Synergistic Mechanism Of Co-mining Coal And Gas In Fracture Zone Of Overlying Strata In Coal Seam Group

After coal mining,the overlying strata fracture development,and a large number of pressure relief gas into the coal mining space.By studying the mutual influence mechanism between coal mining and the characteristics of fissure evolution of overburden strata and gas emission characteristics,reasonable gas drainage measures can be taken to solve the problem of gas over emission and realize the utilization of gas resources.In this paper,the synergistic mechanism of co-mining coal and gas have been studied by theoretical analysis,similar material test and numerical simulation.The main contents and conclusions are as follows:This paper clarified the connotation of synergistic mechanism of co-mining coal and gas.Taken coal mining,fissure evolution of overlying strata and gas emission as a unified system.Based on the progress of working face,the coverage area of overburden fracture and the gas emission quantity of pressure relief,the synergistic mechanism of co-mining coal and gas was established by using the synergetic theory prey model.Based on the 24208 working face of Shaqu Mine,the similar material test of fissure evolution of overburden rock have been carried out to study the evolution and deformation characteristics of overburden fissure in 3+4 coal mining.The tests indicated that there was a change of "micro-cracks-fissures extendingdevelopment of repose-micro fissure closed-generate new longitudinal micro-cracks" for longitudinal fissure cyclical evolution.Fissures height evolution ladder development of space research shows that the stope overlying strata separation porosity distribution curve was "M"type.According to the similarity test,the coal adsorption strain permeability model,coal rock deformation model and gas seepage coupling model were established.The above-mentioned models were used to simulate the deformation characteristics of overlying strata,the natural gas discharge characteristics of pressure relief gas and the technology of pressure relief gas drainage,and the results show that the cave rock have greater deformation,the floor have expansion deformation,and there was stress concentration up and down the coal face roof and floor;pressure relief gas flows along the fissures path to the goaf,the final pressure relief seam gas and fracture space gas to reach the equilibrium states;during the initial period of gas drainage,the quantity was larger,but decaied fast,after a period of time,maintained in a stable lower quantity.During the initial stage of drainage,the quantity increases with the negative pressure.The applied research of coal and gas co-mining mechanism were carried out,and the co-mining covariates were established by the actual conditions and similarity test of 24208 working face in Shaqu Mine.The research shows that when the advancement length Lm is constant,the synergetic coefficient k1、k2、k3 is a function of the change with S.By the variation law of S and k1,k2,k3 with the working face mining,the optimal placement layer of pressure relief drilling was determined,which was located near the inflection point of the curve.Through the analysis of the effect of pressure relief gas drainage,the quantity of the long directional borehole in the roof was 4 to 5 times higher than that in the unloading condition.In the early stage of high fissure,the gas drainage quantity and the concentration was high.After a period of time,the drainage quantity begin to decay,but the gas drainage purity was still higher than that of the coal seam;and the effect of the negative pressure was not always positively correlated with drainage.