Mining Publication: Evaluation of Polyurethane Injection for Beltway Roof Stabilization in a West Virginia Coal Mine

Extremely difficult ground conditions were encountered in the main belt entry in a room-and-pillar mine in West Virginia. Several generations of supplemental support, including cable bolts, cribbing, and Heintzmann jacks and beams, failed to halt roof falls that threatened workers' safety and the life of the mine. Polyurethane (PUR) was injected into 27 intersections in the roof, and the results were monitored by borehole video camera. The mine had averaged two to three falls in the beltway per year. Since the roof injection, no roof falls have occurred. Pre- and post-injection monitoring of test holes showed that stability can be achieved without filling all of the existing void spaces. Video logging showed that the project goal of building a beam from 2 to 6 ft into the roof was successful. Pre-injection monitoring of roof fractures uphole can delineate the zones to target for reinforcement and avoid pumping PUR into large voids to little effect. Multiple-injection zones can be identified, and the entire intersection drill hole array can be optimized based on knowledge of the fractured zones. In addition, pre-monitoring can prevent excessive hydrofracturing in solid zones. Polyurethane injection is a proven method of rock stabilization in even the weakest, most broken ground. Optimization of the injection design by preinjection video diagnostics can greatly contribute to successful and efficient roof stabilization.