As shown in the figure, the maximum shear stress is equal to the half the diameter of Mohr's circle which is equal to 50 kPa. The angle at which the maximum shear stress acts with respect to the major principle stress is found by drawing a line from the pole for planes to the maximum shear stress point. This angle is equal to 45° .

Question – 6.4. Analyze the state of stress at a point, A , located few meters below the ground surface, in front of the civil engineering building of IIT Guwahati, Assam. The vertical normal stress at A is 400 kPa, and other principle stresses are 100 kPa and 50 kPa, respectively. The pore water pressure is expected to vary from -250 kPa to -50 kPa during the months of January and May. The principle stresses are estimated to decrease 10% in the month of May. Assume the pore air pressure to be at a zero reference value.

Solution : The net normal stresses at point A are

in January: kPa, and kPa.

in May:kPa.

The matric suction is kPa in the month of January and 50 kPa in the May. The state of stresses are given by drawing the Mohr's circle for the present stress state in the following figure.

Fig. 6.26 Mohr's circle representation of the state of stresses for problem 6.4