Axial Resistance in Shallow Buried and Deep Buried Pipelines Subjected to Ground Deformation

Axial resistance of a buried pipe depends on several factors, including pipe-soil interface behavior, actual displacement pattern of the pipe-soil interface, configuration of the pipe segments and joints, any available axial flexibility within pipe joints, and burial depth. Traditionally, axial resistance in buried pipes is estimated using frictional and adhesive behaviors of the pipe-soil interface of the pipe barrel without considering any additional axial resistance contributions arising from enlarged portions of the pipe joints and dilatant behavior of the soil. Additional axial and passive resistance contributions from the enlarged pipe joint configuration and increased normal pressure distribution resulting from the dilatant behavior of the soil can be significant axial resistance that is normally tacitly neglected. Axial resistance using these simplifications gives a reasonable estimate of axial resistance for buried pipelines with uniform pipe barrels; however, this approach significantly underpredicts axial resistance for buried pipelines with enlarged joint configurations and pipelines constructed within dense granular soils. While the use of underestimated axial resistance for traditional non-seismic situations (e.g., thrust restraint design problems) mostly yields conservative designs, such is not the case for seismic design conditions. Especially important is the axial resistance contribution in estimating the connection force demand arising from potential seismic hazards acting on a pipeline. Recognizing the importance of accurate estimation of the axial force connection demand on a buried pipeline from a design seismic hazard, experimental and theoretical studies have attempted to develop proposed approaches to estimate the axial resistance of a buried pipeline. The author has previously developed equations to estimate the maximum axial resistance of a deep buried pipeline, assuming shallow passive failure mode is not probable. This paper presents updated equations for axial resistance of a buried pipeline considering passive and active pressure contributions from both shallow buried and deep buried pipelines. In addition, this paper also provides comparisons of the axial resistance estimates from the proposed formulations and results from available experimental studies performed by others to validate the proposed formulation.