This lesson describes the differences between geostatic and induced stresses in the soil. We use Mohr's circle to compute the normal and shear stresses acting within a soil element along a plane of any orientation. Equations are provided to compute the normal and shear stresses acting on any plane within a soil element. Equations are also provided to compute the principal stresses and orientation of the principal planes in a soil element. The concept of the pole or origin of planes is presented, and two examples are provided that show how the pole can be used to compute the stresses acting on any plane within a soil element.

Learning Objectives:
1) Explain the differences between geostatic and induced stresses in the soil.
2) Use Mohr's circle and/or equations to find (a) the principal stresses in a soil element, (b) the orientation of the principal planes, and (d) the normal and shear stresses acting on any plane through a soil element.