Abstract:

Empirical models are being frequently used to estimate rock mass mechanical properties. It is well known that most empirical methods in rock engineering give averaged values, and that it might be significant variation between the lowest and highest value. Besides, it is highly important to describe relations between input parameters in an empirical model if one wants to obtain accurate results during stochastic analysis. In this paper, we run two different Monte Carlo simulations for the comparison of results generated from empirical Hoek-Brown failure criterion. First simulation model assumes all input parameters used in the criterion as independent variables and second model includes the relationships between input parameters via a correlation matrix. The correlation matrix used in the simulations is succeeded by consulting knowledge of some experts in the field of rock engineering. It is found that with or without considering correlations, the mean values of simulation outputs computing the rock mass strength parameters are not notably different. However, the standard deviations of strength parameters are generally smaller in simulation results taking into account of correlations between input parameters. It is concluded that in a stochastic estimation study, defining the relationships between input parameters would not change the simulation results drastically.

1 INTRODUCTION

A rock mass is a system basically composed of two components; intact rock pieces and discontinuity network. Intact rock refers to unfractured blocks between structural discontinuities. A discontinuity is described as "a plane of weakness that has zero or low tensile strength or tensile strength lower than stress levels generally applicable in engineering applications" (Anon. 1977). Riedmuller & Schubert (1999) stated that complex properties of a rock mass could not sufficiently be described by a single number. Therefore, rock mass characterization and description are main issues in engineering geology and rock engineering.

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