Vulnerability of existing rockfall protection galleries

In Switzerland, the guideline for the design of rockfall protection galleries has been revised with the aim of accounting for the structural dynamic behaviour, the probability of failure, and the acceptable risk levels associated with uncertainties in predicting the impacting rock mass and velocity. The introduction of calibration factors enables the straightforward application of static equivalent impact forces together with the current national structural codes. Different factors are proposed according to acceptable risk levels, considering consequences, cost efficiency, and the level of confidence in the prediction of loading, to improve the level of protection. The purpose of this approach is to promote the assessment of existing structures using this methodology and to demonstrate its applicability to other types of loading scenarios. The vulnerability curves of galleries were evaluated using a nonlinear dynamic finite element tool (XDEEA) and validated through comparisons with existing studies (LS-DYNA analyses and experimental data). Pushover analyses were carried out by increasing the impact velocity until a defined failure criterion was reached. Based on the generated vulnerability curves, the loading conditions were incrementally increased until the target reliability indices were achieved, depending on the assumed uncertainties. As a result, calibration factors consistent with the social importance (consequences) of the gallery and the desired structural performance level were obtained. The resulting correction factors in comparison to the current design guideline demonstrate the potential of a performance-based design approach while maintaining a simple and practical design methodology for engineers. The presented approach can also be applied to other loading conditions.

Keywords: existing protection gallery, finite element method, target reliability, uncertainties, vulnerability curve, correction factor.