Numerical and Experimental Study of Uplift Mobilization of Buried Pipelines in Sands

Abstract

Offshore oil and gas pipelines are commonly buried in seabed to provide environmental stability, thermal insulation and mechanical protection. These pipelines are frequently subjected to high thermal and pressure loadings that induce pipeline upheaval buckling (UHB). The uplift resistance provided by the cover soil increases with pipeline upward mobilization and reaches its peak at peak mobilization. This peak mobilization is fundamental for safe UHB designs. This paper highlights that the design guidelines underestimate the peak mobilization. The paper presents full-scale uplift results and finite-element parametric studies in which loose and dense cover soils of up to 3 m (soil cover height to diameter ratio up to 15) and pipeline diameters of 114 and 200 mm were investigated. Results from full-scale and finite-element modeling show that the peak pipe mobilization can be much greater than that suggested by current guidelines, and it is a function of the soil cover height to diameter ratio and soil relative density. A new relationship is proposed to predict peak mobilization from the soil cover height to diameter ratio for a given soil state.