Design of passive flexible barrier against rockfall impact with 8000 kJ energy level

The protection level and domestic standard test level of commonly used passive flexible barrier against rockfall impact are not higher than 5000 kJ, while bridges in mountains and other important transportation infrastructures are facing rockfall disaster threat with higher impact energy level. The analysis and design of 8000kJ-level passive flexible barrier against rockfall impact were carried out at present based on the numerical simulation method. Firstly, by adopting the explicit dynamic software ANSYS/LS-DYNA, quasi-static tests including the tensile test on single wire ring and three-ring chain, net puncturing test, and the dynamic impact test, i.e., 2000 kJ rockfall impacting the full-scale passive flexible barrier, were numerically reproduced, and the reliability of the numerical simulation method was fully verified by comparing with the experimental data, i.e., the maximum breaking force and breaking displacement of the wire ring and its failure characteristics, the whole impact process of rockfall and the cable force-time history curves. The influencing factors, i.e., the inclining angle, span, height of the steel post, and different specifications of energy dissipating devices ranging from 50 kJ to 70 kJ on the dynamic behavior of the passive flexible barrier were further analyzed. The results showed that: the specification of energy dissipating device is the most critical parameter controlling the internal force and displacement of the passive flexible barrier; the inclining angle of the steel post is recommended to be taken as 10°; the increase of the post spacing can reduce the in-plane stiffness of the structure, while having less effect on the transverse anchorage; the increase of the post height will cause a significant increase in the support reaction force at the post bottom; the reasonable adjustment of the anchorage position of each wire rope is required when the post height and spacing are changed. Finally, based on the results of parameter analysis, two design schemes for passive flexible barrier against 8000 kJ rockfall impact were given by adjusting the geometry of the structure, the specification of the energy dissipating device, and the addition of transmission support ropes, and both of them passed the test of the European standard EAD 340059-00-0106.