Triaxial test

Triaxial test

xzDETERMINATION OF SHEAR PARAMETERS BY TRIAXAIL TEST

Aim: to determine the shear parameter of undisturbed soil specimen in the triaxail compression apparatus by unconsolidated, undrained test without the measurement of pore pressure.

APPARATUS

1. Triaxial Test Cell without transparent chamber capable of resisting internal fluid pressure of 1000 kN/m2.complete with all accessories.2. An Apparatus for Applying and maintaining the Desired Pressure on the Fluid Within the Cell to an accuracy 10 or 5 kN/m2.3. Compression machine, capable of applying axial compression to the specimen at convenient speed to cover the range 0.05 to 7.5 mm/min.4. Dail guage to measure axial compression accurate to 0.04.5. Seamless rubber membrane6. Membrane stretcher7. Rubber rings8. Split mould, trimming knife, wire saw meter straight edge, sample extruder, thin walled tubes, soil lathe. Meter box9. Water containment determination tins10. Balance11. Stop watch

THEORYSample preparation1. Undisturbed specimena) If the undisturbed sample has been collected in a thin walled tube having the same internal diameter as that of the specimen required for testing, the sample may be extruded out with the help of sample extruder, and pushed into the split mould. The sample should be extruded from the tube pushing from the cutting edge side. The ends of the specimen are trimmed flat and normal to its axis. The split mould should be lightly oiled from inside. The specimen is then taken out, carefully, from the split mould, and its length, diameter, weight should be measured to an accuracy enabling the bulk density to be calculated to an accuracy of plus or minus 1 percent. A portion of the soil trimmings is placed for water content determination. The specimen is then placed on one of the end caps and the other using the membrane stretcher. The membrane is sealed to the end caps by means of rubber rings. The specimen is then ready to be placed on the pedestal in the triaxial cell.b) If the undisturbed soil sample brought from the field is of large diameter than the specimen diameter, the sample may be cut to size either by means of thin walled tube or hand trimming or by a soil lathe. If a block sample has been obtained from the field, a rectangular prism slightly larger than the required final dimensions of the specimen is cut from the block sample. The ends of prism are made plane and parallel using meter box. The prism is then placed in the soil lathe, and excess soil is cut off in thin layers. The trimming operation, rotating the sample between end cutting operation, is continued until a cylindrical specimen results. The rest of the procedure for enclosing the specimen in the membrane etc., is the same as described in step (a).

2. Remoulded specimen. Remoulded samples prepared at the desired moisture and density by static and dynamic methods of compaction and then preparing the cylindrical specimen of required dimensions by the methods described in (b) above.

TEST PROCEDURE

1. Prepare cylindrical remoulded specimens by compacting the soil manually in the compacting apparatus at required water content.2. Trim the soil specimen by using trimming apparatus if necessary and trimmed specimen should be 76mm long and diameter should be 38mm3. The specimen is then closed in 38 mm dia. and about 100mm long rubber machine using the membrane stretcher. Spreading back the ends of the membrane over the stretcher and applying suction between the stretcher and the rubber. Stretcher is then easily slide over the specimen, suction is released and the membrane is unrolled from the ends of the stretcher. 4. Use non-porous stone on either side of the specimen as neither any pressure is not to be measured nor any drainage of air or water is allowed. 5. Remove the porous cylinder from its base removing the bottom fly nuts. 6. The pedestal at the center of the base of the cylinder on which the specimen is to be placed in cleaned and a 38 mm dia rubber 0-ring is rolled over to its bottom. The specimen along with the non-porous plate on either side is centrally placed over the pedestal and the bottom edge of the machine covering the specimen is sealed against the pedestal by rolling back the 0-ring over the membrane.7. The cap is placed over the top plate of the specimen and the top of the rubber membrane is sealed against the cap by carefully rolling over it another 0-ring. This arrangement of the rubber 0-ring forms the effective seal between the specimen with the membrane and the water under pressure. The specimen is checked for its vertically and co-axially with the cylinder chamber. 8. The chamber(cylinder) along with the loading plunger is carefully placed over its bases without disturbing the soil specimen and taking care to see that the plunger rest on the cap adjusted so that it just touches the plunger to by the naked eye. The chamber is than rotated if necessary such that the dial gauge recording that compression rests centrally over the top of the screw which can be locked at any level and which is attached to the top of the cylindrical chamber carrying the specimen. The cylinder is then attached to the base plate tightly by means of the tightening the nuts.

