Mechanism And Processes Of Pore Gas Pressure Change Of Gas Bearing Coal Under Coupled Static-Dynamic Loads

In order to reveal the variation mechanism and regularity of pore gas pressure of loaded coal,the control effect of volume strain and porosity change on pore gas pressure change in the process of coal deformation is analyzed.After analyzing the meso process of coal deformation by particle flow numerical model,the variation law of pore gas pressure is discussed qualitatively.The coupling effect between the change of pore gas pressure and the deformation and damage of coal is studied,and the gas-solid coupling model is established.The loading test of gas-containing coal is carried out to reveal the variation regularity of pore gas pressure under different loading conditions,and the influence of different test conditions on the change of pore gas pressure is discussed.The correctness of the gas-solid coupling model is verified by comparing the simulation results with the experimental results.The specific research results are as follows:(1)The evolution differential equation of pore gas pressure is established,which shows that the change of pore gas pressure is directly controlled by strain.The mathematical equation‘p=A₀e^?v/?'is deduced under the condition that gas quality in coal does not change,combined with the research results of the particle flow numerical simulation on porosity changes,it is shown that the pore gas pressure will rise first and then decrease during loading.(2)The interaction between coal deformation and pore gas pressure change is analyzed.A gas solid coupling model is established,which considering the effect of effective stress and adsorption expansion deformation.and the effect of effective stress and adsorption expansion deformation is considered,and a gas-solid coupling model containing gas is constructed.The model includes coal deformation equation?gas migration control equation?porosity and permeability evolution equation and damage variable model considering strain rate effect and gas degradation.(3)The experiments which can monitor the pore gas pressure is carried out.The results shown that the pore gas pressure during the loading process changes with the progressive destruction of the coal body.There are three kinds of pressure changing rules:the pore gas pressure first increases and then decreases below the initial pore pressure;the pore gas pressure first increases and then decreases,but it is still greater than the initial pore pressure;the pore gas pressure still does not decrease when the loading is completed.The mathematical equation‘p=A₀e^?v/?'fits the test results well.(4)The influence of experiment conditions on the change of pore gas pressure is analyzed:increasing the loading strain rate can shorten the time for the pore gas pressure to reach the peak;the greater the initial pore gas pressure,the smaller the change rate of pore gas pressure;the reduction of pore gas pressure develops towards a certain trend;the pore structure of coal has a complicated effect on the results of pore gas pressure changes.(5)The gas-solid coupling model is embedded in the COMSOL Multiphysics,and the numerical model is constructed to simulate the experiment.The simulation test results are consistent with the experimental results,which verifies the correctness of the gas-solid coupling model.The simulation results show the results of the pore gas pressure of experiment more reflect the process of the fracture gas pressure change,and the range of the pore gas pressure of the matrix is very small.