Impacts Of Different Material Compositions On The Permeability Of Fractured Fault Zone In Coal Measures

Permeability of fractured zone in fault determines the hydraulic conductivity and capability of inducing water inrush accidents of faults.Material composition and interal structure determine the permeability of fractured zone in fault.Filling materials in the fault collapse from surrounding stratum with different lithology,as a result that internal fracutres distribution,shape,particle size and chemical composition of fractured rocks are different.In this paper,theoretical analysis,laboratory tests and field engineering examples are used to investigate the impacts from material composition on permeability of fractured zone in fault,and some results have been concluded as following:(1)From different observation scales,taking F2 fault in the Renlou coalmine and DF200 fault in the Qianyingzi coalmine of Anhui province as examples,different zone properties and material composition in fault are investigated.From macro-perspective,it is found that material feature including the fracture feature,filling and cemented feature,fissure density and permeability in fault vary with the distance to fault surface.The results of durability test show that fractured rocks in water after 30 days can be disintegrated into three types,including intacted,cracked and muddy types with different particle size distribution.In the fractured rocks in the fault of coal measures,there can be found considerable clay minerals.The micro-pores and micro-fissures in the clay mineral mass determine the disintegration type of fractured rocks.(2)Twice laboratory crack tests are carried out to investigate the fractured feature and particle size distribution of different lithology rocks.In the tests,fracture loss rate of mudstone is calculated more than that of sandstone and limestone.However,fractured degree of mudstone is weaker than that of sandstone and limestone.Particle size distributions of different lithology cracked rocks are different that cataclasite(?20mm)content of mudstone is more than that of sandstone and limestone.(3)Laboratory seepage tests are designed to investigate the impacts from particle size and clay mineral content on the permeability of fractured rocks.The results reveal that the content of small particle with a diameter of less than 1mm determines the evolution of porosity,permeability coefficient and hydraulic gradient.And permeability of fractured rocks is determined by their particle size distributions.When porosity set as a constant,their permeability coefficient increase with content of big size particles.And serious expansibility of clay mineral can weaken the permeability of fractured rocks.(4)Theoretical analysis and formula derivation explain impacts from particle size and clay mineral content on the permeability of fractured rocks in fault of coal measures.A model to explain relationship between material composition feature and thickness ratio of different lithology stratum and fault throw is proposed.Based on the model,with fracture loss rate of different lithology rocks,material composition ratios,and the ratios of cataclasite and breccia in fault of coal measures are derived to explain impacts from thickness ratio of different lithology stratum R,fracture loss rate of different lithology rocks ?,and cataclasite content ratio of different lithology rocks ? on material composition feature,mineral composition and particle size distribution.(5)Field engineering examples are used to verify the impacts from material composition feature on permeability of fractured zone in fault.Results from field tests reveal that increasing mudstone content ratio improve small particles content in fractured zone in fault.The small particles can easily make internal pores and fissures of fractured rocks filled and cemented,as a result,seepage interspace is narrowed,and viscous resistance and hydraulic loss are increased.And migration of small partilces can also easily fill and narrow seepage interspace that weaken the permeability of fault fractured zone.