Experimental study on fracture mode of lateral high and low thick and hard roof in mining roadway

The appearance of rock bursts in Shaanxi and Inner Mongolia area mostly occurs under the influence of secondary excavation disturbance. The breaking of the thick and hard rock structure above the coal seam induces the appearance of dynamic pressure near the working face and has become a major safety hazard in coal mine production. In order to clarify the impact of the breaking of the high and low thick hard rock layers overlying the mining roadway on the strength of the section coal pillars and the stability of the roadway surrounding rock and establish the mechanical model of the breaking structure of the high and low thick hard rock layers, and obtain the section coal pillars under the influence of the breaking disturbance structural deformation characteristics and stress distribution characteristics. The authors take the coal sample from the 11th panel of Bayangole Coal Mine as the research object, use a self-designed and processed high-level rock layer simulation loading device, and use the digital speckle correlation analysis method of the non-contact full-field strain measurement system, carry out the stress and deformation characteristics of the section coal pillars and low-level rock formations under the combination of different breaking positions of the high and low thick hard rock layers above the section coal pillars. The force characteristics and stress transfer mechanism of the coal pillars under the combination of different fracture positions of the overlying high and low thick hard rock layers are analyzed, and the mechanical models of the different fracture positions of the thick and hard roof on the upper part of the roadway and the overall instability load of the structure are established. The test results showed that the breaking of high and low thick and hard roof rock layers will cause stress concentration in the coal pillar goaf. The combination of different breaking positions of high and low thick and hard rock layers has a significant impact on the movement and deformation of the lower rock layers, the stress distribution of the section coal pillars, and the stability of the surrounding rock of the roadway. The overall structural stability of the coal pillar in the section is related to the location of the breaking point. The stress required for the failure of the coal body under the action of rotation is negatively related to the moment of the breaking point of the high-level rock roof on the top coal in the goaf. As the breaking point is farther away, the section coal pillar's force is gradually transformed from compression and shear to the compression and bending effect transmitted by the coal roof of the goaf. The relative position of the top slab breaking of the high and low thick hard rock layers affects the breaking of the low roof. When the low breaking point is within the high breaking point, the low roof will break once with the high roof. Otherwise, the low rock roof will rotate twice as the high rock breaks. Times broken. With the breaking of the high roof, the stress of the mining roadway and the overlying strata of the coal pillar is reduced, the stability of the coal pillar in the section decreases, and the risk of rock burst increases. The experimental research provides a reference for the prevention and control of dynamic disasters in mining roadways and the optimization of section coal pillar design under the conditions of deep thick and hard roof in Shaanxi and Inner Mongolia.