Effects of the soil spatial variability on pipelines
Abstract
Pipelines are the safest and most efficient way to transport large volumes of oil and gas from extraction fields, to refineries, industry and home consumption. Extensively used to transport fluids over long distances, pipelines may pass through terrain features exposed to geohazards. The performance of buried pipelines in areas subjected to ground displacements constitute a criterion for design, assessment and management of gas pipelines, to ensure public, environment and property safety in a cost-effective manner. Modern surveying and sampling techniques allow for better geotechnical characterization of ground movements and the variability of the soil properties with confidence. The statistical data enables reliable models to correlate the inspection measurements with the overall safety of the buried pipelines.
Random field theory is widely used to model spatial variability of soil properties that affect the probability of failure of pipelines. A limit state for onshore gas pipelines laid down over hill-type features is Upheaval Buckling (UHB). In this study, the spatial variability of the soil properties is considered in a simplified manner. The soil correlation structure is idealized as a multivariable cross-correlated Gaussian random field. A parametric example illustrates the impact of the spatiality variability of the soil on the failure probability due to UHB and the applicability of simple empirical equations to account for the spatial variability of soil. The analysis results suggest that accounting for the soil spatial variability of the soil may lead to less overconservative estimation of failure probability due to the risk of UHB.
A practical approach to analyze probability of failure of pipelines susceptible to landslides is presented. Soil displacements can impose significant loads to pipelines, which might eventually result in the failure of pipelines along unstable slopes. A simple procedure to estimate tensile rupture and compressive local buckling is presented. The soil is characterized as random field. The probability of failure is obtained by numerical simulation, a particular critical slip surface is considered at each realization.
The research objective is to understand the effects of the soil spatial variability on the overall safety of pipelines laydown over hill-type imperfections. And pipelines susceptible to landslides.