Stress analysis in failed roof at a longwall face

This paper presents a conceptual work on roof failure mechanisms at a longwall coal mining face based on a multiple sliding block model. Underground observations of the caved roof strata at the longwall face indicate that many types of fracture exist and that two are dominant. In response to roof convergence close to the goaf, the stratified ground flexes resulting in shear failure along the weak bedding planes that are present in sedimentary strata, while sub-vertical fractures form just ahead of the longwall face in response to the mining induced stress state. . These mining induced fractures usually occur at regular intervals during the mining face advance forming a typical blocky appearance within the roof strata. During roof movement interaction between the blocks occurs along the horizontal and near vertical fracture planes, this interaction can induce large stresses at the block boundaries at the roof level. Analytical and computational calculations attempt to interpret this movement and explain the stress distribution within the broken roof that results in high stress concentrations at the roof level. These stress concentrations can fail the already weakened roof strata leading to roof cavities that can seriously disrupt the longwall mining operation.