Lateral load-displacement behaviour of pipelines in unsaturated sands

Conventional design guidelines for buried pipelines are based on the assumption that soil is either dry or fully saturated. In unsaturated soils, such an assumption may lead to underestimation of load from externally imposed ground movement. Such loads are generated because the water meniscus between soil particles creates an additional inter-particle force due to suction, which in turn makes the soil stiffer and stronger. This paper presents a methodology for predicting lateral loads on pipelines in unsaturated sandy soils by investigating soil-pipe interaction with full-scale tests and characterizing unsaturated soil behaviour with properties from triaxial tests. A constitutive model was developed, and finite element (FE) simulations were performed and compared with the full-scale test results to validate the modelling process. Additional FE simulations were conducted to assess the maximum lateral load on pipelines buried in different Class II (ASTM, 2011) unsaturated sands. The full-scale tests and FE simulations show that increased strength and stiffness associated with soil suction increases lateral loads on pipelines and thus needs to be considered when designing pipelines for externally imposed ground movement. The modelling procedures and results can be used to predict lateral loads on underground pipelines subjected to construction and earthquake-induced ground movements, landslides, and subsidence. Because most pipelines are buried in unsaturated soil, the results have widespread relevance in design and construction.