Mechanism of fault activation when mining on hanging-wall and foot-wall

When fault exists in overburden strata,the earth-surface subsidence laws would be greatly different from the laws without faults. To study the mechanism of fault activation when mining on hanging-wall and foot-wall,the fault ac- tivation mechanical criterions were built. At the same time,the activation difficulty of mining on hanging-wall and foot- wall was analyzed by numerical simulation and analogue modeling. The results showed that the stability condition of footwall mining is more severe and fault can be activated more easily when mining on footwall. This is because the sta- bility needs not only to meet the requirement that the fault zone rock mass does not slip at the fault plane,but also meet the requirement that the fault plane does not produce separation. For hanging-wall mining,with the advance of the working face,the normal stress of the rock mass in the shallow fault zone gradually decreases and the shear stress gradu- ally increases,while both the shear stress and normal stress of the rock mass in the deep fault zone gradually increases,and the rock mass in the shallow fault zone is activated ahead of the rock mass in the deep fault zone. In the advance of working face,the ratio of shear stress to normal stress of rock mass in footwall mining is 3-5 times of that in hanging-wall mining. Fault is activated when mining on footwall,only slight cracks occur on the surface of fault outcrop,and no obvi- ous steps are formed. However,fault outcrop will produce obvious steps sinking when mining on foot-wall.