Gas Permeability Experiment for Raw Samples of Tectonic Coal Under the Condition of Negative Pressure

We use triaxial stress seepage experiment device to carry out the pressure damage experiments and the experiments of gas permeability of the raw coal sample of tectonic coal which the consistence coefficient is 0.3 under the condition of negative pressure. The results showed that it also goes through the nonlinear compressive stage, elastic stage, strain hardening stage, the stress drop stage and strain softening stage 5 stages. Under the conditions of the confining pressure and the gas pressure steady, the same axial pressure，the coal gas permeability in loading negative pressure is larger than that not loading negative pressure; gas permeability increases with negative pressure increasing. Under the conditions of the confining pressure and the gas pressure steady, the same negative pressure, with the axial pressure increasing, the gas permeability gradually increases to a certain peak then gradually decreasing. Under the conditions of the confining pressure, the negative pressure, and the pressure of gas steady, axial compression loading to σ₀ , begin to unload the axial compression, with the axial compression gradually unloading the gas permeability gradually increasing, the increasing amplitude of permeability is larger in the initial stage, then the increasing amplitude of permeability is not obvious, when the axial compression unloading to zero, the permeability is smaller than the initial permeability.