Effect of Fracture Heterogeneity on Rock Mass Stability in a Highly Heterogeneous Underground Roadway

Rocks are a natural material with strong heterogeneity, and the heterogeneity affects the behavior and failure patterns of rocks and rock masses. Therefore, the factor of rock heterogeneity should not be neglected in cases of highly heterogeneous rock masses. In this study, the effect of heterogeneity on the rock mass stability in an underground coal mine roadway is investigated by introducing a stability analysis method that considers rock heterogeneity. The stability analysis method is combined with field investigation, laboratory testing, and numerical simulation. The rock mass heterogeneity is considered in the light of equivalent material properties, which are the heterogeneous rock mass properties weakened by heterogeneously distributed fractures. A Weibull distribution model is implemented into FLAC3D to characterize the rock mass heterogeneity. Sensitivity analyses regarding the rock mass properties and the mesh dependency are conducted to understand their effect on roadway deformation. A parametric study is performed to investigate the effect of the homogeneity index and other parameters that describe the rock mass fracturing intensity. The results show that the degree of rock mass heterogeneity has a significant effect on the roof deformation, failure extent, and other input parameters that describe the rock mass heterogeneity. The simulation results that are in good agreement with heterogeneity parameter data are estimated in the field. Thus, this method can be used as a back-analysis technique to obtain the homogeneity index and other input parameters through comparison to field deformation data, and can be applied to other engineering cases involving highly heterogeneous rock.