ABSTRACT
In shear strength reduction technique the factor of safety (FOS) of a slope traditionally defined as the ratio of the actual shear strength to the minimum shear strength to prevent failure. The method was first used by Zienkiewicz et al. (1975) and later by Naylor (1981), Matsui and San (1992), Ugai and Leschinsky (1995), Griffith and Lane (1999), Dawson et al. (1999), Lechman and Griffiths (2000), Zhang et al. (2009) and many other researchers. In this method, the failure surface is automatically defined unlike conventional limit equilibrium. In the shear strength reduction technique it is assumed that failure mechanism of a slope is directly related to the development of the shear strain and the existence of the shear strength dependency of the strain. As the shear strain developed in the slope increases with reducing the shear strength, the existence of the shear strength dependency of the strain is also related with the stability of slope (Matsui and San, 1992). Criteria based on the shear strain better suit the need as it is usually difficult to find the failure slip surface based on stress failure criterion. It has been demonstrated by many researchers using laboratory tests that the failure shear strain zone usually coincided with the rupture surface (Roscoe, 1970). As the shear strain developed in the slope increases with reducing the shear strength, the existence of the shear strength dependency of the strain is also related with the stability of slope. Stability of the slope is a function of the shear strength and the development of failure strain reflects the potential failure zone of slope, the shear
strain developed in the slope increases with reducing the shear strength (Matsui and San, 1992).
