Experiment No. 9: Soil Direct Shear Test
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Determination of shear strength parameters of a silty or sandy soil at known density and moisture content.

Shear box with clamping screws, Box container, Porous stones, Grid plates (serrated and perforated), Tamper, Balance, Loading frame, Proving ring, Deformation dial gauges, Apparatus for moisture content determination.

1. Measure shear box dimensions, set up the box by fixing its upper part to the lower part with clamping screws, and then place a porous stone at the base.

2. For undrained tests, place a serrated grid plate on the porous stone with the serrations at right angle to the direction of shear. For drained tests, use a perforated grid over the porous stone.

3. Weigh an initial amount of soil in a pan. Place the soil into the shear box in three layers and for each layer apply a controlled amount of tamping with a tamper. Place the upper grid plate, porous stone and loading pad in sequence on the soil specimen. Weigh the pan again and compute the mass of soil used.

4. Place the box inside its container and mount it on the loading frame. Bring the upper half of the box in contact with the horizontal proving ring assembly. Fill the container with water if soil is to be saturated.

5. Complete the assembly, remove the clamping screws from the box, and initialize the horizontal displacement gauge, vertical displacement gauge and proving ring gauge to zero.

6. Set the vertical normal stress to a predetermined value. For drained tests, allow the soil to consolidate fully under this normal load. Avoid this step for undrained tests.

7. Start the motor with a selected speed and apply shear load at a constant rate of strain. Continue taking readings of the gauges until the horizontal shear load peaks and then falls, or the horizontal displacement reaches 20% of the specimen length.

8. Determine the moisture content of the specimen after the test. Repeat the test on identical specimens under different normal stress values.

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