Research On Non-Darcy Seepage Law Of Pressured Fractured Coal And Rock Mass Based On Granularity Fractal Theory

With the increase of coal mining depth,the hydrogeological structural conditions faced by underground excavation have become more complex and severe,and the threat of water damage from mining has become more and more serious.The occurrence of water damage in coal mines is often related to the pressure of water in crushing coal and rock masses.In addition,the broken coal and rock mass in the mined-out area will be compacted and broken again under the action of mining stress and the overlying rock,resulting in changes in its particle size distribution and pore structure,which will affect its seepage characteristics.Therefore,studying the seepage law in the process of crushed coal and rock mass under pressure is the basis of mine water hazard prevention.In this paper,the method of combining laboratory test and theoretical analysis is used to study the nonlinear seepage law in the process of crushed coal and rock mass under pressure based on the particle size fractal theory.The compaction and creep tests of broken coal and rock masses with different humidity were carried out using the stepped loading method,and the test parameters such as creep rate,relative broken rate and particle size fractal dimension were obtained,and the creep rate with time under different axial loads was analyzed The change law of the particle size and the influence of creep time,axial stress and relative humidity on the particle size fractal dimension,the relative crushing rate increases linearly during the increase of the particle size fractal dimension.It can be obtained that the particle size fractal dimension can not only express the self-similar characteristics and particle size distribution characteristics of the crushed coal and rock mass during the re-crushing process,but also quantitatively indicate the degree of crushing of the coal and rock mass.Using a broken rock seepage test system composed of a press,broken rock infiltration device,high-pressure water pump and computer,the steady-state infiltration method was used to carry out graded loading and seepage tests on four broken samples with different initial gradations,and the breaking test was determined.Sample the porosity,fractal dimension,permeability and Euler number under the five-level axial load,and obtain the change law of seepage parameters in the process of crushed coal and rock mass under load and re-crushing and the energy dissipation in the process of non-Darcy seepage.law.Considering the fluid-solid coupling effect in the seepage process of crushed coal and rock mass under pressure,a test platform for variable mass seepage in broken rock was built from the perspective of mass loss,and a variable mass seepage test in broken coal and rock mass was carried out,and various levels of broken coal and rock masses were analyzed.The time-varying law of mass loss rate,porosity and permeability under different axial displacements,the change law of seepage parameters of broken coal and rock mass with mass loss is obtained.With the loss of the filling particles,the porosity of the broken coal and rock mass and the connectivity between the pores are greatly improved,the permeability is obviously enhanced,and the seepage velocity is suddenly changed.It can be seen that the loss of the filling particles from the boundary is caused by the broken coal and rock.An important reason for the stability of body leakage.Based on the capillary seepage hypothesis,spherical particle hypothesis and continuity hypothesis,focusing on the two research objects of fluid and solid,introducing fractal theory to study the particle size change law during the re-crushing process of crushed coal and rock mass,and applying the concept of non-Darcy equivalent permeability To characterize the non-Darcy seepage characteristics of broken coal and rock mass,and finally use Kozeny-Carman(KC)equation as a bridge to establish a particle size fractal-seepage model of crushed coal and rock mass under pressure,and use the data obtained from laboratory tests to demonstrate The accuracy and rationality of the model.