The direct shear test is performed to determine the consolidated-drained shear strength of a soil. The shear strength is one of the most important engineering properties of a soil, as it is required whenever a structure is dependent on the soil’s shearing resistance.
Equipment & Materials * Direct shear apparatus and associated items * Electronic balance * Vernier calliper * Dry sand
Procedure 1. Carefully assemble the shear box and measure its diameter and the height 2. Measure the thickness of the top porous stone 3. Measure the initial mass of sand in the pan 4. Place the sand into the shear box and level it off. Place the top porous stone and measure the unfilled height of the shear box to calculate the thickness (height) of the sand sample in the shear box. 5. Place the top plate (with ball) on top of the sand 6. Measure the pan of sand again to compute the mass of sand used 7. Place the shear box in the direct shear apparatus and set the vertical load cell, vertical displacement transducer, horizontal load cell, horizontal displacement transducer in contact with the shear box. 8. Remove the alignment screws from the shear box 9. Apply the pre-determined vertical load (stress) using the computer. 10. Start the test with selected constant rate of shearing (0.1 mm/sec). 11. During shearing, record shear force, horizontal displacement, vertical displacement, and vertical load (which is maintained at a constant value) at every 5 sec. 12. Once the test in completed, release vertical load and shear load using the computer and take the shear box out from the apparatus. 13. Removed the sand in the shear box and clean the apparatus. 14. Use the data file saved in the computer for calculation and plotting
Calculations and Discussions 1. Completed and attached data sheet at the back of the report. 2. Dry density of the soil sample, p = MassVolume
Mass is given by:
Mass = Mass of the sand + pan (before use) – Mass of the sand + pan (after use)
= 169.36 – 85.67 = 83.69
Volume is given by:
Volume = Area × Height
Hence, the dry density of the soil sample is: p = MassVolume=83.6953.61=1.56gm/cm3 3. Vertical Normal Stress = Vertical Normal LoadArea of specimen = 200π×6324=64.15KPa 4. Computer generated sheet for shearing attached at the back. 5. The shear stress for the specimen can be calculated using the following equation:
Shear Stress = Shear LoadArea of specimen
The following calculation, =(1000*(Column C/3117.245)), was used in excel to generate a data column for shear stress. 6. Initialised values attached together with the computer generated sheet. 7. Shear stress versus shear displacement diagram are as follows:
Figure 2: Shear Stress vs Shear Displacement 8. From the graph above, the maximum shear stress is observed to be around 25KPa. This is backed up by the values obtained from Excel, where the maximum shear stress is 25.98KPa.
9. Using the maximum shear stress (25.98) and the normal stress (64.15), a plot was created. The Maximum Shear Stress vs Normal stress plot is attached at the back.
10. Angle of internal friction (θ) = tanθ=oppositeadjacent
Given that opposite = 25.98 and adjacent = 64.15, θ can be calculated:
θ=tan-125.9864.15, θ=22.04° 11. The internal friction angle plays an…