Experiment No. 11: Soil Triaxial Compression
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Object
Determination of shear strength parameters of soils under triaxial loading conditions.

Apparatus
Triaxial cell, Compression machine, Cell pressure application system, Pore pressure measuring device, Volume change measuring device, Proving ring, Deformation dial gauge, Split mould, Trimming knife, Rubber membrane, Membrane stretcher, Rubber O' rings, Balance, Apparatus for moisture content determination.

Procedure
1. Prepare a test specimen of necessary diameter and length, and measure its weight. Place a rubber membrane around the specimen using the membrane stretcher.

2. De-air the outlet line at the pedestal of the triaxial base, place on its top a saturated porous stone with a filter paper disc, and then position the soil specimen with the membrane stretcher around it.
Put a loading cap on the specimen top, and seal the membrane on to the bottom pedestal and the top cap with O' rings.

3. Assemble the triaxial cell with the loading ram initially clear of the top cap. Fill the cell with water, raise the water pressure to the desired value, and maintain the pressure constant. Raise the platform of the compression machine to bring the ram in contact with the seat on the top cap.

4. Set both the proving ring dial gauge and the deformation dial gauge to zero, select an axial strain rate, and verify that the cell pressure remains constant.

5. For undrained shearing of saturated samples, either close the outlet valve at the base of the cell or connect it to a pore pressure transducer. For drained shearing of saturated samples, connect the outlet to a burette for volume change measurements.

6. Apply axial compression load and take readings of the proving ring at intervals of 0.20 mm vertical deformation till the peak load has been passed, or till the strain reaches 20% of the specimen length. Record also burette or pore pressure readings, as applicable.

7. Remove the axial load, drain the water from the cell, remove the specimen, make a sketch of the failure pattern, and take soil samples for water content determination.

8. Repeat the test on identical soil specimens under different cell pressures.

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