Seismic fragility assessment for cantilever retaining walls with various backfill slopes in South Korea

Abstract

We evaluate seismic fragilities for cantilever retaining walls with three slope angles of backfill (i.e., 0, 10°, and 20°), subjected to the ground motions computed for four site classes (S2, S3, S4, and S5). We collect measured shear wave velocity profiles and select representative profiles. Using one-dimensional site response analyses, surface ground motions are computed corresponding to various site conditions. Numerical models are developed for a cantilever retaining wall with a height of 4 m using the FLAC2D software, and are verified by a comparison with an analytical solution. We analyze the correlations between the seismic behavior of the retaining wall and various ground motion parameters. A probabilistic seismic demand model is introduced to calculate the probabilities of exceeding three limit states of retaining walls, based on the relative wall displacements and settlements of the backfills. We propose a suite of seismic fragility curves which are functions of either the peak ground acceleration (PGA) or cumulative absolute velocity (CAV). In addition, we propose a suite of seismic fragility surfaces using dual ground motion parameters (PGA and CAV). The results highlight that the backfill slope angle and ground motion characteristics have a primary influence on the probabilities. When the backfill slope angle increases from 0 to 20°, the probabilities of exceeding the three limit states increase by up to approximately 1.7, 4.0, and 8.5 times, respectively. Additionally, the probabilities for S3 ground motions with a PGA of 0.4 g are higher than those for S2 motions with the same PGA by up to approximately 5, 16, and 36 times, respectively.