Experimental study on damage and seepage features of gas bearing sandstone under different impact velocities loading

Abstract

Using an impact damage-percolation experimental system for gas bearing coal or rock and an industrial CT scanning system, the authors design and carry out a series of dynamic compression-seepage tests for loading at different impact velocities under triaxial prestressed states and reconstruct the three-dimensional crevices structure of the impact-damaged sandstone in order to reveal the law of damage features and permeability of the gas bearing sandstone under different impact loads. The experimental results of dynamic stress-strain curve characteristics, energy dissipation laws, damage and permeability evolution features under different impact velocities loading of fluid-solid coupling sandstone samples show that as the impact loading velocity increases, the strain rate of the gas bearing sandstone increases. The incident wave energy, reflection wave energy, transmission wave energy and absorption energy increase simultaneously as well. The peak stress and peak strain of gas bearing sandstone increase with the impact velocity as well, and the compaction stage in the dynamic stress-strain curve is constantly compressed until it disappears completely. The failure form of gas bearing sandstone is mainly shear failure under the condition of triaxial static and gas-solid coupling. With the increase of impact velocity, the number of tensile cracks under the combination of impact load and gas pressure increases continuously. Poisson's ratio effect and eccentric compression form two types of tensile cracks along the axial direction or perpendicular to the sample. The two types of tensile cracks are connected along the outer edge of the specimen, showing a grid shape. Nascent cracks are interconnected, which drives macroscopic through cracks formation. The absorption energy of gas bearing sandstone directly determines the degree of damage. The increasing absorption energy not only increases the damage degree of gas bearing sandstone after damage, but also greatly improves the permeability. The permeability of gas bearing sandstone after impact damage follows a linear positive correlation with its crack rate.

Keywords

• gas bearing sandstone
• gas-solid coupling dynamic damage shpb test
• in-situ permeability tests
• industrial ct scanning
• cracks extension and remodeling