Numerical Simulation of the Stress Effects on the Cavity Growth Process in UCG Considering Two Random Parallel Coal Cleats

ABSTRACT The underground coal gasification (UCG) method might convert potentially abandoned sources of coal to utilizable mines. In this study, the effect of stress and configuration of two pre‐existing cleats in a brittle coal on the mechanism of secondary crack propagation and cavity growth rate has been investigated using the linear parallel bond model (LPBM). The numerical modeling results showed that the best situation for the coalescence phenomenon is at the cleat's tip to tip angle of 20°, the bridge angle and the step angle equal to 15° and 90°, respectively. Also, the rock bridge lengths had no effect on the geomechanics parameters. If cleats' spacing was almost equal to half of the initial crack length, the highest wing crack length would be achieved. On the other hand, samples fragmentations and number of cracks increase as the confining pressure increases; this is the more appropriate condition for the cavity growth rate.