Evolution of permeability stress sensitivity and analysis of controlling factors for tectonic coal-bearing composites under triaxial loading

Investigating the variation patterns of the permeability stress sensitivity coefficient of coal seams is crucial for revealing the dynamic evolution mechanism of gas attenuation during the extraction process. To better conform to actual coal seam occurrence conditions,tectonic coal-bearing composites were selected as the experimental objects. Using an automatic coal-rock core permeability tester combined with the random forest method,the variation patterns of the influence of different factors on the significance characteristics of the permeability stress sensitivity coefficient were analyzed. The results indicate that as the axial pressure and confining pressure continuously increase,the permeability stress sensitivity coefficients of tectonic coal-bearing composites decrease,and the magnitude of the unit stress drop gradually diminishes. As the gas pressure gradually increases,the permeability stress sensitivity coefficient exhibits an increasing trend. As the proportion of tectonic coal increases, the permeability stress sensitivity coefficient first decreases and then increases. By establishing a random forest model, the contribution of each factor to the increase in model prediction error was calculated, and the significance of each factor was evaluated. It is concluded that axial pressure,confining pressure,and the proportion of tectonic coal are the key factors affecting the permeability stress sensitivity coefficient of coal,with mechanical factors exhibiting the most significant influence,while gas pressure has the least significant effect on the permeability stress sensitivity coefficient.