In-situ disturbed mechanical behavior of deep coal rock

Deep mining is the main way to obtain mineral resources in China. However,the engineering practice of deep resource mining is advanced ahead of the theory research,which usually results in frequent disasters. Systematic exploration of in-situ mechanical behavior of deep rock mass has become a basic scientific problem to be tackled in the field of deep mineral resources high-efficiency mining. For the deep coal mining,through capturing the stress path of the deep rock from underground measured data,the experiments of in-situ rock mechanics and failure characteristics of deep coal were conducted under the mining-induced stress path and the deep in-situ environment factors in consideration. The main conclusions are shown as follows:① the depth is an important factor affecting the mechanical characteristics of deep in-situ rock mass. The strength of rock mass increases nonlinearly with the depth. The strength of shallow (with low confining pressure) rock mass is less affected by the loading rate,and there is a sensitive range for loadingunloading rate. ② Engineering disturbance is another important factor affecting the mechanical properties of deep insitu rock. The strength of rock mass under the mining-induced stress path is lower than that of conventional triaxial test. The volume expansion for specimen under low confining pressure and the volume compression for specimen under high confining pressure are different from that of conventional triaxial test. ③ For the in-situ stress path and the increase of depth,the number of the microcracks on the surface of the specimen decreases after failure,and the “half Y”tensile-shear failure changes to “half X” pure shear failure. ④ The proposed in-situ rock mechanics test method can simulate the real three-dimension stress state caused by the underground engineering activities,and can effectively reveal the mechanical characteristics of coal and rock in the disturbed environment of deep mining in the laboratory.