Influence of random soil strength properties on the earthquake vulnerability of slopes with embedded oil and natural gas pipelines

Abstract

Numerous pipeline systems carrying oil and natural gas, passing through geologically unstable areas worldwide are vulnerable to seismically induced slope instability, large ground displacements and settlements. Such ground movements constitute significant obstacles towards achieving certain standards for the pipeline concerning both safety and structural integrity, as well as conformity to safety rules regarding environmental safety in case of wall rupture and loss of containment. The two-dimensional distribution as well as the intensity of the subsequent ground movement could significantly depend on the two-dimensional mutability of soil properties in an area alongside the pipeline system. This paper aims at rationally accounting for the effects of the two-dimensional mutability of soil properties on the seismic performance of interred oil and natural gas conduits passing through natural slopes. More specifically, the effects of two-dimensional mutability of soil properties, slope inclination and earthquake excitation characteristics on the development of permanent displacements are investigated using random fields created by the Local Average Subdivision method by Fenton and Vanmarcke (J Eng Mech 116(8):1733–1749, 1990). These random fields of soil properties are characterized by specific mean, variance, cross-correlation coefficients and autocorrelation lengths and used for performing a series of seismic analyses of various slopes by utilizing the FLAC software to calculate finite difference through a Monte Carlo type simulation methodology. The outcomes of an all-encompassing parametric inquiry allow the development of vulnerability curves, based on the permanent horizontal or resultant displacement for several seismic intensity levels. Findings clearly show that the influence two-dimensional mutability has on soil properties on the ground movement imposed on the embedded pipeline are very important and should be accounted for in the evaluation of its seismic safety.