Failure behavior and strength characteristics of coal-rock combined body under different confining pressures

A testing system MTS 815 was used to carry out triaxial compression test for Qianjiaying coal-rock combined body. The results show that the consolidation stage is shorter and it apparently has a linear elastic stage and a plastic yield stage under the influence of confining pressure. Ductility of post-peak stage is much more apparent with the in- crease of confining pressure. Based on the change laws of peak strain,elastic modulus,rupture angle and strength,the threshold confining pressure of deformation is 10-15 MPa. The failure mode of coal body is mainly shear failure,and some rock bodies have the same failure mode with coal body. The rupture angle is within the range of 14. 1°-38. 8°and its average value is 26. 84° which has little difference with 28. 31° calculated using Coulomb strength criterion. Residual strength has an increasing trend with the increase of confining pressure while rock Ds has the opposite trend. From 0 to 5 MPa,the decreasing range of Ds is the largest which reflects the sensibility to confining pressure. Then, with the increase of confining pressure,Ds shows a linear decrease. Finally,the values of m,s in Hoek-Brown and gen- eralized Hoek-Brown failure criterion are discussed.