A Study on Stress Redistribution of Roadway Sidewall after Hydraulic Fracturing in Coal Bumps Prevention

Abstract

Hydraulic fracturing is an effective mean to prevent coal bumps in deep coal mining. The calculation of stress redistribution of coal sidewall after hydraulic fracturing can evaluate the fracturing effect and provide a reference for the hydraulic fracturing scheme design. In this paper, a theoretical model of stress redistribution of roadway sidewall after hydraulic fracturing is established with considering the effect of crushing zone. And the influences of the water injection length and the fracturing radius on the stress redistribution of roadway sidewall are investigated. The results show that the water injection section should be set at a deeper position with considering the existence of the crushing zone. The coal roadway sidewall after hydraulic fracturing is divided into five zones: the crushing zone, the shallow plastic zone, the pressure relief zone, the deep plastic zone, and the elastic zone. The stress redistribution law is obviously affected by the water injection section length and fracturing radius. With the increase of water injection length or fracturing radius, the pressure relief effect is more evident, but the axial force of rockbolt increases gradually. In order to acquire a better pressure relief effect, the matching of the water injection length and the fracturing radius should be considered crucially in the hydraulic fracturing design for preventing coal bumps.

Anchorage weakening effect of coal roadway sidewall with different destressing borehole diameters

“…The maximum boundary of the influence range of the destressing borehole on the rockbolt should be on the connecting line between the destressing borehole center and the anchorage hole center. Referring to the elastic–plastic distribution stress model of the circular cavern 28 and the equation of static equilibrium, the stress distribution of the position can be obtained as follows. $$${\sigma }_{\theta f}=\frac{{\sigma }_{{c}_{f}}}{{\xi }_{f}-1}\left[{\xi }_{f}{\left(\frac{R}{{R}_{a}}\right)}^{{\xi }_{f}-1}-1\right],$$$ $$${\sigma }_{Rf}=\frac{{\sigma }_{cf}}{{\xi }_{f}-1}\left[{\left(\frac{R}{{R}_{a}}\right)}^{{\xi }_{f}-1}-1\right].$$$…”

“…The maximum boundary of the influence range of the destressing borehole on the rockbolt should be on the connecting line between the destressing borehole center and the anchorage hole center. Referring to the elastic-plastic distribution stress model of the circular cavern 28 and the equation of static equilibrium, the stress distribution of the position can be obtained as follows.…”