## 1 Introduction  
Pipelines are commonly used as the primary means for transmission of hydrocarbon fluids in the energy industry, and for transportation of water resources in the public utility industry. Previous investigations into the main causes of damages and loss of mechanical and structural integrity in pipelines have highlighted the detrimental impacts of geological conditions or environmental actions associated with various time-dependent thermomechanical phenomena, such as ground subsidence, soil liquefaction and land sliding, discontinuous frost heave/ or thaw settlement, fault movement due to seismic action, etc. [1; 2; 3]. Large displacements tend to induce significant strains in the wall of pipe segments, which may ultimately result in the failure of a pipeline either due to tensile rupture, especially at welded regions, or due to bulging or wrinkling deformation of the pipe under the influence of compressive stresses [4; 5; 6]. As a result of the inevitable requirement for pipelines to traverse large geographical areas, a majority of pipelines in the onshore energy and public utility industry are installed below the soil surface. It is observed that, compared to above-ground pipelines, the mechanical behavior of buried pipelines is significantly influenced by the geophysical properties of the surrounding soil. Hence, the intricacies of the mutual interaction between the pipe and the surrounding soil are regarded as an important consideration in the design of buried continuous pipelines [7; 8; 9; 10]. The common consequence of ground movement and thermal buckling deformation on pipelines is the experience of high longitudinal stresses and strains. Conventional pipeline design procedures are generally based on an _\"allowable stress\"_ concept, which aims to limit the resultant longitudinal and circumferential stresses in pipelines, either due to load-controlled or displacement-controlled conditions, to a prescribed fraction of the specified minimum yield strength (SMYS) of the pipe material. Unfortunately, the allowable stress design (ASD) approach tends to be severely limited by its inability to distinguish between stable and unstable failure modes, as well as between loss of serviceability and loss of containment [11]. A strain-based design (SBD) approach has therefore been regarded as more appropriate, and has been recently more adopted by various pipeline design standards (e.g., API RP 1111 [12], DNV-OS-F101 [13], ABS 2006 [14], CSA Z-662 [15]) for design of pipelines expected to experience high longitudinal strains caused by displacement-controlled environmental and operational conditions in service [16; 17]. SBD circumvents the inherent conservativeness of the ASD approach by permitting a limited amount of plastic strain, while maintaining relevant ultimate and serviceability limit state considerations. However, rather than consider the SBD and ASD approaches as independent techniques, best design practice recommends the application of SBD as a complementary tool to the more traditional ASD procedure [18]. SBD employs a limit state design approach, whereby the in-service longitudinal tensile or compressive strain that a pipeline is expected to experience due to displacement-controlled loading conditions (i.e., strain demand) is evaluated and compared to the tolerable limit of strain which the pipeline has intrinsic ability to withstand (i.e., strain capacity). Estimation of strain demand in pipelines typically involves a rigorous and often complex process, which requires all-inclusive consideration of numerous interrelating factors related to various environmental and geological conditions, and the pipe's mechanical properties. The strain demand is also highly dependent on a number of peculiar, and sometimes transient, environmental conditions, making the development of deterministic prediction models difficult, and often necessitating the use of probabilistic and reliability-based estimation techniques for the SBD [19; 20].