| After years of practice and exploration, double U-type ventilation has been adopted to the fully mechanized caving working face with high gas in Lu’an Mining District. However, with the production unceasing and the mining speed accelerating, fully mechanized caving face was characteristiced with a large quantity of gas emission and high intensity, uneven emission, which brings new challenges for the gas control management. Based on these, Y-type ventilation was proposed instead of the original double U-type ventilation, which conveying roadway and air-in roadway are the first air-in entry, and air-return roadway is the second air-in entry. But whatever the original double U-type ventilation or Y-type ventilation, a certain section roadway should retanined to meet ventilation requirements and gas control, which is gob-side entry retaining. Wood crib were previously used for retaining roadway, whose disadvantages include goaf ventilating, great consumption of wood, small section of roadway retanined, big labor intensity, big auxiliary transport workload, construction slow, and poor gas control. This paper proposed a new method for gob-side entry retaining with high-water material to ensure the surrounding rock stablity of gob-side entry retaining and the reliability of gas emissions. However, mining influence of fully mechanized top coal caving working face is heavy for its strong mining and the section of gob-side entry retaining is great. The stability control of surrounding rock for gob-side entry retaining requires futher research to provide reasonable surrounding rock control technology.Based on the practice of gob-side entry retaining of N2105 fully mechanized top coal caving working face with high water material, methods of engineering practice, laboratory experiment, numerical methods and field trials have been used, mechanical model between the roof(top coal) and the roadside filling body based on the roof breakage characteristic of GER-FMTCC, the capacity of transmiting and carrying of top coal in GER-FMTCC is analyzed, stability control mechanism of top coal in GER-FMTCC is revealed, stability control technology for large deformation of surrounding rock is proposed, a Y-type ventilation is put forward and its primary and secondary air distribution ratio is determined, and gas migration law and its drainage effect under different drainage conditions is obtained. The following conclusions include:(1) By analyzing roof lateral breaking features of GER-FMTCC and the implementation conditions of gob-side entry retaining, top coal and the immediate roof will be firstly cut outside of the roadside filling body, and then the main roof will be cut outside of the roadside filling body under the effect of overburden and the roadside filling body; mechanical model between the roof(top coal) and the roadside filling body is established and the calculation formula are obtained; combined geological conditions of N2105 fully mechanized top coal caving working face in Lu’an Ltd of Shanxi Province, cutting resistance of the main roof and the immediate roof are obtained, and the cutting resistance of the main roof is greater than the cutting resistance of the immediate roof.(2) Roadside support system mechanics model in GER-FMTCC is established, and calculation formula of transmiting capacity of top coal is obtained; the calculation result shows that with the increase of top coal stiffness, the stiffness of roadside support system increases and the transmiting capacity of top coal increase.(3) The top coal can be divided into plastic zone and slip zone, thus mechanics model of top coal carrying capacity in GER-FMTCC is established, and calculation formula of carrying capacity of top coal is obtained. The calculation result shows that with the increase of top coal lateral force from the goaf, the carrying capacity of top coal increase; with the increase of top coal lateral force from the solid coal rib, the carrying capacity of top coal increase; with the increase of top coal uniaxial compressive strength, slip plane and perpendicular to the direction of inclination α(top coal breaking angle) is smaller and the carrying capacity of top coal increase; with the increase of plastic zone top coal confining pressure coefficient, the carrying capacity of top coal increase; with the decrease of the upper and lower surfaces shear stress of top coal, the carrying capacity of top coal increase.(4) The stability evolution law of top coal above roadside the filling body is analyzed, the deformation and vertical stress evolution law of top coal above roadside the filling body is obtained. The result shows that with the increaseof the top coal thickness, or the decrease of the top coal elastic modulus, or the dercrease of the immediate roof thickness, or the increase of the main roof elastic modulus, the sinking deformation of top coal increases; with the increaseof the top coal thickness, or the decrease of the top coal elastic modulus, or the dercrease of the immediate roof thickness, or the decrease of the main roof elastic modulus, the vertical stress of top coal decreases; with the increase of roadway width, or the increase of roadside filling body width, the sinking deformation of top coal increases and the vertical stress of top coal decreases andthen increase.(5) Large deformation control principles of GER-FMTCC are proposed, which includes increasing the support strength of solid coal rib, reinforcing the roof(coal) of roadway, building the roadside filling body with early strength and speedy increase resistance, reinforcing the top coal above the roadside filling body, raising the confining pressure of top coal.(6) The influence factors and law of large deformation of surrounding rock in GER-FMTCC are researched, and the influence law of the stability of surrounding rock in GER-FMTCC from the strength of surrounding rock and the roadway width are obtained; deformation of roadway surrounding rock can decrease by raising the toof and the solid coal rib strength, but the deformation of backfill will increase while the strength of backfill also increases; with the increase of roadway width, the deformation of surrounding rock increases, especially the deformation of roof and floor.(7) The roadside technology and its parameters of GER-FMTCC are researched, and the influence law upon the surrounding rock stability of the roadside filling body width and its strength.(8) The surrounding rock control principle of "controlling roof and strengthen rib" is proposed. It is the technology of roof high prestressed bolt support, diagonal anchor cable support and solid coal rib high prestressed yielding bolt support; the support technology and its parameters of gob-side entry retaining of N2105 air–return roadway are researched by numerical calculation.(9) The control technology and parameters of top coal in GER-FMTCC is researched by establishing numerical model in UDEC. The top coal is divided into three regions which including separating region above backfill, tension of region above gob-side entry and shear failure region above solid coal. These regions are the key parts to control surrounding rock. The technology of high prestressed anchor cable support timely, high-water material filling backfill to support roof timely, anchor cable support beside goaf, reasonable length of backfill and advancing support under pressure are proposed, and these parameters are determined.(10) In three kinds conditions of main and auxiliary lane with different wind, the gas distribution of working face and goaf, the pressure at both ends of the face, air leakage of face, wind distribution of upper-corner were analyzed and compared. When wind distribution of haulage gateway and return-air gateway is 3: 1(the wind amount of haulage gateway is 2700m3 and the wind amount of return-air gateway is 900m3), the gob gas exploses in least way, gas flows into face is smallest, eddy zone in upper-corner is smallest, the pressure at both ends of the face is maximum, effects of face ventilation and gas treatment are the best.(11) Vertical height of ground drilling hole is determined as 22 m, it is 40 meters away from return-air gateway based on mining crack "O" theory. Drilling hole in fracture zone and kilometers hole are arranged also based on mining crack "O" ring theory. Combined with the layout of drilling hole in fracture zone, its final position should be optimized for 26 meters above t the seam floor and 40 meters away from return-air gateway.(12) According to N2105 gas distribution of fully mechanized caving face,it has a high gas-rich region beside return-air gateway 120 meters in goaf. Gas will flow into the face and gob-side entry as the wind flows. Drainage pipe not only pumps gas close to face in the range of 20 ~ 50 meters, but also need to increase the stability of pumping deep area 120 meters inside goaf. The gas of goaf and working face should be controlled in nature.(13) The research has applied to gob-side entry of N2105 fully mechanized top coal caving working face successfully. The deformation of surrounding rock is controlled effectively to meet the demand for gas treatment. The gas drainage works well and it has made significant technological economic and social benefits. |
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