Research on the impact mechanical response characteristics of gas containing coal and rock based on RSM

Abstract

To investigate the dynamic mechanical behavior of gas-containing coal in deep coal mines, dynamic compression tests were conducted on gas-containing coal using a 50 mm diameter split Hopkinson pressure bar (SHPB) system. The central composite design (CCD) method within response surface methodology (RSM) was employed to explore the effects of impact velocity and gas pressure on the mechanical and energy response characteristics of gas-containing coal. The main findings are as follows: (1) The dynamic compressive strength increases with increasing impact velocity, and the rate of strength attenuation slows down when the gas pressure exceeds 1.2 MPa. The proportion of Stage II in the stress–strain curve is greater than 50%, which dominates the energy evolution process. (2) The energy distribution is jointly governed by impact velocity and gas pressure, which is determined by pore expansion and gas adsorption/desorption. The energy evolution of gas-containing coal can be divided into three stages. As impact velocity increases, the proportion of reflection energy decreases while the proportions of transmission and dissipation energies increase; the opposite trend is observed with increasing gas pressure. (3) The energy consumption density increases significantly with increasing impact velocity, and shows a trend of first increasing and then decreasing with increasing gas pressure. Increasing impact velocity accelerates coal fracture propagation and intensifies inter-particle collisions, leading to an increase in energy consumption density by up to 48%. Increasing gas pressure loosens the coal structure and enhances energy dissipation during transfer, resulting in a decrease in energy consumption density by more than 25%. (4) Based on the RSM-CCD experiments, a two-factor, five-level regression response model with R 2 ≥ 0.93 was constructed. The interaction term AB significantly affects both dynamic compressive strength and energy consumption density, while the quadratic term A 2 of the single factor has a weak effect on compressive strength. The order of influence on compressive strength is A > B 2 > B > AB > A 2 , and that on energy consumption density is A > A 2 > B 2 > B > AB . (5) Combining the response surface methodology, the effective stress criterion, and the Drucker–Prager criterion, a statistical damage model for the strength of gas-containing coal was constructed and modified, with a model correlation coefficient R 2 ≥ 0.92. The research results can provide a theoretical basis for the prevention and control of dynamic disasters in gas-bearing coal seams in deep coal mines.