Problem: A soil sample is subjected to a tri-axial test where the measured hydrostatic stress is 450 kPa; the applied deviator stress is 460 kPa; and the measured water pressure is 80 kPa. The soil has material properties of cohesion of 80 kPa and the internal angle of friction of 23 degrees. Determine:

Part A: Angle of the failure plane.

Part B: Principal normal stress.

Part C: Principal shear stress.

Part D: Effective normal stress.

Part E: Shear strength.

Rework your solution from the beginning and check each step carefully.