Experimental Study On Permeability Characteristics Of Cracked Coal Rock Under Three-dimensional Stress

With the gradual extension of the depth of coal mining,the coal and rock bodies are crushed by the influence of mining to form the accumulation body.As the accumulation of coal in the deep coal mine often have to withstand high axial pressure,confining pressure and pore water pressure,which easily lead to mine water inrush and mined-out subsidence and other accidents.The study of the seepage characteristics of broken coal and rock mass is the basic task of controlling mine water inrush and mined-out area.In this paper,the seepage test of broken rock samples is carried out by applying the self-developed three-dimensional seepage test system of broken rock.The system consists of three-dimensional osmometer,hydraulic pump,relief valve and confining fluid loading system and so on.By using the axial displacement method and steady state method,we have researched the permeation characteristics of graded particle size gangue and five kinds of crushed coal samples with different osmotic pressure,different axial displacements and different confining pressures.and analysised the effects of particle size,axial displacement,axial stress,confining pressure and confining pressure on the permeability parameter of crushed coal samples,the following main research results have been obtained:(1)The porosity of the graded particle size gangue tend to decline with the increasing of axial stress or confining pressure;the permeability decrease gradually while the Darcy flow ? factor overall increases with the increasing of the confining pressure.(2)In a general trend,the permeability of graded particle size gangue declines while the non-Darcy flow ? factor of graded particle size gangue increases with the increasing of axial stress.The relationship between permeability and the non-Darcy flow ? factor is in accordance with the power function.(3)Under three-dimensional stress,the quadratic fitting phenomenon is more significant for the permeating property of crushed coal.The smaller the particle size is,the more obvious the deviation from linear fit is in the process of seepage.Porosity decreases with the increasing of axial displacement or confining pressure,and the confinement and porosity can be logarithmically fitted.(4)The permeability of crushed coal samples decrease with the increasing of axial displacement or confining pressure,and increases with the increasing of porosity ?.The non-Darcy flow ? factor of crushed coal samples increase with the increasing of axial displacement or confining pressure,and decreases with the increasing of porosity.