The Role of Soil Structure Interaction in the Fragility Assessment of HP/HT Unburied Subsea Pipelines

Davide Forcellini,Hassan Karampour,Daniele Mina

doi:10.3390/jmse10010110

Abstract

Subsea high pressure/high temperature (HP/HT) pipelines may be significantly affected by the effects of soil structure interaction (SSI) when subjected to earthquakes. Numerical simulations are herein applied to assess the role of soil deformability on the seismic vulnerability of an unburied pipeline. Overcoming most of the contributions existing in the literature, this paper proposes a comprehensive 3D model of the system (soil + pipeline) by performing OpenSees that allows the representation of non-linear mechanisms of the soil and may realistically assess the induced damage caused by the mutual interaction of buckling and seismic loads. Analytical fragility curves are herein derived to evaluate the role of soil structure interaction in the assessment of the vulnerability of a benchmark HP/HT unburied subsea pipeline. The probability of exceeding selected limit states was based on the definition of credited failure criteria.

Highlights

Assessing the seismic vulnerability of critical infrastructures is fundamental in order to allocate resources toward their design and maintain a certain level of functionality for society
The first step was to validate the numerical model by comparing the fixed-based results calculated in the previous paper [6] with those obtained for SOIL1 in terms of peak ground accelerations (PGAs) and maximum stress
That resulted for SOIL2 and SOIL3 was compared (Figure 6), and linear regressions were applied to calculate the mean and the log-standard deviation (Tables 5–7) of the results of the performed non-linear dynamic analyses

Summary

Introduction

Assessing the seismic vulnerability of critical infrastructures is fundamental in order to allocate resources toward their design and maintain a certain level of functionality for society. Since pipelines are important networks for servicing communities with water, sewage, oil, and natural gas, decision makers need to carefully preserve their serviceability and resilience In this regard, buckling is one of the most critical conditions that can lead to severe failure for pipelines and was investigated over 30 years. Very few contributions have considered the effects of SSI on unburied pipelines that have been performed with finite element models. The role of soil deformability was considered by [22] to study the mutual behaviour (rock and soil layers) of the ground and the pipeline by performing a finite element model and by [23] that investigated the role of fault displacements on the buckling mechanism of buried offshore pipelines in sandy soils. The performed case study shows the importance of considering the role of SSI on the assessment of the mutual behaviour of soil deformability and structure buckling under seismic scenarios. Ref. [33] investigated the soil resistance during large lateral movements of pipelines across the seabed with particular focus on the analysis of the thermal and pressure-induced expansions

Numerical Model

Pipeline Failure Criteria

Backbone

Results and Discussion

Conclusions

Methods