Upheaval Buckling Resistance of Pipelines Buried in Unsaturated Clay Backfills

High pressure and high temperature (HPHT) oil and gas pipelines, the burial depths of which are determined by the mitigation requirement of upheaval buckling deformation or legislation requirement, are commonly buried below the ground surface. Uplift resistance of soils surrounding the buried pipeline should be considered into the design of upheaval buckling behavior. Conventional design guidelines and current analytical models based on either dry soil or fully saturated soil are generally applied to predict the soil uplift resistance behavior. Therefore, the HPHT pipelines are mostly buried in unsaturated onshore soils. This paper presents a series of small pipe-soil interaction experiments for measuring the reaction that is acted on the buried pipelines in unsaturated backfill soils, and its purpose is studied to evaluate the impacts of soil moisture content, pipeline burial depths, and tension loading levels on the soil uplift resistance behavior. A new simplified formula based on the uplift experiment results is specially established to predict the uplift resistance of soils. Further, the uplift failure mechanism and pipe-soil interaction behavior are effectively applied to predict the upheaval buckling behavior of the pipelines buried in unsaturated soils.