Field, experimental, and numerical investigation of a rockfall above a tunnel portal in southwestern China

Combining the results of detailed field investigation, laboratory tests, and numerical simulations, this paper studies the rockfall problem above a tunnel portal. The mechanism of potential rock instability was analyzed, and model tests were conducted based on geological conditions and described in detail, so as to study the restitution coefficients used in programs simulating rockfall trajectory. Improvements in the tests were made in terms of experimental techniques and creative similar materials. A newly developed test bench was built by steel frames and can be assembled or disassembled at will according to requirement of model size. An innovative block-release device was adopted and controlled by computer to change the release position of block. During the model construction, the slope and blocks were fabricated with similar materials developed through quantities of mixing proportion tests. Then experiments were conducted with varied shape, mass, and release height of blocks to clarify their effect on restitution coefficients. Results indicate that restitution coefficients are apparently related to these factors and their values decrease when block mass and releasing height increase. Restitution coefficients of the wedge block are larger than those of a sphere or cuboid block. Subsequently, numerical simulations adopting the calibrated parameters were performed, and the velocities, bounce heights, and kinetic energies of rockfall along the slope profiles were obtained. Based on the research, this paper provides a useful reference for practical remediation design.