ANS:B - Failure plane does not carry maximum shear stress

Only in the case of pure clay where phi = 0 failure plane carries max shear stress, in every other case fails at a shear stress less than max shear stress. Shear stress does not cause failure of plane. Due to max normal stress should makes failure in plane. Failure plane may not carry max shear stress because in box shear test or direct shear test the failure plane may not carry max. Shear stress.