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

Layered rock masses are prone to bedding plane cracking or even large-scale collapse under impact loads such as blasting. In engineering practices, bolts or cables are commonly employed for anchoring support. This study conducted dynamic impact tests on bedded sandstone specimens under four anchoring conditions: unanchored, end-anchored, half-anchored, and fully-anchored. The effects of different anchoring methods on the dynamic mechanical properties, energy dissipation patterns, and fracture fractal characteristics of layered sandstone were analyzed. The results show: The strength of unanchored specimens decreases first and then increases with the increase of bedding plane angle, showing a "V"-shaped curve. After anchorage, the strength of the specimens is significantly improved. As the anchorage length increases, the curve gradually transforms into an inverted "V"-shaped characteristic. From an energy perspective, the transmitted energy trends of all four specimen types are similar to their strength variations. With increasing bedding angle, the reflected energy curve exhibits an inverted "V" shape, the transmitted energy gradually decreases, while the dissipated energy increases. The anchoring method primarily influences the overall magnitude of these curves. The fragments from failed specimens exhibit distinct fractal characteristics. The fractal dimension D shows an inverted "V" trend with bedding angle variation. Full-anchor specimens display the least fragmentation, while no-anchor specimens suffer the most severe damage. Based on this, the unit dissipated energy index was calculated, presenting a "V"-shaped curve. Full-anchor specimens exhibit the highest overall unit dissipated energy index, indicating their superior resistance to damage. The research findings provide valuable references for the anchoring support design of layered rock mass engineering.