Research on the fractal characteristics of the micro/nano-mesoscopic pore structure of high-rank coal under impact loads

Abstract

ABSTRACT To reveal the mechanism of impact load on coal micropores and improve the extraction efficiency of high-rank coal gas, a separate Hopkinson pressure bar (SHPB) impact test system was used to simulate the shock and stress waves of the impact stress in different attenuation processes. Based on mercury intrusion and low-temperature liquid nitrogen test data before and after impact, fractal theory was applied to study the micropore fractal characteristics of high-rank coal in different directions before and after impact in the Chengzhuang Mine. The results show that pores smaller than or equal to 100 nm based on mercury intrusion data and pores larger than or equal to 100 nm based on low-temperature liquid nitrogen data do not follow fractal rules. Impact loads reduce the seepage and adsorption pore fractal dimensions. Although the seepage and adsorption pore fractal dimensions do not decrease with increasing impact load, a minimum fractal dimension occurs. The impact load corresponding to the minimum seepage and adsorption pore fractal dimensions in the same direction is the same. Impact loads increase gas migration velocities of the seepage pores, reduce the adsorption capacity of the adsorption pores, and promote gas desorption. The research results are important for determining the optimal drainage hole layout and examining the impact cracking and infiltration mechanism.