Study On Technology Of Gob-side Entry Retaining Without Ribside Support In 3.2m Mining Height

Gob side entry retaining is an important leap in coal mine production technology.It is one of the hotspots in mining engineering research in recent years.The gob side entry retaining without ribside support under the condition of natural caving,no need to take the initiative to cut the top,is of low cost and simple process among many branches of gob side entry retaining.In recent years,it has been successfully applied and achieved good economic benefits in the La omupo coal mine and the Orchid baoxing coal mine.However,in these cases cutting heights were below 2 m.In order to achieve the breakthroughs of gob side entry retaining under the conditions of medium thick and thick coal seam,in this paper study is based on the 11#coal seam with the cutting height of 3.2 m in the Ji`anda coal mine.This thesis generate required overburden rock conditions of gob side entry retaining without ribside support though study on rupture regularity of overburden rock.Through the superposition continuous plate mechanics model and the immediate roo f thickness theory,the supporting strength of the coal seam roadway in the 11#coal seam and the surrounding rock control parameters of the corresponding typical layered roof are obtained.Numerical simulation is used to verify the theoretical analysis.The main research results are as follows.(1)Through theory analysis,suitable roof type to apply gob side entry retaining without ribside support is realized.In particular,the immediate roof should be amedium stable or unstable rock stratum,which can be cut off along the side of the roadway and the total deformation of the lower rock stratum under the stress of the key block is predictable and not too large.The significance of roadway support to roof activity is that,when the roof rock layer is caving,the stiffness coefficient of the cushion is raised through the characteristics of fast increasing resistance and support stiffness of the support in the roadway,forcing the controllable thin layer rock to break in the outside of the roadway and slowing down the inclination of the rotary sinking of the thick strata.In the process,the suitable surrounding rock structure is formed.To face the inability of the roof rock strata to pressure,support needs a certain amount of shrinkage.Under the premise of the auxiliary support itself is not damaged,the settlement of the lower roof is prevented as far as possible,and the surrounding rock control techniques such as anchor cable support or shelf support are combined to form a stable small structure with surrounding rock.(2)By using the superimposed continuous laminates model and the load strip division method,the roof collapse mechanics model is established.The role of supporting resistance in roadway is introduced,and the early cutting resistance formula for passive side cutting of gob side entry retaining without ribside support is summarized as follows:(?)The critical support strength of the later control roof is as follows:(?)(3)Through theoretical analysis,the problems when faced with large mining height were summarized,the rock mass index was introduced to evaluate the roof rock collapse characteristics.The immediate roof thickness formula for different quality rock layers was generated,thus the theoretical increment value of the support resistance in the roadway under increasing mining height was derived,which is exploration and paving way for gob side entry retaining without ribside support under large mining height.(4)Based on the simulation which geological conditions of the Ji`anda 11#coal seam were referenced as simulation parameters,it is shown that the immediate roof rock collapse in the 11#gob is divided into two groups.The first group of lower sandstone mudstones,with a total thickness of 1.8m,and a lateral suspended length of15~20m,and the second group consist of Medium sandstone,siltstone,10#coal and mudstone which are caving at the same time,have a total thickness of 8.5m,lateral suspended length is 20~30m.The collapse of siltstone in the main roof occurred when cutting length is about 50m.The the auxiliary supporting strength should be designed above 900~1200k N/m in the roadway of 11#coal seam in the Ji`andan mine.It is estimated that the roof subsidence is within 338mm and the side deformation is within254mm.Since the 110102 working face in the north wing of the Ji`andan 11#coal seam is being excavated,the replacement 110103 working face mining roadway has been drifting and the work facing is beside the mine boundary,so the industrial test has not been carried out at the 11#coal seam.The research can be applied to the 110106 mining face in future and the medium thick and thick coal seams with the similiar geological conditions but need to increase economic benefits.