The following assumption is generally made.
- The stress system is assumed to be two dimensional i.e. the stress in the third direction is taken as zero.
- It is assumed that the coulomb equation for shear strength is applicable and the shear strength parameters C and ɸ are known.
- It is further assumed that the seepage conditions and water travels are known and corresponding pore water pressure can be estimated.
- The conditions of plastic failure are assumed to be satisfied along the critical surface. In other words, the shearing stress at all points of the critical surface area is large enough to mobilize all the available shear strength.