Research on gas pressure evolution law based on mining stress increment

In order to study the change law of coal gas pressure in working face under mining stress, based on the seepage consolidation model of soil mechanics, a test device composed of steel cylinder, piston and spring is designed.The device vividly simulates the force process and interaction of gas and coal body skeleton under mining stress, and then proposes excessive gas pressure and excessive gas pressure coefficient.Through theoretical analysis of the stress, volume strain and mutual relationship between gas and coal body skeleton under axisymmetric stress state, the relation between excess static gas pressure and abutment pressure is obtained based on the stress distribution law of underground coal mining.The results show that the excess static gas pressure is different from the static gas pressure, which is the gas pressure increment caused by mining stress.When the mining stress just occurs, the excess gas pressure reaches the maximum.With the progress of seepage, the excess static gas pressure is continuously dissipated, additional stress is gradually transferred to the coal skeleton, and the effective stress of the coal increases.The excess static gas pressure is directly proportional to the abutment pressure of the coal body, and the proportional coefficient is called the excess static gas pressure coefficient, which is directly proportional to the volume compression coefficient of the coal body skeleton and inversely proportional to the porosity and the gas volumetric compressibility.