Experimental identification of stiffness and ultimate resistance of buried soil-pipe systems

In context of pipeline design, the soil’s stiffness and ultimate lateral resistance are critical values. Existing approximations for ultimate lateral resistance vary significantly and there are few expressions for the soil stiffness parameters. These parameters are implemented in soil constitutive models for pipeline design under different displacement induced conditions. This research focusses on the experimental investigation of the response of the soil-pipe system to enforced horizontal loading for application to natural gas pipelines. The study examines shallow burial depths (<5.5D), using a section of solid acrylic pipe in dry Leighton Buzzard grade B sand. Plane-strain conditions have been replicated and experiments run to evaluate quantities for soil stiffness, through lab experiments and validated finite element analyses (FEA). Monotonic loading was applied onto the pipe within varied conditions, changing both burial depth and soil density to establish the relationship with soil stiffness. The FEA results were used to ratify such behaviors, establishing an analysis for displacement response and corresponding stiffness parameters. Absolute and relative stiffness values from both analyses were then compared with existing literature and the results reflect the importance of relative soil properties and expected displacements. Results find that horizontal loading within shallow burial depths induce 2D displacements, which could be modelled as vectors rather than horizontal displacements.