Seismic Fragility of Gravity and Semi-Gravity Retaining Walls and Its Impact on the Functionality Loss of Road Infrastructures

Abstract

Retaining walls are key geotechnical components of road infrastructure, whose seismic performance directly affects the resilience of transportation networks. Despite their importance, seismic fragility models for retaining walls available in the literature refer only to specific case studies. Therefore, they are not applicable to all existing classes of different walls, preventing a comprehensive analysis of the impact of their seismic damage on the whole transportation networks.

This study presents a new methodology for developing fragility and functionality loss functions of gravity and semi-gravity cantilever retaining walls, suitable for large-scale applications.

The Generalized Newmark Method with Hardening (GNMH) was applied to perform thousands of nonlinear dynamic analyses on retaining wall-soil systems subjected to input motions recorded on different soil classes, considering several wall heights and critical accelerations. The latter define the capacity curve of the wall, that controls its sliding resistance.

The computed displacements resulted slightly affected by the wall configurations, while strongly influenced by the on-site seismic amplification. Such influence was considered by calibrating a predictive equation of the displacement as a function of the peak ground velocity, joint to the peak ground acceleration normalized by the critical acceleration of the wall. The calibrated predictive equation was exploited to compute fragility surfaces associated with damage thresholds, defined to be representative of the impact on the supported road. Finally, fragility surfaces were converted into functionality loss surfaces for the road, which can be used to support decision-makers in prioritizing mitigation and emergency management strategies. Considering that maps of earthquake-induced ground motion are generally available close to real time, the proposed approach would allow for a science-based decision on the action to take immediately after the earthquake.

The proposed generalized approach was successfully validated using two ideal case studies, by comparing its predictions against those obtained using site-specific fragility surfaces.