Finite element formulation was incorporated in the existing method of slope stability analysis using slices, and new formulations were derived. In the formulations, at first only the deformations developed in the slices were considered. It was assumed that the nodal displacements develop along the sliding surface. Also, the shear force and the normal force acting on the slope were considered as the nodal forces on an element. By introducing a factor of safety between the two forces, so that the Mohr-Coulomb failure criterion is satisfied, a new relationship was derived. The new formulations thus render a unique solution without having imparting any additional condition, which is necessary in the conventional slope stability analyses. The formulations are then re-derived taking the deformation of a pile also into consideration in the case of a slope reinforced with piles. Numerical analyses were performed for two slopes: one in which no stabilizing piles are present in the slope and the other with one stabilizing pile. Highly reliable values of the global factor of safety and the external nodal force could be obtained from the analyses.
Ensuring the stability of both natural and man made slopes still remains to be an important problem in geotechnical engineering discipline. There are many circumstances in natural slopes, compacted embankments and excavations where the geoteehnical engineer must investigate the stability of a slope by performing stability analysis. Such analysis should, therefore, be as insensitive as possible, to "a priori" conditions. Conventional methods of slope stability analysis using slices (Bishop, 1955; Janbu, 1957) are based on the limit equilibrium theorem, however, most of them render a statically indeterminate system. Therefore, in order to obtain a unique solution by using these methods, it is necessary to introduce additional conditions.
