Soft coal solid-gas coupling similar material for coal and gas outburst simulation tests

The adsorption, permeability properties, and damage evolution of internal cracks are often not considered in simulation tests for coal and gas outbursts. Therefore, in previous studies of similar materials, the materials used may not be similar in the properties mentioned above. To solve these issues, the adsorption, permeability, mechanical, and acoustic emission (AE) response characteristics of a soft coal solid-gas coupling similar material (SCSCSM) were studied in an orthogonal experiment where gas adsorption, permeability, uniaxial compression, and AE tests were performed. The analysis of the experimental data revealed that the SCSCSM has mechanical, gas adsorption and permeability properties similar to those of soft coal. The mass fraction of humic acid sodium solution (HASS) was the main parameter, affecting physical and mechanical properties. As the mass fraction of HASS increased, the adsorption volume and permeability varied logarithmically and exponentially, respectively. Meanwhile, the failure pattern transitioned from extrusion damage to wedge splitting and brittle shear failure. AE response from the beginning to the peak stress can be divided into a slow increase stage and a rapid increase stage. A damage parameter experienced an initial rise, then a rapid decline, then a quick rise, and finally a slow increase. Through segmentation fitting, expressions of damage evolution mechanisms for each section were obtained. Through the study of the SCSCSM's internal gas storage, transport, and mechanical properties, AE response characteristics, and multiscale evaluation of mechanical response, this study has laid a foundation for the subsequent development of solid-gas coupling similar simulation materials and physical simulation experiments of coal and gas outburst for soft coal seams.