Abstract

Recently, the Hoek-Brown failure criterion is one of the mostly used failure criterion for rock mass. The constants of this failure criterion depend on, among the others, the Geological Strength Index (GSI) and the disturbance factor (D). The purpose of this paper is to analyze the sensitivity of the various constants of this equation, which depends on the GSI value and the D factor. The results show that the Hoek-Brown constants are very sensitive to both the GSI and the D factor, so to determine them exactly is very important for the rock engineering design. The sensitivity of the strength of the rock mass is also calculated. Thus these input parameters can be not determinable exactly, the results shows to take into account to use these relationships, mostly for risk analysis.

1 Introduction

The purpose of this paper is to determine the sensitivity of the Hoek-Brown failure criterion of rock mass based on the Geological Strength Index (GSI) and the disturbance factor (D). The sensitivity of different empirical formulas to parameter uncertainty is an important factor for a rock engineering designer.

The Hoek-Brown rock mass failure criterion is frequently applied in rock engineering calculations one should have some idea about the effect of variations in the input parameters for judging the acceptability of the design. Accordingly, we analyze the generalized Hoek-Brown formula from this point of view, and give some practical tools for rapid sensitivity analyses.

The first steps of this analysis were carried out by Ván & Vásárhelyi (2007). According to their results, the GSI based equations for calculating the deformation moduli of rock mass (Hoek & Diederichs 2006) can be not used in the practice without any risk.

It has to be noted, that the origin of all of these GSI based equations is empirical, they do not have any theoretical foundation. Moreover, their empirical foundation is questionable, it was never published, as it was pointed out by Anagnostou & Pimentel (2012). Recently, Ván & Vásárhelyi (2013) analyzed the advantage and disadvantage of the GSI system.

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