Physical Model Experimental Study on the Coalface Overburden Movement Law on the End Slope of an Open-Pit Mine

Due to technological and safety limitations, there are considerable amounts of coal resources pressed under end slopes in open-pit coal mines. In recent years, this problem has gradually attracted the attention of researchers. How to realize the efficient recovery of side overburden resources while ensuring the stability and safety of slopes has become an important topic for the development of mining technology in China. A 2D/3D integrated simulation experimental device for end slope coal mining is developed. Based on the geological engineering conditions of the Ordos mining area in China, a typical geological engineering model of a near-horizontal slope condition is constructed to simulate the whole process of "roadway group formation-supporting coal pillar failure-slope rock mass instability". By tracking and monitoring the movement and failure processes of slope rock masses in an end-slope mining field, the yield failure characteristics of coal pillars and the movement and deformation laws of slope rock masses are revealed, and the deformation and failure zoning method of overburden rock in an end-slope mining field is proposed; in addition, the key stages, trigger conditions and key positions of slope deformation and instability are defined. The results show that under the coupling action of the "slope stress field" and "roadway group stress field", the actual stress of a supporting coal pillar in the deep part of a geometric centre along the slope of a roadway group is greater than the ultimate stress, and then large discontinuous deformations of multiple adjacent coal pillars around the central coal pillar are caused by compressive shear failure, which is the triggering condition of deformation and instability around the mining slope. The key position of yield failure of the supporting coal pillar is located in the deep part of the geometric centre along the slope of the roadway group. At the end of the mining adit, the supporting coal pillar within a width of 2.5-3 times the mining adit will not be destroyed. The boundary of the final collapse plane range of the roadway group is approximately a closed curve formed by two paraboloids, which are axisymmetric with the central pillar and open oppositely; the parabola opening in the shallow part of the slope area is small, and the parabola opening in the deep part of the slope area is large. There is a significant space-time correspondence between the failure of supporting coal pillars and the deformation of the slope surface. According to the failure process of the rock mass structure and the movement and deformation characteristics of the slope surface, the slope after failure can be divided into three areas, and the upper part of the slope is the key area of deformation and instability of the overlying rock mass in the end-slope mining field. These research results provide a theoretical basis for the scientific monitoring and stability control of slopes in an end-slope mining field.