| In recent years,with the increasing modernization and efficiency of China's coal mine construction,the problem of mining replacement tension has become increasingly prominent,which makes the gob-side entry retaining technology with small pillar loss and less roadway excavation frequently used in the alternating arrangement of working face in major coal mines.In this paper,by means of field investigation and analysis,theoretical analysis,numerical simulation,laboratory test and industrial test,aiming at the stability control of surrounding rock of gob-side retaining roadway filled with concrete material in fully mechanized caving face of Gaohe Coal Mine and Changcun Coal Mine in Luan Mining Area,the basic roof-side fracture location is calculated to provide the overburden structure type of gob-side retaining roadway and the bearing structure of gob-side retaining roadway.According to the interaction between overburden structure and internal bearing structure and the calculation of bearing capacity of components of internal bearing structure,it provides guidance for the stability control of surrounding rock in gob-side retaining roadway.On this basis,aiming at the problems of low early strength and high cost of roadside filling material,a new roadside filling material was developed in combination with coal-based oil slag of Luan Group,which can effectively improve roadway stability.The early strength of side filling material reduces the material cost.The above research results have been successfully applied to the gob-side entry retaining engineering of W1319 and E1303 working faces in Gaohe Mine.The main achievements of this paper are as follows:(1)The failure characteristics of filling body of high aspect ratio concrete gob-side retaining roadway in Luan Group are investigated,and five failure modes of filling body beside roadway are counted: slight breakage of upper and middle parts,severe breakage of upper and middle parts,through cracks,serious breakage,inclination instability of filling body and lower breakage.The main failure modes are found to be the second and third failure modes.The causes of deformation and failure of filling body beside roadway are analyzed.Through the field measurement data,it is found that there is a strong correlation between the filling state of roadside and the surrounding rock stability of gob-side retaining roadway.(2)The UDEC numerical model was established to study the influence of fracture location on the stability of surrounding rock of gob-side retaining roadway,and a mechanical model of internal bearing structure was put forward to calculate the load of bearing structure in gob-side retaining roadway stage and secondary mining stage.The fracture location of basic roof was analyzed,which was beyond the anchorage strengthening area,located in the anchorage strengthening area and located in the nonuniform pressure.The loads borne by the filling body of five internal bearing structures,namely,belt shrinkage,above the filling body of roadway or roadside and outside the filling body of roadside.(3)In order to determine the bearing structure form in gob-side retaining roadway,a lateral fracture mechanics model of basic roof of gob-side retaining roadway is established,and the fracture location of basic roof is solved.The effects of elastic foundation coefficient,elastic modulus of basic roof,load concentration and width of filling body near roadway,and fracture span of basic roof on the fracture location of basic roof are explored.(4)Axial compressive strength is proposed as the strength index of the filling body beside the roadway with large aspect ratio;PFC meso-numerical model is established to study the size effect of the filling body beside the roadway,and the correction coefficient of the strength size effect of the filling body beside the roadway is obtained by fitting;the strength variation characteristics and mechanism of the filling body beside the roadway with large height-width ratio are studied under the condition of water immersion along the goaf.Compared with the formula for calculating the bearing capacity of filling body near concrete roadway,it guides the stability analysis and control of surrounding rock of gob-side retaining roadway.(5)In view of the problems of insufficient early strength and high cost of roadside filling materials which have not been solved by previous studies,and combined with the solid waste treatment of coal-fired oil slag in Luan Group,a new type of concrete material and special admixture have been developed.The new type of concrete material meets the requirements of slump,initial setting time,early strength and final strength of roadside filling materials along goaf retaining roadway,and solves the problems of concrete slump,initial setting time,early strength and final strength.The problems of low early strength and high cost of materials are studied.The conversion coefficient of axial compressive strength and cubic compressive strength,size effect and strength weakening effect of new roadside filling materials under water immersion environment are studied.The new roadside filling materials show smaller size effect and stronger resistance to erosion.Regular numerical simulation method of gob-side entry retaining is established,and numerical model is established to compare and analyze the effect of gob-side entry retaining with constant strength conventional material,low strength conventional material,conventional material and new material.The numerical simulation results show that the new material can effectively reduce the deformation of gob-side retaining roadway,and is more conducive to the stability of surrounding rock of gob-side retaining roadway than the conventional material filling.(6)Some of the above research results have been successfully applied to gob-side entry retaining in W1319 non-pillar working face and E1303 working face of Gaohe Coal Mine,and good engineering results have been achieved. |
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