The Angle of Internal Friction (ф) = …………….

 

REMARKS


Finally, write your own experience from experiment.

 

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