Floor heave in longwall gateroads is a severe issue that affects mining safety and efficiency. Researchers, however, have limited understanding on the floor heave mechanism because the deformation of post-failure rocks in the floor was seldom considered previously. In this study, we developed a theoretical model using the strain energy theory to investigate the post-failure deformation of rocks. This model was validated before being implemented into a numerical modelling package, FLAC3D, for floor heave analysis. Based on a case study of a longwall entry employing a stiff–yield pillar configuration, we observe that massive floor heave occurs at the entry rib that takes less loads (yield pillar) and eventually propagates towards the other rib bearing a significant amount of loads (stiff pillar). This observation sheds light on the floor heave mechanism in longwall gateroads and has major implications for coal mine ground control.

No abstract

The main entries in longwall coal mine frequently encounter large deformation, depending on the stress environment. Depressurizing boreholes are applicable to reduce the large deformation; however, it is difficult to determine the proper parameters (diameter and spacing) for an effective implementation. This study aims to propose feasible design criteria for the quantification of those parameters. We first developed a rigorous numerical model, for a roadway in Zhangshuanglou coal mine, using the rock mechanical properties determined from extensive laboratory measurements and analyses. We then investigated the dependency of the stress transfer and roadway deformation on the ratio of borehole diameter and spacing (D/R and D/I). The symbols of D, R, and I represented the diameter, row spacing, and interspacing of the boreholes, respectively. We found that (a) D/R has to be between 1:6 and 1:2; and (b) D/I has to be between 1:6 and 1:4, for sufficient depressurization in the surrounding rocks. The optimized borehole diameter and spacing parameters were applied in the field where the deformation of roadway was significantly reduced. Finally, we proposed a criterion to determine those parameters of depressurization boreholes for application in other geological and mining conditions.