Regenerative Roof Conditions In Slowly Inclined Coal Seams Roadway Rock Damage And Control

When the lower part of the very close coal seam group is mined,the roof plate of the upper mining area collapses and compacts to form a regenerated roof plate,whose structure has fracture characteristics and is highly susceptible to destabilization and fall under the influence of mining stress.This paper addresses the engineering problem that the stress environment and plastic zone of surrounding rocks in the lower back mining tunnel are changed after the formation of regenerated roof plate in slowly inclined coal seam,which leads to serious deformation of surrounding rocks and difficulties in support.The numerical simulation method based on double yield model is used to simulate the compaction process of the regenerated roof of the gently inclined coal seam and its stress distribution characteristics,analyze the stress distribution characteristics and the influence on the damage of the surrounding rock of the roadway during the transition from the primary roof stage to the regenerated roof stage,and compare the damage pattern of the surrounding rock of the roadway when the roadway is in the primary roof stage and the regenerated roof stage and the damage pattern of the surrounding rock of the roadway under the influence of superimposed mining action.The expansion characteristics of the plastic zone of the roadway surrounding rock under the influence of superimposed mining stress are compared,and finally the stability control scheme of the roadway surrounding rock is proposed.The main conclusions are as follows.(1)According to the numerical model calculation,after the compaction of the upper slowly inclined regenerated roof,the vertical stress of the slowly inclined regenerated roof as a whole shows the distribution characteristics of "O-ring" deviating from the center point of the mining area,the center point of the compaction area is shifted downward along the inclination direction,and the distance from the coal pillars on both sides of the mining area is not equal;the dynamic change of stress forms a stress concentration zone inside the regenerated roof and the The dynamic change of stress forms stress concentration zone,stress reduction zone and stress recovery zone inside and at the edge of the regenerated roof plate;the downward transfer of stress will significantly affect the stress distribution of the lower working face and the roadway,resulting in the phenomenon of stress increase and decrease in the back mining roadway.(2)According to the analysis of stress change in the back mining tunnel,the area with large stress fluctuation is concentrated in the transition area from the primary roof to the regenerated roof;in this area,the primary roof side is mainly affected by the support pressure at the edge of the upper mining area,resulting in a local stress increase;in the transition area,the regenerated roof side is mainly affected by the stress reduction of the upper regenerated roof,resulting in a stress reduction area in the roof of the lower back mining tunnel.The main stress of the roadway surrounding rock is reduced.(3)According to the distribution characteristics of the plastic zone of the surrounding rock of the retrieved roadway,the plastic zone of the surrounding rock of the roadway is expanded to a certain extent in the primary roof stage,influenced by the downward transmission of the support pressure at the edge of the upper mining area;in the regenerated roof stage,the damage of the surrounding rock of the retrieved roadway is mainly concentrated in the roof of the roadway due to the fracture structure characteristics of the regenerated roof itself;and under the action of the stress reduction zone in the regenerated roof stage,the plastic zone of the roadway The area of the plastic zone of the two helpers and the bottom slab is slightly reduced compared with the area of the plastic zone of the rock in the primary roof stage.(4)Under the influence of superimposed mining stress,due to the loose and fractured rocks in the regenerated roof and the poor stress conduction between the rock blocks,the change of the overrunning support pressure curve in the regenerated roof stage is smaller than that in the primary roof stage;by observing the expansion of the plastic zone of the surrounding rocks within 20 m in front of the mining work,it is concluded that the expansion of the plastic zone of the surrounding rocks under the influence of dynamic pressure in the regenerated roof stage is smaller than that in the primary roof stage.(5)In view of the fact that the damage of the surrounding rock in the retrieved roadway in the regenerated roof stage is mainly concentrated in the roof of the roadway,a full anchor cable support scheme is proposed for the roof,and the corresponding support parameters are given;through numerical simulation analysis of the supported roadway,the influence range of the stress field generated by the support body,the force of the support body,the position of the anchored section of the support body and the displacement amount after the support are obtained;after the later observation of the surrounding rock displacement,it is proved that According to the planning of the research system in this paper,the principle of controlling the surrounding rocks of the retrieval roadway under the condition of regenerated roof is established,which has certain guiding significance for the control of the surrounding rocks of such roadway.