● Problem 4 The same sand as in Problem 3 is tested in a direct shear device under a normal stress of 390 kPa. The specimen fails at a shear stress of 260 kPa. a) Is the stress state at failure consistent with Problem 3? b) Compute the major and minor principal stress at failure (i.e., σ¹¹ƒ = 01f and σ¹³½³₁ = 03). c) What is the orientation of the failure plane (i.e., Of) and the orientations of the major and minor principal stresses at failure? d) Finally, draw the Mohr circle associated with failure. • Problem 3 In a consolidated drained (CD) axisymmetric triaxial test, a sand specimen is first isotrop- ically consolidated to a total stress of σ3 = 450 kPa. With this value of σ3 maintained con- stant, the specimen is next sheared with the drainage valve open. At failure, the principal stress difference (01-03) is equal to 1,121 kPa. a) Compute the major and minor principal stress at failure (i.e., σ'₁₁ = 01f and σ¹³½³₁ = 03₤). b) Next, determine the effective friction angle '. c) The normal and shear stress acting on the failure plane (i.e., σ'ff and Tƒƒ). d) What is the orientation of the failure plane (i.e., 0ƒ)? e) Finally, draw the Mohr circle associated with failure.