An Empirical Method for Predicting the Strength of Bim Materials Using Modifications of Lindquist’s and Leps’ Approaches

Abstract

The preparation of undisturbed representative samples for testing is almost impossible for geological masses such as jointed rock masses, rock accumulations and block-in-matrix-rocks (bimrocks). In this regard the work of Lindquist (1994) on the strength evaluations (and of Medley (1994) on characterization) of bimrocks are now regarded as pioneering research. Subsequent literature confirms the fundamental outcome of Lindquist’s work that when the volumetric block proportion (VBP) in a bimrock increases, the internal friction angle increases and the cohesion decreases. Further: the strength of blocks does not influence overall strength of bimrock – instead due to the strength contrast between strong blocks and weak matrix, the blocks force failure surfaces to pass tortuously around the blocks. More recent work (Sonmez et al. 2018) emphasized that under sufficient normal or confining stress conditions, the failure surfaces may also penetrate into the blocks for block-rich bimrocks with block to block contacts. Therefore, non-linear shear strength envelopes may be expected for especially block-rich bim materials such as rock accumulation (or rockfill) and jointed rock masses. In this study, a modification was introduced to Lindquist’s procedure by incorporating Leps’ (1970) non-linear shear strength envelope for rockfill (or rock accumulation) to model the strength of completely blocky accumulated rock materials (VBP goes to 100%). The modified Lindquist approach was tested by determination of the factors of safety of hypothetical models of bimslopes.