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. Test no. 1 2 3 4 2m 84 168 E 2.2 m 5.25 m 254 360 Figure 12.54 Normal force (N) 2.6 m 3.5 m Following are the results of four drained, direct shear tests conducted or clay samples with each having a diameter of 63.5 mm and height of 32 m G.W.T Shear force at failure (N) 28.9 59.6 Silty sand e=0.72; G,- 2.69 = 89.1 125.3 Silty clay w = 22%; G₁ = 2.72 Poorly graded sand Ysat 19.8 kN/m³ 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.