No abstract

Damage to buried pipelines caused by local amplification of seismic ground motion in highly nonuniform grounds is not yet fully understood. The development of methods to evaluate the amplification of ground motion in complex ground structures is thus desirable. Here, we report large-scale nonlinear seismic ground response analysis using a 3D nonlinear finite element method (FEM) and attempt to reproduce observed seismic ground motion. We also discuss the strain amplification processes and their effects on buried pipelines in detail. The findings are expected to aid in improving the seismic resistance of buried pipelines.

During seismic events, buried pipelines are subjected to deformation by seismic ground motion. In such cases, it is important to ensure the integrity of the pipeline. Both beam-mode and shell-mode buckling may occur in the event of compressive loading induced by seismic ground motion. In this study, the beam-mode buckling of a buried pipeline that occurred after the 2007 Niigataken Chuetsu-oki earthquake in Japan is investigated. A simple formula for estimating the critical buckling strain, which is the strain at the peak load, is derived, and the formula is validated by finite-element analysis. In the formula, the critical buckling strain increases with the pipeline diameter and hardness of the surrounding soil. By comparing the critical strain derived in this study for beam-mode buckling with the critical strain derived in a past study for shell-mode buckling, the formula facilitates the selection of the mode to be considered for evaluating the earthquake resistance of a pipeline. In addition to the critical buckling strain, a method to estimate the deformation caused by seismic ground motion is proposed; the method can be used to evaluate the earthquake resistance of buried pipelines. This method uses finite-element analyses, and the soil–pipe interaction is considered. This method is used to reproduce the actual beam-mode buckling observed after the Niigataken Chuetsu-oki earthquake, and the earthquake resistance of a buried pipeline with general properties is evaluated as an example.

During seismic events, buried pipelines are subjected to deformation by seismic ground motion. In such cases, it is important to ensure the integrity of the pipeline. Both beam-mode and shell-mode buckling may occur in the event of compressive loading induced by seismic ground motion. In this study, the beam-mode buckling of a buried pipeline that occurred after the 2007 Niigataken Chuetsu-oki earthquake in Japan is investigated. A simple formula for estimating the critical strain, which is the strain at the peak load, is derived, and the formula is validated by finite-element analysis. In the formula, the critical strain increases with the pipeline diameter and hardness of the surrounding soil. By comparing the critical strain derived in this study for beam-mode buckling with the critical strain derived in a past study for shell-mode buckling, the formula facilitates the selection of the mode to be considered for evaluating the earthquake resistance of a pipeline. In addition to the critical strain, a method to estimate the deformation caused by seismic ground motion is proposed; the method can be used to evaluate the earthquake resistance of buried pipelines. This method uses finite-element analyses, and the soil–pipe interaction is considered. This method is used to reproduce the actual beam-mode buckling observed after the Niigataken Chuetsu-oki earthquake, and the earthquake resistance of a buried pipeline with general properties is evaluated as an example.

We demonstrate a comprehensive earthquake response analysis method for improving the seismic input force estimation of buried pipelines by combining ground motion and soil amplification analyses. Using this method, the seismic input force of an actual pipeline was estimated and its seismic performance was checked for a largest assumed seismic fault scenario. Three-dimensional inhomogeneity of ground and surface topography is known to greatly affect the results of ground motion and soil amplification analyses. To consider these effects, a linear wave propagation analysis using a 10 × 109 degree-of-freedom three-dimensional finite element model was conducted for the ground motion analysis, and a nonlinear wave propagation analysis using an 80 × 106 degree-of-freedom three-dimensional finite element model was conducted for the soil amplification analysis. The application example showed that three-dimensional inhomogeneity of ground and surface topology caused complex seismic input forces to buried pipelines, and demonstrated the effectiveness of the comprehensive seismic analysis method proposed in this study.