RESEARCH ON MINING RESPONSE CHARACTER OF UNDERGROUND SURROUNDING ROCK AND OVERLYING STRATA TRANSITION FROM OPEN PIT TO UNDERGROUND MINING

Based on the engineering background of Jingning phosphate mine of Yunnan Phosphate Chemical Group Co.,LTD.,the displacement and stress response characteristics and dynamical evolution process of underground surrounding rock and overlying strata were studied after transformation from open-pit to underground mining of room and pillar method. And we carried similar material simulating experiment and digital photographic measurement technology to do target researching on these issues under the condition of two different ore body dips of twenty degrees and fifty degrees. The results showed that:(1) The evolution process of mining deformation of underground surrounding rock and overlying strata could be divided into three stages, which contained the stage of small deformation in originally small and local scale, linear continuous increase stage and the whole nonlinear violent collapse stage. (2)With the ore body dip increasing from twenty degrees to fifty degrees, the mining influence area narrowed down in a small range, the deformation slowed down of underground surrounding rock and overlying strata, and the geometric shape of settlement curve changed from asymmetric channel type to asymmetric bowl shape. (3) The abrupt occurrence of instability of underground surrounding rock occurred in the process of ore pillar recovery, and it presents the obvious The Domino Effect. The conclusions provide a theoretical reference for ground pressure management and slope maintenance in mine transition from open pit to underground mining.