(a) A sample of cohesionless sand, whose friction angle is 33, is subjected to direct shear testing as shown on Figure Q-4. The sand fails when the shearing stress reaches a maximum value of 156 kPa. (i) What is the applied vertical pressure (due to the normal force N) acting on the soil sample? [2 marks] (ii) Determine, using Mohr's circle or otherwise, the magnitude of the principal stresses acting on a soil element X located near the horizontal failure shear plane (dashed line) as shown on Figure Q-4. [6 marks] DX Figure Q-4 AV cohesionless sand (b) The same cohesionless sand of part (a) is next subjected to consolidated drained (CD) triaxial testing in compression. The sample fails when the axial pressure (which includes the confining pressure) acting on the sample is 408 kN/m. What is the confining (cell) pressure used in this CD test? [5 marks] (c) The same cohesionless sand of part (a) is next subjected to consolidated undrained (CU) triaxial testing in compression. The sample fails when the deviator pressure acting on the sample is 153 kN/m and the excess pore pressure at failure is 136.6 kN/m. What is the confining (cell) pressure used in this CU test? [7 marks]