Experimental and numerical study on the effect of calcite on the mechanical behaviour of coal

• Effect of calcite grains on the mechanical behaviour was evaluated through experimental tests and numerical simulation.
• The presence of calcite increases the Young's modulus, reduces the peak strength and the post-peak brittleness of the coal.
• High heterogeneity caused by calcite grains is the contributor to the deformation and failure characteristics of the coal.

The effects of the presence of calcite grains on the mechanical behaviour of a coal are investigated in this study. Coal specimens with and without calcite grains were obtained from the same coal seam and then subjected to confined compression with varying confining pressures. Mineral composition data of the coal containing calcite grains were obtained from petrographic analysis and subsequently used for constructing UDEC-GBM model. The model was calibrated to experimental results and then used to further the understanding of the influence of calcite grains on the mechanical behaviour of the coal. It is found that the presence of calcite increases the Young's modulus, reduces the peak strength and the brittleness of the coal. The numerical results suggest that the presence of calcite grains significantly increase the heterogeneities of the coal, leading to differential and extensional straining which in turn causes internal tensile stresses and consequently tensile cracking. The conformity of the numerical results with the experimental observations suggests the potential use of the UDEC-GBM approach model for better understanding the mechanics of brittle rock failure at micro-structure scale.