Quantitative back analysis of in situ tests on guiding flexible barriers for rockfall protection based on 4D energy dissipation

This paper presents a quantitative analysis of system dynamic response, rockfall trajectory control, and kinetic energy evolution of the tests on the guiding flexible protection system (GFPS) based on 4D energy dissipation. The system achieves 4D protection against rockfall hazards on high and steep slopes, with 3D spatial motion and energy evolution control of rockfall trajectories in time history. After clarifying the structural principle of the system, analyzing the kinetic energy characteristics of the rockfall along the hill, and defining the multistage energy-dissipation control principle of the system, an evaluation method for rockfall energy evolution for quantitative back analysis was established for the whole course of system protection. Furthermore, the rockfall’s energy decay characteristics in the guiding section were analyzed. Accordingly, a full-scale model of this system was constructed, and six in situ tests with and without the protection system were conducted. The system model was laid on a slope with a gradient of over 60°, a width of 130 m, and a height of 82 m, where the crushed rock developed. The maximum impacting energy was 2500 kJ. Quantitative back analysis of the experiment was carried out, and the results revealed that, compared with the unprotected tests, after the construction of the protection system, the motion duration of the falling block was extended by over 80%, the impact times increased by approximately five times, the bounce height reduced by roughly 80%, the transverse motion distance reduced by around 50%, and, for blocks that reached the bottom, the residual kinetic energy and the rolling distance away from the slope toe were both decreased by 70%. The combined energy-dissipation ratio was as high as 89%.