Study On The Development Law Of Repeated Mining Induced Water-conducted Fissures And Mining Upper Limit Under The Condition Of Soft Rock Roof

With the continuous consumption of coal in the shallower part of the eastern mining area in China,more and more coal mining conditions become more complex,especially in the eastern mining area,the main problems faced by the mining of coal resources in the eastern mining area in recent years are to continue to mining to the deep,mining under various water bodies(including loose layers)and mining under buildings.In this paper,the complex hydrogeological structure conditions under the sea are taken as the research background,and the core key issue is the repeated mining and superimposed failure of the weak roof.The structural conditions of the water-bearing layer of the soft rock roof in the sea area,the seawater and the water content under the Quaternary Based on the systematic study of the seepage interface,multiple methods such as formula calculation,simulated mining,measurement comparison and other methods are used to study the superimposed failure of the weak overburden rock during repeated upward mining.The main conclusions are as follows:(1)The structural characteristics of the quaternary loose layer(thickness about 90m)"composite water-resisting layer" in the sea area are determined by using the existing exploration data and related theoretical analysis;Using chemical element analysis and borehole observation methods,the difference between seawater quality,head and shallow groundwater is studied,and it is determined that the infiltration interface of sea water in the study area is quaternary "one partition",and the infiltration interface of quaternary "lower bearing" is base rock weathering-oxidation zone water barrier Judging the mining grade of the water body in the working face of the study area is grade I from the angle of partial safety.(2)Through the finite element numerical simulation,the destruction effect of overlying mining on the soft roof is studied.At the same time,the indoor simulation of similar materials is repeated once,and the maximum height of the water flow fissure zone on both sides of the upper goaf is 55 m,which enters into mudstone and calcareous mudstone formation,the basic characteristics of the development of the "Terrace"-type water-conducting fracture zone will be formed.If the parallel distance between the two coal seams is greater than the critical damage value of 12 M,there is no need to consider the superimposed effect of overburden damage when repeating mining from bottom to top.(3)On the basis of the above research results,based on the basic principle of not affecting the "lower" of the Quaternary system,the size of the waterproof coal pillars in the normal part of the H1105 working face is 67 m,and the size of the waterproof coal pillars at the fault is 78 m.It is comprehensively determined to be-168 m,and the thickness of the bedrock and the thickness of the protective layer meet the requirements for the retention of waterproof coal and rock pillars within the working face.Finally,combined with the geological and hydrogeological structural characteristics of H1105 working face,the feasibility and safety of upward mining are comprehensively evaluated.The research area has the basic hydrogeological conditions for safe mining under the above-mentioned designed mining upper limit conditions.The research results of the thesis have important practical value for the evolution of groundwater flow field,the analysis of infiltration interface,the study of the law of overburden failure and the comprehensive determination of the mining upper limit under the condition of repeated mining under soft rock roof.The paper has 88 pictures,30 tables,and 101 references.