Mechanical mechanism of unconventional asymmetric failure in mining roadways: A joint research on crack propagation and engineering fracture

It is of great significance to study the failure mode of mining roadways for safe coal mining. The unconventional asymmetric failure (UAF) phenomenon was discovered in the 9106 ventilation roadway of Wangzhuang coal mine in Shanxi Province. The main manifestation is that the deformation of the roadway on the coal side is much greater than that on the coal pillar side. A comprehensive study was conducted on on-site detection, theoretical analysis, laboratory tests and numerical simulation of the UAF phenomenon. On-site detection shows that the deformation of the coal sidewall can reach 50–80 cm, and the failure zone depth can reach 3 m. The deformation and fracture depth on the coal pillar side are much smaller than those on the coal side. A calculation model for the principal stress of surrounding rock when the axial direction of the roadway is inconsistent with the in-situ stress field was established. The distribution of the failure zone on both sides of the roadway has been defined by the combined mining induced stress. The true triaxial test studied the mechanical mechanism of rock mass fracture and crack propagation on both sides of the roadway. The research results indicate that the axial direction, stress field distribution, and mining induced stress field distribution of the roadway jointly affect the asymmetric failure mode of the roadway. The angle between the axis direction of the roadway and the maximum horizontal stress field leads to uneven distribution of the principal stress field on both sides. The differential distribution of mining induced stress exacerbates the asymmetric distribution of principal stress in the surrounding rock. The uneven stress distribution on both sides of the roadway is the main cause of UAF formation. The research results can provide mechanical explanations and theoretical support for the control of surrounding rock in roadways with similar failure characteristics.