A modelling approach consisting of best-fit relations to estimate the post-yield strength parameters is presented for simulating post-peak behavior beyond the point of residual strength of coal pillars having different w/h ratios. The model was developed based on back-analysis of the complete stress-strain behavior of specimens belonging to six different Indian coal seams with different w/h ratios of 0.5–13.5. It was found that the simultaneous degradation of the cohesion and friction angle of the Mohr-Coulomb rock material characterizes the post-peak strength behavior of the rock. The resulting expressions are simplistic as they require parameters that can be easily determined using uniaxial and triaxial compression results. Eventually, the developed model was validated by simulating the triaxial tests of coal specimens with different sizes under varying confining stresses and comparing its findings with the published test results. The study showed that its implementation in the numerical model could reproduce laboratory-observed mechanical response, deformation behavior, and failure mechanism very closely.

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Keywords: Strain softening, Dilatancy, Interface, Shape effect, Residual strength