ABSTRACT:
Although tensile strength can often be neglected for weak or highly jointed rock masses, the strength of rock bridges in moderately fractured and blocky hard rock masses contributes significantly to their self-supporting capacity and should be considered in engineering design. This self-supporting capacity can often be attributed to the distributed load bearing capacity of rock bridges separating joint segments and fractures. A rock bridge provides an effective cohesion to the joint and a rock block cannot fall or slide until all the rock bridges fail. In this study, we generate various combinations of geometric conditions of discontinuities using UDEC. Non-persistent joints generated in the UDEC models are assigned distributed joint properties randomly. A degradation model is developed in UDEC to simulate the combined failure process of intact rock and joints. Equivalent rock mass strength considering joint persistence is obtained and compared to theoretical results. The objective is to analyze how the joint persistence will increase the overall rock mass strength in jointed hard rock masses, with the focus on the verification of a previously proposed approach to consider the influence of joint persistence on the rock mass strength by the concept of equivalent block volume in the GSI system.
1 INTRODUCTION
To provide a practical tool to estimate the rock mass strength for use with the Hoek-Brown failure criterion (Hoek & Brown 1980, 1988, Hoek et al. 2002), the GSI system was introduced (Hoek et al. 1995). The value of GSI ranges from 0 to 100. The GSI system consolidates various versions of the Hoek- Brown criterion into a single simplified and generalized criterion that covers all of the rock types normally encountered in rock engineering. A GSI value is determined from the interlocking structure and joint surface conditions.
