Avalanche Barriers in the starting zone exposed to rock fall: Range of capacity and 1:1 rock fall tests with flexible snow net

Since the introduction of flexible snow nets in the 1950’s it became obvious that such\nbarriers provide a better performance on combined loadings of static snow pressure and dynamic\nrockfall impacts compared to stiff steel bridges. In various cases avalanche barriers in the starting\nzone have to be built under rock faces with frequent rockfall. On a qualitative basis it was found that\nrigid systems e.g. snow bridges made of steel are not able to withstand rock fall energies of more than\n50 kJ. This is the result of a research project and case studies in Switzerland, Austria and Germany\ntogether with the alpS - Zentrum für Naturgefahrenmanagement and WSL- Institute for Snow and\nAvalanche Research SLF (Margreth 2006a and b). The investigations have shown that flexible snow\nnets have a higher energy absorption capacity which may be even more than 200 kJ. To obtain a better\nunderstanding of the interaction and performance of rock fall on snow nets and to quantify the capacity\nof snow nets a trial of 4 different 1:1 large scale rockfall tests with flexible snow nets have been\ndone. With this testing it is possible to quantify the rockfall capacity of a new type of snow net. Integral\npart of this snow net is a rhomboidal spiral rope net with a load capacity of 220 kN/m’. The rockfall\nbearing capacity could be even increased by applying stronger spiral rope nets. As a result it was possible\nto achieve a rock fall capacity of up to 500 kJ which is ten times more compared to rigid structures.\nThis rockfall adapted snow net system has been already installed in Austria. In this paper the\nproject is presented and detailed information about the performed test series is provided. The results\nof our technical development are improved flexible avalanche supporting structures which can withstand\nrockfall energies up to 500 kJ leading to reduced costs for maintenance and repair respectively.