Distinct element method simulation of an analogue for a highly interlocked, non-persistently jointed rockmass

Abstract

A grain-based distinct element model is used to reproduce the laboratory response of both intact and granulated Wombeyan marble. The term "granulated" refers to a heat treated marble where the cohesion of grain boundaries has been destroyed. The unconfined compressive strength of granulated marble is less than 50% of that of intact marble, while the strength of the granulated marble increases to about 80% of that of the intact marble at higher confining stresses. An iterative calibration approach is developed to match the unconfined and confined strengths of the models to those of intact and granulated marble. The simulation test results of the models of intact and granulated marble including the transition in the failure mode, stress-strain response, and the evolution of inter-and intra-grain micro-cracks with increasing confinement are discussed. The observed rapid strengthening effect, in terms of increasing confinement, is interpreted to be due to the high degree of grain assembly geometric interlock, which arises from the tight fit geometric shape of the grains as well as the roughness of the grain boundaries. It is suggested that the granulated marble can be considered to be an analogue for a highly interlocked, non-persistently jointed rockmass. It is shown that when the generalized Hoek-Brown failure criterion and the Geological Strength Index (GSI) are used to match the strength of the granulated marble at zero confinement, the confined strength of the granulated marble is underestimated by as much as a factor of two. Therefore, the confined strength of a highly interlocked, nonpersistently jointed rockmass, with strong, brittle rock blocks, could be significantly higher than that predicted by commonly adopted empirical approaches. This has practical implications for the design of highly confined pillars and abutments, which is discussed in this paper.

Influence of grain size heterogeneity on strength and microcracking behavior of crystalline rocks

“…(d) Grain‐based model consisting of discs bonded together with parallel bonds (black) inside the grains and smooth‐joint contacts (red) along the interfaces between the grains (reproduced from Potyondy [] and Bahrani et al . []).…”

“…Illustration of disc movements after breakage of (a) parallel bond and (b) smooth‐joint contact [after Bahrani et al ., ].…”

“…The procedure of generating a grain-based model in PFC2D is not presented here. Interested readers can refer to Potyondy [2010] or Bahrani et al [2014] for more details. One merit of the PFC2D grain-based model Journal of Geophysical Research: Solid Earth 10.1002/2016JB013469 is that the model can not only simulate the microcrack initiation and interaction at the grain boundary but also capture the microcracking behavior inside the grains which is associated with intragranular microcracking.…”

A grain based modeling study of mineralogical factors affecting strength, elastic behavior and micro fracture development during compression tests in granites

“…This mimics the real microstructure of crystalline rocks more closely and allows matching the ratio between unconfined-compressive strength and direct-tension strength more closely, as well [39]. Recently PFC2D GBM studies have been conducted [40][41][42][43], however, while the ratio between direct tensile strength and unconfined compressive strength could be matched by the GBM approach, the Brazilian tensile tests and unconfined compression test results can still not be reproduced with the same model when only one mineral type is considered in the model [43]. Therefore, four different mineral types are explicitly modeled in this study.…”

“…All compression tests were initially performed with constant Parallel-bond (a) and smooth-joint contact (b) and particle movement after bond/contact breakage (c and d) [42]. displacement and additionally with crack rate controlled displacement to evaluate the effect of continuous versus stepwise displacement on the fracture patterns in compression tests.…”