Roof Fracture Structure And Roadside Supporting Mechanism For Gob-side Entry Retaining In Fully-mechanized Top-coal Caving Face Of Near Shallow Seam

The 4# coal seam in Awuzisu coal mine is thick or extra-thick with an average thickness of 8.22m and a depth of about 220m. The roof lithology above coal seam is soft, but the thickness of bedrock layer is large, which is near shallow coal seam. 4# coal seam is mined by fully mechanized caving mining method, and haulageway is preserved with gob side entry retaining. In order to maintain the stability of the surrounding rock of roadway, the requirements of the support mass along the gateway side should have sufficient strength. The strength of the filling body is related to the roof breakage and the stress environment. So,based on the exploitation of No.4 coal seam in Awuzisu coal mine,lateral roof breaking structure of shallow seam in Awuzisu coal mine on the gob-side entry retaining in the fully mechanized mining method and roadway support model were investigated by combination of theoretical analysis, similar material simulation, numerical simulation and field monitoring, and the main conclusions are as follows:(1) The evolution process of the fracture position and caving angle of the 4# coal seam was obtained by similar material simulation of gob-side entry retaining in fully mechanized caving mining in shallow coal seam according to the main physical and mechanical Awuzisu coal mine geological exploration data and 4# coal seam roof strata parameters.(2) The prototype of 4# coal mining in Awuzisu coal mine, the roof breaking structure of gob-side entry retaining in fully mechanized caving mining in shallow coal seam and the stress change of the support mass along the gateway side in the near shallow coal seam were simulated by using the UDEC numerical simulation software. The simulation of the similar material was carried out, and the whole process of roof movement in fully mechanized caving mining in shallow coal seam was analyzed. The support mass along the gateway side pressure in the rapid growth, and the growth rate gradually slowed down with the direct roof caving and the lateral direct roof restraint by goaf waste in the initial stage of the whole movement of the roof, the pressure in the support mass along the gateway side increases little and tends to be stable in the process of in the contact between main roof and gangue and the goaf was compacted gradually.(3) On the basis of similar material simulation and numerical calculation, lateral roof breaking structure evolution model of shallow seam in Awuzisu coal mine on the gob-side entry retaining in the fully mechanized mining method was built and the supporting resistance formula of support along the gateway side was deduced.(4) According to the geological conditions and mining parameters of 4-1101 working face in Awuzisu coal mine, maximum support resistance that the support mass along the gateway side needs for provision was calculated in process of mining, the optimal ratio of packing material combined with the pump ability and economy of packing material, the packing material with optimal ratio is applied to track crossheading of the 4-1101 working face, and the packing material was verified by deformation of the surrounding rock that monitored. The monitoring results show that the deformation of the roof and floor and the two side of the roadway is small, the control effect of surrounding rock deformation is better.