Analysis and study on seepage characteristics of floor rock mass under different stress states

In order to study the change rule of floor permeability in the process of coal seam mining,Rock Top multi-field coupling test instrument was used to measure the permeability of red sandstone under different stresses by steady-state and transient methods,and the development and change rule of internal cracks and seepage characteristics during the loading process of red sandstone were analyzed. The results show that the stress difference of the rock sample is equal to 20 MPa,and the stress-strain curve is step-like. According to the crack volume strain method,the strain threshold of each stage of stress-strain can be divided into five stages:compression and sealing stage-linear elastic stage-crack stable growth stage-crack unstable growth stage-post-peak strain and failure stage;using the seepage inlet and outlet of the double pump design,using the method of steady state under five osmotic pressure difference under different stress test of rock permeability and shows that rocks permeability under different osmotic pressure difference are experiencing rapid growth slow decline-slow increase-three stages,with the stress and strain-seepage curve law is consistent,and correspond to specimen internal crack law of development;the permeability variation law under different stress differences measured by the transient method is consistent with that of the steady-state method. Due to different testing methods,the permeability of rock samples measured by the transient method is 1～2 orders of magnitude higher than that measured by the steady-state method,indicating that the red sandstone belongs to the type of low-permeability rock;applying different differential stress simulation based on complete sample floor rock mass state,found that the compression zone coal floor permeability decreases,and expansion zone permeability increase,with the working face advancing,floor permeability shows the tendency of increase with the decrease of the first,the results further reveal the with the working face advancing floor seepage characteristics of rock mass,provide important theoretical basis for prevention and control of floor water inrush.