In all indeterminate system, certain assumptions are required to solve the system and these assumptions depend on the analysis method. In analysis of soil mass the assumptions made are as follows:
a. A two-dimensional stress system is assumed in analysis, the stress components in third direction are considered as zero. Third direction means the stress along normal to section of soil mass?
b. Strength parameter cohesion intercept (C) and angle of internal friction (φ) are known.
c. Coulomb’s equation regarding shear strength is assumed to be applicable to this system.
d. The next assumption is water levels and seepage conditions of the soil mass are known.
e. Pore water pressure can be estimated based on (d).
f. It is assumed that plastic failure condition will be achieved along critical surface. Plastic failure condition means shear stress in any points of critical surface will be sufficiently large to become all obtainable shear strength mobilized.
g. In addition to the assumptions discussed above some assumptions are made depending upon method of stability analysis regarding forces distribution and their magnitude along anticipated planes.
Using these assumptions, the resultant forces and shear strength are determined. The factor of safety of slope is calculated using resulting forces available in the system and actuating forces.