Mechanism And Control Of Deformation And Failure Of Roadway Along Gob In Mechanized Caving Face Of Extra Thick Coal Seam

The fully mechanized top coal caving mining in ultra-thick coal seams results in a large space and intense activity of the overlying strata,and the manifestation of mining pressure is particularly obvious.The small coal pillar roadway along the goaf has a high degree of surrounding rock fragmentation and severe deformation and damage after being subjected to multiple mining disturbances,which poses a challenge to the safe and efficient mining of the fully mechanized top coal caving face in ultra-thick coal seams.This article is based on the specific engineering geological conditions of the typical ultra-thick coal seam fully mechanized top coal caving face in Datong mining area,and adopts comprehensive research methods such as theoretical analysis,numerical simulation,and on-site testing to systematically carry out research on the spatial "double arch" structural characteristics of the overlying rock of the ultra-thick coal seam fully mechanized top coal caving face,the mechanism of the "double force source" action along the goaf roadway,and the mechanical behavior and control strategy of large deformation and failure.The main achievements are as follows:(1)The structural mechanics model of "stress arch fracture arch" in overburden space of fully mechanized top coal caving face in extra thick coal seam was established,and the expression equation of "double arch" geometric shape characteristics was derived.The correctness of the theoretical model was verified by combining the 3D discrete element numerical simulation results,and the influence rules of different main control factors such as coal seam thickness,coal seam elastic modulus,and basic roof thickness on the "double arch" structural mechanics characteristics were obtained.(2)A mechanical model of the "dual force source" action in the goaf roadway of the fully mechanized top coal caving face in ultra-thick coal seams was established.The characteristics of the I type,II type,and I+II type force sources in the surrounding rock of the roadway during goaf excavation and mining were analyzed,revealing the mechanism of large deformation and failure of the goaf roadway under the action of the "dual force sources".The sensitivity of different main control factors to the degree of deformation and failure of the surrounding rock of the goaf roadway was obtained through orthogonal numerical simulation experiments.(3)Based on the characteristics of "double arches" and "double force sources" in the fully mechanized top coal caving face of ultra-thick coal seams,a control strategy of "far field weakening-near field strengthening" in the goaf roadway is proposed.A calculation model for hydraulic roof weakening of large structures in the overlying rock space and anchor grouting strengthening of small structures in the surrounding rock of the goaf roadway is established,and the influence of different roof cutting positions and heights,as well as the strengthening rate of surrounding rock strength,on the stability of the goaf roadway is analyzed,The joint control parameters of "far field weakening-near field strengthening" have been optimized.(4)We conducted on-site tests and comprehensive monitoring of the surrounding rock control of small coal pillars along goaf tunnels in typical fully mechanized top coal caving face of ultra-thick coal seams,verified the correctness and rationality of the "double arch" and "double force source" theories,as well as the "far field weakeningnear field strengthening" joint control technology,and achieved the expected engineering application effect.This thesis has 60 figures,14 tables and 110 references.