Seismic stability of a reinforced-soil structure constructed after the mid-Niigata prefecture earthquake

The mid-Niigata prefecture earthquake in 2004 damaged a number of structures, including embankments, earth slopes and retaining walls. This paper describes a selected collapsed earth slope constructed in a valley eroded by the Shinano River with low-permeability backfill soil. The failure mechanism of the earth slope is shown by the high response acceleration at the crest owing to the low stiffness and strength of the backfill soil. The paper also describes numerical techniques to evaluate the performance of the structure constructed before and after the earthquake. For the selected earth slope, the response acceleration during the earthquake and the groundwater level before the earthquake were estimated by finite element (FE) analysis. Deformation analysis was conducted using Newmark's sliding-block analysis, which implements the estimated groundwater level and response acceleration of the structure subjected to the earthquake by the above FE analysis. According to the results of the numerical analysis, it is important for geosynthetic reinforcement to increase the stiffness of the reinforced soil to allow for a decrease in the deformation at the crest of the structure. The numerical analysis in this study revealed that the performance of the reinforced retaining wall constructed after the earthquake is significantly better than that of the collapsed earth slope constructed before the earthquake.