Research On Characteristics Of Seepage Instability Of Broken Coal And Rock Mass Based On Fractal Theory

Underground coal mine dynamic disaster is an important issue in mine accidents.Broken coal rock masses are widely distributed in the mined-out area and around the hole,with the characteristics of high permeability and easy to seepage instability.In order to prevent outburst accidents in this area of the mine,it is required to fully grasp the seepage characteristics and fractal characteristics of the broken coal rock mass,and then obtain the seepage instability mechanism of the broken coal rock mass.However,the internal pores of the broken coal rock mass are complex,random and disordered.The internal seepage mechanism still unclear due to the difficulty of measuring hole characteristics,resulting in underground gas outbursts,and the prevention of water disasters mainly relies on experience and lacks effective theoretical guidance.To this end,this paper uses theoretical derivation analysis,laboratory tests and other methods to analyze the influence of various factors on the seepage characteristics of broken coal and rock masses;determine the rule between seepage characteristics and fractal characteristics under different relative humidity through seepage and fractal tests on samples of the same proportion;basing on the theoretical derivation of the seepage instability discriminant,obtain characteristic values of seepage instability of broken coal and rock mass with the test data;Simplify the fluid flow dynamics model of the broken sample and obtain the fractal model of the permeation parameters.The work of this paper has important theoretical and engineering significance for the prevention and treatment of dynamic disasters in coal mines.The main content of the paper includes:(1)The seepage test of broken coal and rock masses with different gradation structures under lateral compression was carried out,and the variation rules of the permeability parameters of the broken coal and rock mass samples with different gradation structures were obtained;the nonlinear characteristics of the seepage process were analyzed,and the nonlinear ratio was greater than 0.5.It shows that the non-Darcy seepage can better describe its seepage state;combined with seepage instability discriminant analysis,the seepage situation is analyzed during the test process.The results show that there are critical eigenvalues when the seepage instability occurs in the broken coal sample.The seepage and instability critical Reynolds number for broken coal samples with suspended dense structure and skeleton pore structure is 3 and the critical Reynolds number for broken coal samples with dense framework is 5.(2)Using the self-developed broken rock seepage test system,combined with a constant temperature and humidity box,the seepage and fractal tests were carried out on the broken coal samples under different humidity.The results show that the increase in humidity will reduce the probability of broken samples;the quality of the coal sample crushing process-The particle size distribution satisfies the fractal characteristics,and the fractal dimension and stress satisfy the logarithmic relationship.The loading stress is less than 4 MPa,and the fractal dimension increases rapidly.The loading stress is greater than 4 MPa,and the fractal dimension growth slows down;as the loading stress increases,the permeability and fractal dimension.There is a negative correlation between the number,and a non-Darcy factor is positively correlated with the fractal dimension.The non-Darcy factor is greatly affected by the number of small particles.(3)Based on the test results and combined with theoretical analysis of the flow situation of the seepage process of the broken coal and rock mass,the critical eigenvalues of the seepage instability process of the broken coal and rock mass are analyzed,and there are different critical eigenvalues for the broken samples of different fractal dimensions.It can be used as an indicator to judge the danger of water inrush or coal and gas outburst,and it can be used as a theoretical basis for the prevention of such mine disasters.(4)Simplify the fluid flow dynamics model of a single seepage channel,and establish a fractal model of the seepage parameter when the seepage instability of broken coal and rock masses;combining the experimental phenomena and results,the model formula is verified.The results show that the relationship between the particle size fractal dimension and the non-Darcy permeability model It is better to predict the instability of seepage process.