Abstract

Pipelines used for the transport of energy and services are very important lifelines to modern society. The vital role that they play in our present economy is reflected in the many kilometres of pipelines laid in onshore and offshore locations worldwide. They are often buried in the ground which provides protection and support, but ground movements can induce unwanted loading on the pipelines.

Although the pipelines generally buried in unsaturated soils, pipeline design guidelines are based on the assumption that the soil is either dry or fully saturated. For many years, the mechanical behaviour of unsaturated soils was either ignored or approached inappropriately by using the traditional framework of saturated soil mechanics. For certain geotechnical problems, it may not be acceptable to have such assumptions because the meniscus formed between soil particles creates an additional normal force between the particles by suction, which in turn forms temporary bonds. A recent series of large-scale physical model experiments in the Pipeline Engineering Research Laboratory of Tokyo Gas, Japan, show a higher peak load under unsaturated conditions compared to dry conditions. In contrast, other recent experiments performed at Cornell University show that the soil-loads by lateral pipeline movement in dry and unsaturated sands are virtually the same. Thus, the effect of partial saturation on soil loading to pipeline may be different depending on soil type, moisture condition and density. The current study investigates this problem through constitutive modelling of the unsaturated soils used for testing and finite element analysis of soil-pipeline interactions in unsaturated soils.