6. Progress of the failure in different pillar ratios

Different loading conditions varying from the quasi-static to dynamic loading has been applied to the coal pillar with the different width to height (w/h) ratio to determine the pillar capability as well as the possible observed failure modes. A strain-based criterion, as a major failure criterion, was implemented in the ABAQUS/Explicit to predict of the cracking path due to the different applied loadings as well as different pillar geometrical properties. A quarter

Figure 6. Failure mode of a single pillar with the different w/h ratios.

coal pillar model based on the symmetrical boundary conditions with respect to the different width by height (w/h) ratios of 1–10 were developed. It was observed that when the w/h ratios are less than 4, the failure mode of pillar can be either a double or a single diagonal shear failure in which the trajectory cracking starts from the edges and progresses towards the centre of the pillar. While the w/h ratios are greater than 4, the obtained possible failure mode would be a combination of the shear and compression failure modes. Thus, the trajectory of the cracking due to the pure compression failure would be propagated from the centre to the corners where a pillar gradually starts towards fully squashed (see Figure 6).
