Rock Mass Strength Considerations in Rock Masses With Networks of Weak Veins

Limited work has progressed on strength estimation in weak veined rock (WVR) masses which are those containing networks of veins that are of low strength and have a rock block compressive strength <25MPa. In this paper, the characterization of a WVR is presented. First the WVR is introduced and its characteristics outlined. Then, an overview of the available methods for assessing rock mass strength are presented to show the limitations of these methods in veined and especially WVR. The low strength estimates at both low and high confining pressures obtained by using the HB-GSI equations are highlighted. Factors identified as impacting rock block interlocking (i.e., vein bounding intra-block rock strength, vein peak cohesion, and vein residual friction angle) are then assessed using two-dimensional numerical stress modelling to determine their relative impact on both the unconfined and confined veined rock block strength. The results show that confined strength rapidly increases due to intra-block interlocking in veined rock blocks suggesting that the HB-GSI strength estimation equations significantly underestimate the strength of veined rock blocks when confined. Particle size distributions are investigated to determine if they can be used to assess areas of higher or lower interlocking in the rock mass. The results suggest that the particle size distributions do change depending in the competency of the WVR and are valuable for assessing the spatial variability of WVRs. The work presented in this article can be used to improve the reliability of characterizing WVRs and corresponding strengths.