Experimental Study on Rockfall Impact Force Applied to Frame Shed Tunnels

A model experiment is performed to test the rockfall impact force applied to frame shed tunnels under the protection of different types of cushions embedded on tunnel roof slabs. The changing rule of impact force induced by rockfall is analyzed according to different impact energies and types of cushions embedded on shed tunnels. An enlargement coefficient reflecting the relationship between average impact force and maximum impact force is presented using experimental data and theoretical analysis. The improved method for calculating rockfall impact force can consider the many factors that affect this phenomenon. For a particular rockfall impact energy, the rockfall impact force with different types of cushion properties is affected by the cushion property function f~(h, E, μ, γ). A large f value equates to the minimal discreteness of the expansion coefficient of rockfall impact force under different types of cushion, and vice versa.