Evaluation of the Load Carrying Capacity of a Rockfall Protection Gallery

Abstract

Mountainous areas of Switzerland are exposed to complex natural conditions, which combined with climate changes cause a variety of natural hazards. Rockfall is one of these hazards, and the risk associated with it tends to increase in recent years. The roads below the Lopper cliff at the shore of Lake Lucerne lead through one of these endangered areas. The roads are closed for traffic, following a rockfall incident in October 2009. Some rockfall protection galleries at the Lopper, which were built during 1979-1981, are subjected to a structural evaluation to allow for decisions on their further use. The current work covers estimation of the impact load carrying capacity of one of these galleries. The gallery analyzed is a cantilever pre-stressed concrete slab with variable thickness, covered by a cushion layer of soil. The behavior of the gallery is examined using finite element analyses as well as an analytical model based on a System of Multiple Degrees of Freedom (SMDF) method. The evaluation has shown that for the chosen loading case based on trajectory analyses with return periods of 30 years, the load carrying capacity of the gallery is satisfactory. However, for extreme rockfalls with return periods of 100 years, a local (punching) failure as well as a global (bending) failure can happen given that a critical section is hit