Study On The Technology Of Gob-side Entry Retaining With Longwall Top Coal Caving System And Its Application In Lu'an Mining District

As increasing of mining depth, advancing of outputs of a single working face and changing of geological conditions, the disallowed gas concentration appears frequently at longwall top coal caving face in Lu'an mining district, blocks the farther advancing of producing level. Based on the investigation about the approaches of gas control, this paper puts forward gob-side entry retaining technology with large and small section to change dissolute direction at longwall top coal caving face, prevent appearance of disallowed gas concentration radically, and realize intensive and high efficiency mining under the conditions of special coal seam. According to the mining conditions in Lu'an mining district, this paper study the rock strata controlling theory, stability of surrounding rock, roadway supporting technology and rules of phenomenon of underground pressure on gob-side entry retaining at longwall top coal caving face by compensative ways of theory analysis, similar simulation and 3-demension dynamic numerical simulation. This paper has setup the base for application of technology of gob-side entry retaining at longwall top coal caving face.This paper analyzed stability of surrounding rock influenced by gob-side entry retaining under different conditions and brings forward supporting inner and gob-side rules of entry by using 3-demension dynamic numerical simulation and similar simulation. According to analysis of collapse characters of roadway supporting by bolting and meshing or cable anchor and basic break rules of main roof ,this paper put forward the conception of large and small structure under the condition of gob-side entry retaining at longwall top coal caving face. Based on the stability analysis of key-block with large structure, the feasibility of gob-side entry retaining has been demonstrated. Through practical tests about rules of phenomenon of underground pressure influenced by gob-side entry retaining with large and small section, the relations of roof movements with top-coal broken and dropped are found: the convergence of roof appears mostly between 2 meters ahead of the working face and 15 or 20 meters behind the working face, and become to stability from 20 to 40 meters behind working face. Practices of gob-side entry retaining with large section at Changcun coal and with small section at Wangzhuang coal show that application of gob-side entry retaining with Y or J ventilation system can solve the problem of disallowedgas concentrations at high gassy longwall top coal caving face .With theory analysis, experiment research and spot test, this paper takes the lead in establishing technology system of gob-side entry retaining with large section or small one. According to rules of timbering economically, creatively utilized forming trigon "dismissing stress" or "low stress" zone in caved bolting and meshing entry, gob-side entry with small section is retained. Through pre-tensioned cable anchor with high strength, bolting and meshing support with high strength and filling with high-water material to increase supporting ability of top-coal, roof and coal wall, gob-side entry with large section is retained at longwall top coal caving face. Based on the successful application of gob-side entry retaining at longwall top coal caving face, a new way for realizing intensive and high efficiency is put forward in thick seams.