Application of a Brittle Failure Model to Assess Roof Stability in Coal Mine Entries

Stress-driven instability of roof rocks in coal mine entries can result in large roof falls with associated safety hazards. Failure may be related to spalling, cutter formation, and delamination of bedding of the roof strata. The mode of failure is similar to failure of brittle rocks observed in hard rock environments. Additionally, coal mine roof rocks and coal materials can exhibit brittle failure characteristics when tested in the laboratory. A brittle failure criterion that considers both extensional fracturing under low confinement as well as shear failure under increased confinement is applied in numerical models of coal mine entries. The results show that such models can replicate field-monitored rock mass deformations and depths of failure. The results further show that the predicted zone of extension failure resembles the “softening zone” that is described in coal mine roof support literature. The authors conclude that modeling the presence of a reduced strength extension failure zone produces a satisfactory simulation of rock response around coal mine entries.