Envelopes for the soil-resistance capacity of a shallowly embedded pipeline in clay under three-dimensional combined loadings

Envelopes are developed for the soil-resistance capacity of pipelines shallowly embedded in clay subjected to combined three-dimensional vertical (V), horizontal (H) and axial (T) loading. A three-dimensional pipe-soil interface is developed to account for the effect of tension and separation between the pipeline and soil, which is used in numerical finite element modelling. Each of the 1800 finite element analyses defined a unique V-H-T condition causing failure of the soil around the pipe for a variety of pipe embedment. Using these results, a closed-form mathematical expression expresses the capacity envelope of the soil resistance to the pipe under three-dimensional V-H-T loading that is only a function of the pipeline embedment and the tension at the pipe-soil interface. Offshore pipeline engineers can use this expression to estimate the soil resistance under combined three-dimensional loading in their assessment of the stability and integrity of offshore pipelines.