Complex geological condition and different mining methods in coal mining will result in multi boundary condition of roof.Under different boundaries,limit load and broken pace of hard roof was different without fail.5 roof mechanics models with 5 different boundary conditions were set up.Roof limit load under different boundaries(4 sides fixed,3 sides fixed and 1 side simply supported,adjacent fixed and adjacent simply supported,opposite side fixed,3 sides simply supported and 1side fixed.) was obtained by plastic limit method.Variation rule of limit load with k(ratio of advance distance to mining face length) was analyzed.Roof limit load reached maximum under the condition of opposite side fixed and opposite side simply supported boundary.4 sides fixed boundary was secondary.Other 3 boundary conditions were almost equal.Minimum roof broken pace of every boundary condition was obtained on the basis of roof limit load,which was verified by numerical simulation.
In this paper,to research the stability of overlying water-resistant strata and prevent the roof water inrush accidents as well as implement water-preserved-mining,we regarded the water-resistant strata composed by only one rock stratum as clamped rectangular thick plate on foundation,and took the support effect of broken rock mass under the water-resistant strata into account,then deduced the deflection and stress expression according to energy method,and obtained the stress distribution characteristics of overlying water-resistant strata,as well as the variation rule of critical load along with working face advancement.In addition,combined with specific engineering practice,the stability of overlying water-resistant strata was analyzed by numerical simulation.The results indicate that: 1) after coal seam mining,the stress of overlying strata reaches the maximum value in the middle of longer boundary of the plate,where the rock is easy to be damaged;2) the supporting effect of broken rock mass have important influence on the stability of overlying water-resistant strata,that is,the thinner the mining thickness is,the stronger the supporting effect of broken rock mass to the overlying water-resistant strata is,and the more difficult the water-resistant strata to be broken.The research results can provide some reference for the prevention of roof water inrush and water-preserved-mining practice.
The mining with water resources protection in arid and semi-arid mining areas is not only an important national development strategy,but also one of the key study contents in the basic and applied sciences.Combining with the specific geological and mining conditions in Shendong coal mine,some researches on basic theory of mining with water resources protection and their application to arid and semi-arid mining areas are performed systematicallyi,ncluding the analysis of hydrogeological structuret,he development law of water flowing fractured zone in overburden rockt,he stability of the water-resisting key stratat,he water-preserved mining method with the aquifer above the water-resisting strata,the advance dewatering,transferring and storage of the water for the aquifer above the non-water-resisting strata,etc..According to the analysis of hydrogeological conditions,the shallow water-bearing region is classified into four types of hydrogeological structure;and the water-resisting strata area is classified into five water-bearing structures,so five kinds of regionalizations in water-preserved mining are put forward.According to the field measurementt,he numerical simulation and the theoretical analysis,the crack evolution law of mining strata and the seepage passage development law are revealed;and then the instability(destabilization) condition of the water-resisting key strata is given.Considering the various geological and mining conditions,aiming at the aquifer above the water-resisting strata,some water-preserved mining methods are proposed,such as the water-preserved mining by controlling the structural stability of the water-resisting key strata,the water-preserved mining by controlling the close of the mining water-conduct crack,and the water-preserved mining by filling in partial support area.Aiming at the aquifer above the non-water-resisting strata,the storage method of transferring water from the aquifer to goaf by advanced dewatering is put forward,which has a good application effect in practice.
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