Experimental Study On Solid-liquid-gas Coupling Mechanism And Gas Migration Law Under The Influence Of Mining

In this paper,Nanchuan-Hongneng Coal Industrial Company,west K1 coal bed of ban-xi coal factory is chose as the research object.From the macroscopic aspect of coal,the permeability test of coal under solid-liquid-gas coupling in-situ stress field,the mechanics and permeability test of coal under solid-liquid-gas coupling mining pressure field and the mechanics and permeability test of coal under cyclic mining stress field was made by using self-developed 'coal containing gas thermal hydrological mechanical(THM)coupling experimental equipment'.And the mechanical and permeability characteristics of coal and rock under different stress fields and different hydro geological conditions are analyzed.From the mesoscopic aspect of coal,the meso-shear test of coal under different water content was made by using self-developed'meso-shear test equipment for coal rock containing gas'.The shear crack evolution law of coal under different water content is compared and analyzed.Based on the above experiments,the main conclusions can be obtained:(1)When the coal rock is in the in-situ stress field,with the increase of confining pressure,the effective permeability of coal decreases gradually,and the decreasing trend is more and more gentle.With the increase of water content,the permeability of coal sample decreases gradually,and the decreasing trend is more and more gentle.(2)When the coal rock is in the mining pressure field,with the increase of moisture content,the bearing strength,residual strength and deformation modulus of loading-unloading coal samples all present a trend of decrease.However,the axial strain,lateral strain,volumetric strain and lateral expansion ratio all show a trend of increase.Before coal samples damage the higher the moisture content is,the lower methane gas effective permeability is.Conversely,after coal samples damage the higher the moisture content is,the higher methane gas effective permeability is.With the increase of moisture content,the damage,fracture development and deformation of coal samples show a trend of increase.The total energy and the dissipation energy of coal samples present a trend of increase during the whole loading-unloading process,in contrast,the elastic strain energy presents atrend of decrease.(3)When the coal rock is in the deep cyclic mining stress field,with the advancing of cyclic loading-unloading,the cumulative residual deformation increases gradually,the relative residual deformation first decreases,and then appears the residual deformation stability zone,and then rises when the coal sample is destroyed.With the advancing of cyclic loading-unloading,the overall trend of permeability is to begin to spiral down,after which the spiral rise,the sudden sharp increases when coal sample destruction.(4)The absolute recovery rate of permeability and relative recovery rate of permeability are defined as ?j and ?x to quantitatively analyze the change of permeability in the process of loading and unloading,?j decreases firstly,then increases,?x increases gradually,?x stands at 85%?950%in elastic stage,?x more than 100%near the destruction of coal.With the advancing of cyclic loading-unloading,the cumulative dissipated energy increases as an exponential function,and the damage variable equation is established with the dissipation energy:D=2/? arctan(?? exp[?(?1-?3)]}(5)When the coal rock is in the shear stress field,the higher moisture content of coal sample is,the shorter time of the initial crack initiation is,the more main cracks formed,the more easily the broken zone is in the coal sample surface,the more complex the shear crack shape.