Experimental Study On The Movement Law Of Overlying Strata And Surface Caused By Instability Of Strip Coal Pillar

Strip mining is widely used in China.In order to protect the surface buildings and maximize the recovery of coal resources,a lot of strip coal pillars and unfilled goaf are left behind in the strip mining area.The strip coal pillar bears the overburden load for a long time,and the possibility of instability is greatly increased by the influence of the water accumulation in the goaf,the adjacent mining activities and the new construction of the construction of the ground.The instability of strip coal pillar leads to the secondary movement of overlying strata and the surface,which is a potential hazard of surface disaster.However,the Iaws and characteristics of the overlying rock and surface movement caused by the instability of the strip coal pillar are not clear,so it is impossible to take scientific and reasonable preventive measures.Therefore,it is necessary to carry out research on this.Based on the achievements of previous studies on the stability of the strip coal pillar,the mechanical system of the pillar-roof and the theory of surface subsidence in strip mining,the law of the overlying and surface movement caused by the instability of the strip coal pillar is studied by the combination of physical simulation and numerical simulation on the premise of the instability of the strip coal pillar.The main work of this paper is as follows:(1)A similar simulation material containing paraffin wax was used to prefabricate the coal pillar model,and the model was heated by electric heating wire to achieve the instability of the strip coal pillar model.The uniaxial compression tests of paraffin-containing materials with different ratios showed that the strength of the strip coal pillar model increased with the increase of the paraffin content;When the ratio 1s constant,the strength discreteness of the model specimen is small.(2)A three-dimensional integrated simulation test system with flexible loading device has been developed,which has the advantages of simple structure,convenient assembly and disassembly and stable performance,which improves the efficiency and accuracy of the three-dimensional simulation test.Combined with the advantages of two-dimensional and three-dimensional physical simulation tests,the deformation laws of overlying strata and ground surface and the evolution law of overburden stress field are studied.The results show that the instability of the strip coal pillar leads to more significant overlying strata movement than the strip mining,and its influence on the deformation of the overlying rock and the surface deformation is greater than that of the stress,and the vertical stress of the pillar after the instability is greater than that before the instability.(3)The results of the physical simulation test are verified and further analyzed with the FLAC3D numerical simulation software.The results confirm the correctness of the physical simulation test.At the same time,it shows that the vertical stress of the roof of the coal pillar is changed from double peak to a single peak after the instability of the strip coal pillar,and the peak is increased by 2.65MPa before the instability,and the surface subsidence and horizontal movement all increase greatly,These displacements will damage the surface structures.