EXPERIMENT 10 , Test Name: DIRECT SHEAR TEST , soil and foundation
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Purpose
This test is performed to determine the consolidated-drained shear strength of a sandy to silty soil. The shear strength is one of the most important engineering properties of a soil, because it is required whenever a structure is dependent on the soil’s shearing resistance. The shear strength is needed for engineering situations such as determining the stability of slopes or cuts, finding the bearing capacity for foundations, and calculating the pressure exerted by a soil on a retaining wall.
UEquipment
1. Direct shear device,
2. Load and deformation dial gauges,
3. Balance
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d- Test Procedure:
1. Weigh the initial mass of soil in the pan.
2. Measure the diameter and height of the shear box. Compute 15% of the diameter in millimeters.
3. Carefully assemble the shear box and place it in the direct shear device. Then place a porous stone and a filter paper in the shear box.
4. Place the sand into the shear box and level off the top. Place a filter paper, aporous stone, and a top plate (with ball) on top of the sand
5. Remove the large alignment screws from the shear box! Open the gap between the shear box halves to approximately 0.025 in. using the gap screws, and then back out the gap screws.
6. Weigh the pan of soil again and compute the mass of soil used.
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7. Complete the assembly of the direct shear device and initialize the three gauges (Horizontal displacement gage, vertical displacement gage and shear load gage) to zero.
8. Set the vertical load (or pressure) to a predetermined value, and then close bleeder valve and apply the load to the soil specimen by raising the toggle switch.
9. Start the motor with selected speed so that the rate of shearing is at a selected constant rate, and take the horizontal displacement gauge, vertical displacement gage and shear load gage readings. Record the readings on the data sheet. (Note: Record the vertical displacement gage readings, if needed).
10. Continue taking readings until the horizontal shear load peaks and then falls, or the horizontal displacement reaches 15% of the diameter
e- Analysis:
1. Calculate the density of the soil sample from the mass of soil and volume of the shear box.
2. Convert the dial readings to the appropriate length and load units and enter the values on the data sheet in the correct locations. Compute the sample area A, and the vertical (Normal) stress sv.
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Where: N = normal vertical force, and Sv = normal vertical stress
4. Plot the horizontal shear stress (t) versus horizontal (lateral) displacement? H.
5. Calculate the maximum shear stress for each test.
6. Plot the value of the maximum shear stress versus the corresponding vertical stress for each test, and determine the angle of internal friction (F) from the slope of the approximated Mohr-Coulomb failure envelope.
EXAMPLE DATA
Date Tested: MAY 26, 2022
Tested By: HM Class, Group A
Project Name : HM Lab
Sample Number : A, B , C
Visual Classification: Brown uniform sand Shear Box
Inside Diameter: 6.3 cm Area (A): 31.17 cm2 = 4.83 in2
Shear Box Height: 4.9 cm Soil Volume: 119.9 cm3
Initial mass of soil and pan: 1000. g
Final mass of soil and pan: 720.82 cm
Mass of soil: 279.18 g
Density of soil: 1.65 g/cm3
Direct Shear Test Data Displacement rate: _______
Normal stress: 2.27 psi
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