Study on design method of rockfall retaining pile under rockfall impact

Pile-slab rockfall retaining wall is a novel passive protective structure designed to intercept falling rocks. It is made up of cantilever piles, pile-intermediate slabs, and cushion layers. This structure features strong terrain adaptability , small footprint, and high interception height, making it applicable in high-risk rockfall areas. However, due to the lack of detailed reports on the ultimate bearing capacity of cantilever piles, guidance for engineering practice is unavailable. This paper first proposes a reasonable thickness for the cushion layer based on the characteristics of the propagation of falling rock impact forces. Then, according to the stress and deformation characteristics of the pile body, theoretical calculation methods of the internal forces and displacements of the pile body are derived using the elastic support cantilever beam model and the Winkler elastic foundation beam model, enabling the automatic determination of design parameters for cantilever pile under falling rock impact. The results indicate that for a rockfall with a diameter of 2 m, impact height of 7.0 m, impact velocity of 10 m/s, and a cushion layer thickness of 1.5 times the rockfall diameter, a double-row triple-limb steel-reinforced 1.5 m × 1.2 m cantilever pile can withstand an impact force of 2.51 × 10⁶ N and impact energy of 565 kJ. For cases with higher falling rock impact energy, it is recommended to prioritize enhancing the bending resistance of the retaining wall. This research provides a scientific basis for disaster prevention and reduction in rockfall-prone areas in the western mountainous regions of China.