Experimental study on the mechanical characteristics of grouted coal with different crushing degrees by acoustic emission and digital image correlation

To study the mechanical and damage characteristics of crushed coal after grouting, self-developed grouting equipment was used to reinforce coal with different particle sizes. A uniaxial compression test was carried out on the grouted specimens, and the acoustic emission (AE) and digital image correlation (DIC) techniques were used to monitor the damage and deformation of the specimens during the tests. The experimental results showed that the strength and elastic modulus of specimens with medium particle size (10–15 mm) were the highest, while those with maximum particle size (15–20 mm) were the lowest. The AE events and accumulated AE counts increased with decreasing coal particle size, which indicates more internal damage during the compression process and a larger crack range and damage degree at the macro scale. The test results revealed that the failure mode gradually changed from shear failure to splitting failure with increasing coal particle size, and more coal blocks appeared to crack under compression, which indicated that the skeleton effect of grout became weaker. The DIC results showed that the deformation and local strain increased with decreasing coal particle size, and the region where displacement occurred on the surface of the specimens showed accelerated expansion during the tests.