Q3. Three direct shear tests were conducted on samples of OC clay. The shear box was square of size 60 mm x 60 mm and the vertical force was kept constant during each test. The following forces and displacements were recorded for each sample at the moment of failure: Sample # Vertical Force, N Shear Horizontal Force, S displacement (-) (N) (N) (mm) 1 90 60 3.81 2 180 98 4.13 3 270 137 4.45 a). Plot the Mohr-Coulomb failure envelope for this soil and determine graphically the angle of internal friction, and the cohesion, c of the clay. (Hint: use the corrected sample area, Ac to calculate the normal and shear stresses.) On the same plot as in part a) and for Sample #2 (only): b). Draw the Mohr's circle at failure and determine graphically the magnitude of the major and the minor principal stresses and the orientation of the two principal planes. c). Determine graphically the orientation of the failure plane. 08 d). e). Determine graphically the magnitude of the maximum shear stress at failure and the orientation of the plane on which it acts. Describe the steps in the graphical solution for parts (a) to (d).