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Experimental Study on Sensitivity of Porosity to Pressure and Particle Size in Loose Coal Media

A new experimental method for characterizing the porosity of loose media subjected to overburden pressure is proposed based on the functional relationships between porosity, true density, and bulk density. This method is used to test the total porosity of loose coal particles from the Guobei coal mine in Huaibei mining area, China, in terms of the influence of pressure and particle size on total porosity. The results indicate that the total porosity of loose coal under 20 MPa in situ stress is about 10.22%. The total porosity and pressure obey an attenuated exponential function, while the total porosity and particle size obey a power function. The total porosity of the loose coal is greatly reduced and the sensitivity is high with increased pressure when stress levels are low (shallow burial conditions). However, total porosity is less sensitive to pressure at higher stress when burial conditions are deep. The effect of particle size on the total porosity reduction rate in loose coal is not significant, regardless of low- or high-pressure conditions; i.e., the sensitivity is low. The total porosity remains virtually unchanged as particle size changes when pressure exceeds 20 MPa. Overall, the sensitivity of total porosity to pressure is found to be significantly higher than sensitivity to particle size.