12.4 During a subsoil exploration program, undisturbed normally consolidated silty clay samples were collected in Shelby tubes from location A as shown in Figure 12.54. 2 m G.W.T Silty sand e=0.72: G, 2.69 2,2 m 3.5 m 5.25 m 2.6 m Silty clay w=22%; G, = 2.72 Poorly graded sand, Ysat 19.8 kN/m³ Figure 12.54 Following are the results of four drained, direct shear tests conducted on the clay samples with each having a diameter of 63.5 mm and height of 32 mm. Test no. Normal force (N) Shear force at failure (N) 1234 84 28.9 168 59.6 254 360 89.1 125.3 a. Determine the drained angle of friction for the silty clay soil. b. Determine the shear strength of the clay in the field at location A. D