Failure mechanisms and reinforcement support of soft rock roadway in deep extra-thick coal seam: A case study

The soft rock roadway in deep extra-thick coal seam is prone to large deformation disaster. In order to solve this problem effectively, taking the W3101 coalface of Xiao'kang coal mine as the engineering background, the failure mechanisms and the corresponding control technology were investigated by the methods of laboratory test, numerical simulation and field measurement. First, a series of tests were carried out on the basic mechanical properties of rock mass, in-situ stress and loose zone, and it was found that the failure mechanisms of soft rock roadway in deep extra-thick coal seam are poor lithology of surrounding rock, high in-situ stress, large loose circle and unreasonable original support. Then, based on the supporting mechanisms of grouting cable and concrete-filled steel tube (CFST) of bottom angle, a new collaborative reinforcement support (CRS) technology combining the two was proposed. Next, the numerical simulation shows that the CRS technology has good applicability in controlling large deformation of soft rock roadway in deep extra-thick coal seam. Finally, to exhibit the engineering application effect of the proposed CRS scheme, it was also applied in Xiao'kang coal mine. Comparing to the controlling effect of original support scheme, it can be seen that the average deformation of soft rock roadway reduces by 73.2 % under the proposed CRS scheme, and the steel arch frame of bottom angle is slightly deformed. Meanwhile, it is found that the grouts diffusion radius is nearly 1.21 m, and the deepest diffusion depth is 4.25 m, which also indicates again that the feasibility of the proposed CRS scheme in controlling large deformation of soft rock roadway in deep extra-thick coal seam.