Many design codes recommend using the limit states design in different geotechnical design applications including rock slope stability. The Generalized Hoek-Brown (GHB) failure criterion is widely adopted for rock characterization. However, a partial factor is defined for the uniaxial compressive strength only in international codes like the Eurocode. The limit states slope stability using the reduced uniaxial compressive strength does not provide the same factor of safety when the reduced equivalent Mohr-Coulomb (MC) parameters are utilized in the analysis. This study aims at developing a partial factor for the Geological Strength Index such that the limit states design of weak rock slopes using the reduced GHB parameters becomes equivalent to the design using the reduced MC parameters. A parametric study has been carried out using the Limit Equilibrium Analysis approach for weak rock slopes considering several parameters such as the uniaxial compressive strength, the geological strength index, slope inclination and height, and water depth. It is concluded that the proposed partial factor should range from 1.10 to 1.15 according to the values of the uniaxial compressive strength and geological strength index. These two parameters are the most influential on the proposed partial factor.

1. Introduction

Hoek-Brown (HB) criterion has been utilized for over three decades to characterize the failure envelope of rock mass [1]. It has gained a lot of attention from rock mechanics researchers and practitioners due to its ability to quantify the effect of discontinuities on the rock mass strength, especially weak rocks [2]. Hoek et al. [3, 4, 5] defined the rock mass strength by two main parameters, the Uniaxial Compressive Strength (σ ci) and the Geological Strength Index (GSI).

Limit equilibrium analyses (LEA) of rock slopes have been carried out for a long time using equivalent Mohr- Coulomb (MC) parameters (cohesion "c" and friction angle "Φ"). The equivalent MC parameters are determined by linear interpolation of the inherently-nonlinear GHB failure envelope in the same expected range of confining stresses. With the recent advances in the geotechnical software applications, it became now possible to carry out the LEA utilizing GHB parameters.

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