Design of rock slopes using SSR classification system

Abstract

A new rock mass classification system called Slope Stability Rating (SSR) is presented. SSR classification is a development of the so-called Geological Strength Index (GSI) which has become known worldwide, and applied by many engineers and researchers as a systematic tool to describe rock mass conditions and determine the shear strength parameters. In addition to the modified Geological Strength Index (GSI), SSR considers five additional parameters which were uniaxial compressive strength of intact rock, rock type (lithology), slope excavation method, groundwater condition and earthquake force. Some simple design charts were provided by SSR which describe the relationships between the rock slope height and the SSR value versus the stable slope angle, for different factors of safety. The appropriate stable angle of the rock slope can be obtained accordingly. The new system was validated based on 46 slope case histories from Iran and Australia. Some guidelines are then provided to determine SSR value simply in the preliminary stages of the projects. SSR classification system with its relevant design charts can be applied as a useful empirical tool to evaluate the stability of heavily jointed and/or large-scale rock slopes prior to the application of more sophisticated design methods.