Analysis On The Interrelation Between Strata Behaviors And Gas Emission Based On Dynamics Of Solid-fluid Coupled System

Practice of coal production has shown that there is a close interrelation between strata behaviors and gas emission at mining face. When coal is excavated, the deformation of coal seam and surrounding rock occurs, and stress will re-distribute. So coal mining changes the gas adsorption, seepage and diffusion properties in coal seam, which affects the migration of gas in coal and surrounding rock. In turn, the continuous emission of gas changes effective stress and displacement in coal or rock matrix. Therefore, the mechanism of interrelation between strata behaviors and gas emission is the interaction between gas migration and coal (rock) seam deformation under stress. Based on dynamics of fluid-solid coupling system, this paper studies on the dynamic coupling between strata behaviors and gas emission at mining face using methods of experiments, theoretical analysis and numerical simulation. The response of the dynamic system is calculated by programming the presented model of coupling system between coal seam deformation and gas migration with FORTRAN. The mechanism of interrelation between strata behaviors and gas emission is revealed. The main aspects and results of this paper can be seen as follows:(1) The permeability tests in complete stress-strain process and under broken condition, the tension and compression strength test of the coal and rock samples collected from coal mine are made respectively. The adsorption parameters of coal samples are determined. The permeability test results show that maximum permeability which lags the stress peak appears in the post-peak softening stage, and decreases with confining pressure increasing. The relationship between the porosity and permeability of broken coal or rock can be expressed by power function.(2) Dynamic model of coupling system between strata deformation and gas migration is established considering the partial backfill of mined areas and support at the face. Algorithm for the system response calculating is designed and programmed with FORTRAN language. To achieve data transmission in the main program and subprogram, parameters are defined as one-dimensional array in the programming. According to the different mining states, subroutines for calculating physical in the units and on the nodes are designed for three. The calculation of physical on interface nodes among strata, filled area, unfilled area, and support is programmed in eleven situations.(3) According to geological conditions of a working face in Luan mining, the numerical model for calculating response of coupling system is established, which includes coal seam and 7 overlying strata, filling in the goaf and support action on strata. The responses of the dynamic system under 7 excavation states are calculated by FORTRAN programming. Surface figures of the destruction states and vertical normal stress distribution are presented. Curves of permeability, gas pressure and gas emission are given. Base on the calculating results, the rules of strata behavior and gas emission and their interrelation are analyzed. The numerical stability of the algorithm is discussed.(4) Dynamics model of gas migration in the region consist of rail roadway, belt conveyer roadway, tail roadway and goaf is established by Euler description. Gas diffusion coefficient, permeability and continuity of gas flow at the interface in roadway and goaf are discussed.(5) Using FLAC3D software the numerical simulation of strata behaviors and gas emission around mining face are made to study on the changes of stress and deformation (failure) on the coal (rock) seam. The influences of deformation (failure) and abutment pressure and first (periodic) weighting on gas emission are analyzed.(6) Based on the observational data of underground pressure and gas at the working face in Changcun mine, characteristics of strata behaviors are analyzed from three aspects of support load, abutment pressure and deformation of surrounding rock. Characteristics of gas emission are studied from aspect of temporal and spatial distribution of gas concentration. Temporal and spatial relation between strata behavior and gas emission at the working face is analyzed. The temporal relation is also analyzed from viewpoint of power spectrum of the support pressure and gas emission at mining face.(7) Finally, measures of reducing gas emission and corresponding hazards are proposed from three aspects of ventilation system, mining technology and gas drainage.