Research Non-Darcy Seepage For Broken Rock Mass And Its Application

The broken rock in coal mining can be divided into two kinds:one kind is accumulation of broken rock mass, the broken rock mass is caused by engineering excavation and can be compaction again under the effect of high pressure, such as the overburden accumulation rock is caused by mining action. Another kind is in situ broken rock mass, i.e. the mass which is broken by construction and mining action is still in the original position, such as fault fracture zone, loose mass after excavation of roadway, etc.Broken rock mass compared with complete, density of rock mass, has high porosity, high permeability characteristics, therefore, major disasters and accidents caused by seepage happened in fractured rock mass. Research of broken rock mass seepage is a basic research, has important theoretical significance. Major disasters and accidents caused by seepage major happened in fractured rock mass. The research of broken rock mass seepage is a basic research, linked with mining engineering; petroleum engineering; underground engineering and a series of related field, to promote production safety have important theoretical and practical significance.Firstly,according to the high porosity, high permeability, and fractal distribution characteristics of broken rock, this project combines the fractal geometry theory and technology in nonlinear mathematics with the dynamics of fluids in porous media, and establishes a fractal mathematical model for non-Darcy seepage characteristics of the broken rock. Proposed a fractal drag force model for flow in the loose packed and fractured rock mass.The new model reveals that not only the capillary model, but also the drag force model can be used to describe fluid flow in porous media. Fractal analysis revealed the mechanism of fractal dimension and tortuosity effect on fluid flow, put forward that the drag coefficient is changed from 10～13 when the Reynolds number is 20～1000.Secondly, this paper further studys the pore throat model, by comparing the average hydraulic radius of pore throat model and Forchheimer equations, obtains the analytical expressions of Darcy permeability, non-Darcy factor, non-Darcy equivalent permeability, and the ratio of non-Darcy equivalent permeability and Darcy permeability. Darcy permeability is the function of porosity, average particle size, is not the function of Reynolds number. The conclusion is consistent with the permeability definition that permeability is related to medium skeleton and has northing to do with the fluid flow in the medium. Non-Darcy equivalent permeability is a function of the Reynolds number and decrease with the increase of Reynolds number; it is the same with dimensionless results of Barree and Conway’s. Using dimensionless form for non-Darcy equivalent permeability, get the ratio of non-Darcy equivalent permeability and Darcy permeability. Mining engineering and petroleum engineering often used Darcy seepage, ignored non-Darcy seepage. This may cause a great error, in practical application, which can use the ratio of non-Darcy equivalent permeability and Darcy permeability to modify Darcy permeability, this will reduce the error. This paper get the critical Reynolds number of Darcy and non-Darcy flow in rock is 0.1.when Reynolds number is less than 0.1, the ratio of non-Darcy equivalent permeability and Darcy permeability is larger than 99%, the error caused by non-Darcy seepage is less than 1%, the fluid flow in the porous medium is Darcy flow; When Reynolds number is greater than 1, the ratio of non-Darcy equivalent permeability and Darcy permeability is less than 95%, the error caused by non-Darcy seepage is larger than 5%, fluid flow in the porous medium is non-Darcy flow. This paper extends the average hydraulic radius of pore throat model to gas liquid two phase flow, the expression relative permeability, and relative non-Darcy factor are obtained.Finally, this paper introduces the Forchheimer type non-Darcy flow theory, i.e. fractal model, Ergun equation, the average hydraulic radius and pore throat model, to calculate of mine water disaster prevention and control.It provides theoretical for mine water inrush and fire prevention and control. Respectly get water inrush critical threshold value. From the perspective of nonlinear dynamics system structure instability reveals the mechanism of coal mine water inrush. Research has shown that mine water inrush and rock porosity, particle diameter, fluid seepage mechanics properties is the function of porosity, particle diameter, fluid seepage mechanics properties, flow speed and other factors, when the porosity and particle diameter is smaller, seepage is not easy to lose steady state; Conversely, porosity and particle diameter is larger, seepage is easy to lose steady state.This paper established a "three zone" series resistance model; introduce non-Darcy seepage into calculation air leakage in mine roadway. The seepage coefficient is calculated by average hydraulic radius and pore throat model, is the function of porosity, particle diameter and other factor. We choose an adjacent goaf, straight,410m roadway to measure the volume of mine, the model prediction values consistent with the experimental results. This verified the validity of the model. This project will help us to understand the transport law of porous media which has high porosity and high permeability, to make up the existing research theory of high speed flow, to solve the hypertonic problem of mining, petroleum, groundwater and geology engineering, to expand the practical application of the nonlinear flow field.