| With the influence of mining,the original rock is broken and its pore is often changed under pressure.Since the rock is often saturated with a lot of fluids,such as gas and water,and the disturbance of in-situ stress and mining can easily induce dynamic disasters such as water and gas outburst,which threatens the safety of human life and property.Therefore,it is of great signilficance to study the characteristics of seepage and particle size distribution in pressurized broken coal and rock for the prevention and control of dynamic disasters such as water and gas outburst.In this paper,the fluid-solid coupling and fractal characteristics of broken coal rock are studied by the method of laboratory tests and the corresponding theory.The main conclusions are as follows:(1)The seepage tests of broken rocks by the size of 5?10mm are carried out by the triaxial crushing test system developed by ourselves.The porosity formula of broken rocks under three dimensional stresses is provided,and the feasibility of the system is determined.(2)Through the seepage tests under controlled confining pressure of broken sandstone,the porosity calculation formula and the variation of seepage characteristic of broken rock under three dimensional stresses are obtained.Under three dimensional stresses,after the seepage velocity and pore pressure gradient in the seepage process of broken sandstone are fitted,it is found that the seepage velocity is increasingly consistent with the Forchheimer equation,and the fitting coefficient is above O.96.Under different axial compression displacements,the seepage in broken sandstone is consistently characterized by non Darcy flow.The permeability and porosity decrease with the increase of confining pressure,and the difference decreases gradually,and finally tends to approach a stable value,which indicates that the connectivity of effective pores is weakened and the whole structure tends to be stable.(3)Concerning the seepage and fractal study of broken coal samples,the seepage and fractal characteristics of broken coal rock are tested.The steady state method is adopted to carry out seepage and fractal tests and the influence of the axial stress,gradation,porosity and fractal parameters on permeability parameters of broken coal rock are analyzed.The results show that the larger the Talbol exponent n is,the more rapidly the rate of p orosity decreases and more apparent the effect of particle recombination is.The permeability of the sample decreases with the increase of fractal dimension,and the higher the density is,the smaller the porosity is,and meanwhile,the larger the permeability is,the greater the seepage resistance is.Moreover,the characteristics of non-Darcy flow are increasingly remarkable,which is related to the particle arrangement and initial porosity,and the permeability tends to decrease.(4)According to the compression deformation of broken coal rock under dead load,the porosity and fractal dimension of broken coal rock before and after the deformation are obtained.The effects of different loads and ratios on the pore and size distribution are analyzed.The results show that the porosity and particle size of fractal dimension of broken coal with different gradation tend to be consistent with the increase of load,and with the increase of axial load,there are increasing contacts between particles and points.Both the defects of particles and axial deformation decrease.The relationship between fractal dimension of broken coal rock and different Talbol power exponent n,and the relationship between porosity and axial load are established by obtaining the corresponding parameters during dead load compression of broken coal rock.The characteristics of fractal dimension with variation of control variables are analyzed. |
PDF Full Text Request