Dynamic properties of rock bolted by high performance NPR anchor bolts with different preloads

NPR (Negative Poisson's Ratio) bolts are advanced support materials engineered for stabilizing deep underground excavations, distinguished by their exceptional deformability and energy absorption capacity. This work examines how bolt preload affects the dynamic response of bolted rock with NPR bolts, compared with rock bolted by conventional PR (Poisson's Ratio) bolts. The results demonstrate that key dynamic performance indicators—including dynamic compressive strength, dissipated energy density, dissipated energy ratio, and impact toughness—exhibit a positive linear correlation with increasing preload for both anchorage types. While higher preload generally enhances the post-failure integrity of bolted rock, excessive preload adversely affects the structural soundness of PR-bolted rock. Importantly, NPR-bolted rock consistently demonstrates superior dynamic performance under identical preload conditions. The mean fragment size dm of NPR‑bolted rock scales linearly with preload, whereas that for PR‑bolted rock follows a quadratic path, rising initially and then declining. Based on a comprehensive evaluation of the impact toughness index and dm growth rate, the optimal preload ranges are determined as 40%–60% for PR-bolted rock and 60%–80% for NPR-bolted rock.