Study on deformation characteristics of surface borehole in active coal mining area under repeated mining

In order to solve the problem that broken rate of the surface borehole is very high，which caused by overburden movement of the stope,especially the effect of repeated mining,based on the analysis of the characteristics of the overlying strata movement in the stope,the similar model is established on the basis of the engineering environment under the condition of Stratified Mining.Through stratified excavation and continuous monitoring of the effect of shear slip and separation of the overlying strata on the surface borehole monitoring line,the deformation characteristics of the surface borehole under the influence of mining are obtained.Under the influence of repeated mining,the ground surface boreholes in the mining area show the repeated moving characteristics of "increase→decrease→increase →decrease" and after sub level mining,the shear slip of the surface borehole increases by 30.12% compared with the upper layer mining;the deformation of the abscission layer show the characteristics of the continuous increase of "increase,increase,increase and increase" and after the sub level mining,the ratio of tensile deformation and the thickness of the surface borehole are increased by 29.8%.At the same time,the protection idea of surface borehole body reinforcement design is put forward.