Investigation of non-explosive expansion material in roof caving field application

Abstract

Effective roof caving plays a significant role in mining safety. A spatiotemporal coupling fracturing method using a non-explosive expansion material (NEEM) is proposed in this paper; this method depends on the high fracturing capacity of the NEEM and a change from vertical charging to inclined charging, aimed at producing new free surfaces step-by-step until the integrity of the entire rock is destroyed from a space-time perspective. The expansion stress and water adsorption of the NEEM were studied to determine the optimum stress increase interval and soak time. With respect to the space aspect, the charging sequence of boreholes was negatively correlated to their incline angles, bringing the NEEM's superiority into full play based on the generation of new free surfaces in steps; with respect to the time aspect, the charging intervals of the inclined boreholes were designed to obtain the best stress compensation and highest fracturing efficiency. A field trial was carried out in Pingdingshan No. 2 mine, the results of which showed that some radial cracks were produced around the charging boreholes and that they propagated to the pilot boreholes. Moreover, four main cracks were formed and were approximately parallel to the direction of the borehole rows in a fracturing group. A fracture network was eventually generated, which verified the expansion capacity of the NEEM and the feasibility of the spatiotemporal coupling fracturing method for field application.