9. The valve to drain out the chamber and the valve to drain out the air and the water from the sample are closed and the air lock nuts at the top of the cylinder is kept open to facilitate the exit of air on the water enters the cylinder

10. The water storage cylinder is filled with water completely and its top is then closed by mean s of a valve. Desired pressure (50KN/m2) is built up in the cylinder by working the hand pump and pressure is maintained constant in the cell.

11. For this position, adjust the deformation dial gauge and proving ring reading to zero. 12. Record the initial readings of the proving ring and compression dial gauge. 13. The vertical load is applied to the specimen by starting the mortars at the loading frame. The change in the proving ring dial gauge gives the measure of the applied load. The deformation dial gauge gives the measures of the applied load. The deformation dial gauge gives the deformation in the soil specimen, which can be used to compute strains in the soil 14. Take the reading of proving ring dial gauge at 0.5, 1.0, 1.5, 2.0%(or any other smaller values)of the strain and for every 0.5% strain thereafter up to failure or 20% strain whichever is the earlier .

15. Throughout the test, make sure that the chamber, containing pressure is kept constant at the desirable values as indicated by the pressure gauge as the water cylinder.

16. After the specimen has failed or 20%strain is reached:-

a. Stop application of load b. Disconnect the chamber from the water storage cylindrically closing the lingers values c. Open the air lock knob a little d. Open the valves to drain out the water in the cylinder. After a few seconds, open the air lock nut of air at the top of the cylinder.

17. After the water is completely drained out, take out the cylinder from the loading frame carefully, loosen the nuts and remove the Lucile cylinder from its base without disturbing the sample.

18. Note the space of the failed specimen, angle of the shear plane if any and dimensions of the specimen.

FORMULAE

Where, Ao = initial area of the specimen normal to the axise = (Lo-L)/Lowhere, Lo = initial length of the specimen, andL = length of the specimen at the stage of test at which area is to be determined

The principal stress difference (1- ) for any stage of the test shall be determinedby dividing the additional axial load by the corresponding area A.

OBSERVATION

Soil specimen measurement:

initial length of specimen:76mm

Initial weight of specimen:

Initial diameter of specimen:38mm

cell pressure(3)=50KN/m2

load gauge constant:

Mode of failure:

Angle of shear plane with vertical axis:

Bulk density:

Moisture content:

Rate of strain:

OBSERVATION TABLE:

DisplacementIn dial gauge Reading(div)

Displacement(mm)

Strain*100(%)

Proving ring Reading(div)

Load(KN)

CorrectedArea()

Deviator Stress

()

Shear stress

()

Normalstress

()

000000000

500.50.661.20.02421.01610.50860.508

10011.316120.240.001149208.88104.44154.44

1501.51.974300.60.001157518.58259.29309.29

20022.632470.940.001165806.87403.44453.44

2502.53.289641.280.0011731091.22545.61595.61

30033.947811.620.0011811371.72685.86735.86

3503.54.605891.780.0011891497.06748.53798.53

40045.263751.50.0011971253.13626.57676.57

4504.55.92158.81.1760.00121971.9485.95535.95

Sample calculation:

Diameter of sampleHeight of sampleTherefore, area of sampleDisplacementLoadStrainCorrected area of sampleDeviator stressPrinciple stressMajor principle stressShear stressNormal stress=

Graphical representation

Shear stress vs nominal stress

Deviator stress vs strain

Result:1. Cohesion, Cu = 02. Angle of shearing resistance( u) = 32o3. Deviator stress at failure = 1497KN/m24. Shear stress at failure =798 KN/m25. Normal stress at failure = 756 KN/m2

Recommendation:Shear failure is diagonal. The soil used in this Triaxial test is found to be cohesion less as Cu=0. Since it is cohesion less it cannot be used for building purposes.

Practical reportPage 7