Evaluation research of the fracturing capacity of non-explosive expansion material applied to coal-seam roof rock

Goaf caving is an effective measure to prevent disasters caused by large area roof weighting (LARW). This study uses non-explosive expansion material (NEEM) as a crack source to initiate goaf caving. To evaluate the fracturing capacity of NEEM, we prepared similar specimens with and without an included layer, and different numbers of slots were made along the radial direction of the hole. Acoustic emission and static strain gauge were adopted to monitor energy release and fracture strain damage. All the specimens displayed complex fracture phenomena, and there were positive correlations between fracture number and fractal dimension, fracture density, and the degree of faulting. The fractal dimension and fracture density of layer-bearing specimens were greater than those of specimens without a layer. The released cumulative energy was higher for specimens with two slots than for those with no slots, for specimens both with and without layers. Overall, compared to non-layer specimens, layer-bearing specimens showed a more concentrated energy ratio and a longer duration time of energy release. The relative cumulative energy curves showed several stable rising and abrupt rising patterns, which prolonged the action time of rock internal energy accumulation and accelerated the accumulation of internal damage.