STABILITY CHART FOR ZERO TENSILE STRENGTH HOEK-BROWN MATERIALS : THE VARIATIONAL SOLUTION AND ITS ENGINEERING IMPLICATIONS

Most conventional slope stability calculations are based on the linear Mohr-Coulomb failure criterion. A substantial amount of experimental evidence suggests however that failure criterion of most soils is not linear particularly in the range of small normal stresses. Particulate media like soils usually have very small tensile strength; and the present work focuses attention on zero tensile strength materials obeying a limiting form of the non-linear Hoek and Brown empirical strength criterion. Previous investigations of the effect of strength function non-linearity on results of slope stability calculations were based on limiting equilibrium procedures that include various approximations and static assumptions. The present study presents complete results (safety factors and failure modes) of a rigorous variational limiting equilibrium analysis which does not include kinematical or static assumptions. Linear and non-linear failure criteria depend on different strength parameters and significant comparison of the effect of strength function non-linearity on stability of slopes is possible only for a given state of experimental information (i.e. a given data set). By performing such a comparison it is shown that strength function non-linearity has very significant effect on the results of slope stability calculations for relatively steep and very gentle slope inclinations. In both of these inclination ranges the non-linear analysis results in conservative slope design compared with the conventional Mohr-Coulomb criterion. In the range of intermediate slope inclinations, analysis based on the Mohr-Coulomb criterion is acceptable, resulting in more conservative results than the present non-linear analysis.