Experimental study on dynamic mechanical properties of sandstone under coupled effects of bedding dip angle and anchoring methods

Layered rock masses were prone to bedding plane cracking or even large-scale collapse under impact loads such as blasting. In engineering practices, bolts or cables were commonly employed for anchoring support. To investigate the dynamic mechanical response of layered rock masses under impact loading and the effectiveness of bolt support, sandstone specimens with different bedding dip angles (0°, 15°, 30°, 45°, 60°, 75°, 90°) and bolt support methods (no-anchor, end-anchor, semi-anchor, full-anchor) were prepared. Dynamic impact tests were conducted using a split Hopkinson pressure bar (SHPB) system to analyze the coupling effects of bedding dip angle and bolt support method on the dynamic strength, energy evolution, and failure modes of the rock mass. Additionally, fractal theory was employed to quantitatively characterize the fracture characteristics of the specimens. The results indicate that the strength of unanchored specimens initially decreases and then increases with increasing bedding plane angle, exhibiting a V-shaped curve. After anchoring, the strength of specimens improves significantly, and as the anchor length increases, the curve transitions to an inverted V-shape. From an energy perspective, the transmitted energy trends of all four specimen types are similar to their strength trends. As the bedding plane angle increases, the reflected energy curve shows an inverted V-shape, the transmitted energy gradually decreases, while the dissipated energy increases. The anchoring method primarily affects the overall level of the curves. The fragments of the specimens after failure exhibit distinct fractal characteristics, with the fractal dimension curves showing an inverted V-shape influenced by the bedding plane angle. Full-anchor specimens display the least fragmentation, while no-anchor specimens experience the most severe damage. Based on this, the unit dissipated energy index was calculated, revealing a V-shaped curve. Full-anchor specimens exhibit the highest overall unit dissipated energy index, indicating their superior resistance to damage. The findings of this study can provide a reference for anchor support design in layered rock mass engineering.