Experimental Study on the Pore Structure of Sandstone Damaged by Blasting and Changes in Energy Dissipation Under Triaxial Loading

Under the influence of geostress, the thick hard sandstone roof layer at the upper end of the mining area is prone to faults, rockbursts, and sudden collapses during deep coal mining. Blasting top-cutting and depressurization technology centered on over-the-top deep hole blasting is an important method for this type of dynamic disaster control. To characterize the pore structure of sandstone damaged by blast loads and the change in energy dissipation in different pressure environments, specimens with different degrees of blasting damage were measured via nuclear magnetic resonance (NMR) spectroscopy. A triaxial test loading device was used to carry out compression tests on undamaged, vibration-damaged, and blast-damaged specimens under different pressures. The effects of blast load and confining pressure on the porosity, pore structure, energy dissipation, and fracture morphology characteristics of sandstone specimens were analyzed. (1) The T2 spectral curves of the sandstone specimens were all bimodal, and the signal intensity of the main peak was much greater than that of the secondary peak. The peak T2 spectrum curves of the blast-damaged specimens and vibration-damaged specimens were 1.21 and 1.14 times greater than those of the undamaged specimens, respectively, and the mean values of the peak relative area were 1.11 and 1.20 times greater than those of the undamaged specimens, respectively. The number of internal pores in the specimens increased significantly after blast loading. (2) The pore structure distributions in the sandstone specimens were dominated by the proportions of micropores and small holes. The blast load changed the internal pore ratio structure of the specimen, transformed the small holes into medium holes and large holes, and increased the porosity of the specimen. (3) Blast load damage could reduce the energy absorption and energy storage effects of sandstone specimens and weaken roof sandstone and reduce the stress concentration. Furthermore, the impact of the blasting damage area was greater than that of the vibration damage area. (4) With increasing confining pressure, the fracture degree of the specimen first decreased and then increased. Due to the high-energy storage abilities of the undamaged specimens, the macroscopic rupture degrees of the undamaged specimens were greater than those of the specimens damaged by vibration and blasting. The blasting load will cause damage to the roof sandstone to achieve the effect of pressure relief, so as to reduce the occurrence of geological disasters such as roof fault and rock burst.