The following assumptions are generally made:

i) The stress system is assumed to be tow-dimensional i.e., the stresses in the third direction (perpendicular to the section of soil mass) are taken as zero.

ii) It is assumed that the coulomb equation for shear strength is applicable and the shear strength parameters C and ∅ are known.

iii) It is further assumed that the seepage conditions and water travels are known and the corresponding pore water pressure can be estimated.

iv) The conditions of plastics failure are assumed to be satisfied along the critical surface. In other words, the shearing strains at all points of the critical surface are large enough to mobilize all the available shear strength.