For difficult hazard zones with large rock sizes, high falling and bouncing height with immediate effect the new high-energy rockfall barriers RXI-300 and RXI-500 are available as alternative to protective concrete structures. The RXI-300 and the RXI-500 high-energy barriers surpass the impact absorption capacity of most concrete galleries in use as well as in the process of planning.
The RXI-500 stands for a rockfall barrier with an energy absorption capacity of 5’000 kJ. To produce a 5000 kJ impact energy a test body of reinforced concrete with an edge length of 1.9 m and weight of 16 tons is released in free fall from 32 m above the rockfall barrier, impacting the barrier with 90 km/h. This vertical freefall crash test procedure, the most stringent in the world, was introduced by the Swiss Federal Office for the Environment FOEN in 2001 to obtain the approval for barriers against rockfall. This crash test was performed by Swiss Federal Institute for Forest Snow and Landscape Research WSL.
The main part of this tested rockfall barrier is the ring net which stands out for its outstanding energy absorption properties. The ring nets are supported by steel wire ropes which are guided through brake rings – pipes bent into loops – which in larger rockfall events as they contract will dissipate the residual energy from the ring net and allow for additional braking distance. To obtain the barrier height steel posts are used, which are fastened to ground plates with hinge pins and held in position by retaining ropes. The height of the tested barrier was 6 m with a post spacing of 10 m.
The entire braking process of the impacting test body of 16 tons hitting the barrier with 90 km/h took hardly more than 0.5 seconds. The measured braking distance of approximately 9 m was well below the admissible value of maximum 15 m. This value is relevant to determine the proximity of the installation relative to the object to be protected. The residual useful barrier height in the impact section required to obtain the certification requires to be above 50 %. A first visual inspection revealed that this value was achieved with the RXI-500 and that the useful height in the neighbouring fields after the impact was still almost 100 %.
The maximal rope forces measured were in the magnitude of approx. 240 kN, which is a very low value considering the high energy class of the RXI-500. This is explained by the fact that the impact force dissipation is spread over the barrier as well as further developments in the braking process elements. The forces generated by the impact can be absorbed by the ground anchors. No anchors with higher load capacity are necessary, which would have required higher class drilling equipment and an increase in installation cost.
Worldwide the high-energy rockfall barrier RXI-500 is the strongest crash tested rockfall protection available on the market.