Impact of Micro-NPR bolt on the mining of deep-buried phosphate via the room-and-pillar method

Abstract

Large and complex goaf groups have formed as a consequence of mining activities in the Yichang Phosphate Mine. These goaf formations have given rise to recurring engineering challenges and disasters, including roof collapse and pillar damage, primarily attributed to excessive ground pressure. Owing to the working principle and mechanical properties of traditional PR bolts, the preload cannot be applied to the surrounding rock immediately after excavation, resulting in considerable roadway damage. To address the problem of large deformation control in deep mines, a damage mechanics model of a roof-and-pillars mine was established to analyse its deformation and damage characteristics. A physical model experiment was performed to analyse the damage state of the roof and pillars in a deep-buried phosphate mine with twin roadways using the room-and-pillar method. The objective was to examine the effectiveness of the PR and micro-NPR(negative Poisson's ratio) bolt support systems under real conditions. Experimental results indicated that the micro-NPR bolt effectively strengthened the roof and pillar, enhanced the strength and stiffness of the pillar, and prevented pillar extrusion and roof collapse. These findings bridge the gaps in the existing theoretical frameworks, technical research, and engineering applications of the micro-NPR support, promoting technological innovation in the phosphate mining industry. This study provides a reference for the state change and support research on the surrounding rock after the excavation of twin parallel tunnels under specific conditions.