Fracture development due to coal mining under unconformable overlying strata

Abstract：The development characteristics of fractures due to coal mining under deep unconformable overlying strata was investigated using the similar model test and DEM numerical simulation,and taking No.3 coal seam of Shizuishan in Ningxia Province as the engineering background.The comparison was performed between the results obtained from the similar model test and the DEM numerical simulation.It is realized that the development of fracture and the redistribution of stresses in overlying rock mass are both unique due to the unconformity between the coal strata and the overlying strata.It is found that the stress arch appears over the goaf in the overlying rock mass in the process of coal mining.The transmission of stresses is blocked by the unconformity of strata during the process of stresses redistribution induced by coal mining.That results in that the principle stresses concentrate at some local regions beneath the unconformity.The stresses concentration in these regions makes the failure of rock mass near the unconformity more intensive than that in other places.Finally,the saddle-shaped fractures zone which is high at left and low at right is formed over the goaf in the overlying coal strata.