How to Accommodate Differential Settlement Using Geohazard Resistant Steel Pipe

Quite often, buried pipelines connected to rigid structures or existing buried pipelines undergo differential settlements that, in addition to stress and strain from normal operational conditions, may impose significant stress and strain in the pipe wall. The pipeline should be capable of accommodating the imposed displacement due to settlement while maintaining its structural integrity and fulfilling its water transmission function without leaks. Currently, the use of couplings or joints that depend on gasket seating to maintain water containment after settlement is the typical solution for lesser amounts of differential settlement. The paper describes the expanded application of the engineered steel pipe solution identified as Geohazard Resistant Steel Pipe (GRSP) for use in differential settlement applications. The application of GRSP for absorption of ground displacement in a controlled and efficient manner allows for fully welded joints, eliminating the need for gaskets. GRSP has been introduced in previous ASCE Pipelines conferences and validated with a series of full-size physical tests backed with extensive rigorous finite element simulations. It was shown that GRSP can be used in seismic or ground fault areas where ground-induced actions are expected to occur. GRSP has also been applied in settlement or subsidence areas, offering a simple and economical solution for absorbing the deformation imposed by differential settlement or subsidence. This paper will provide design guidelines and design tables on the use of GRSP and, specifically the InfraShield Joint System (IJS), patent pending. The design tables and design guidelines are developed from the full-scale testing on 24-in.-diameter pipes and continued with extensive finite element (FE) simulations on 84-in.-diameter pipes under differential settlements. This paper will expand on this FE work and include 42-in. and 24-in.-diameter pipe simulations. Two primary cases are considered: (1) the soil settles, causing pipeline deformation, whereas the nearby structural system has negligible settlement, and (2) the structural system settles, while the soil next to it exhibits negligible settlement. The main parameters for the advanced FE work are: (1) soil types (stiffness); (2) diameter-to-thickness ratio ( D/t); (3) level of internal pressure; (4) size of soil cover above the pipeline; and (5) amount of vertical or horizontal settlement. Using the results of these extensive studies, application tables for settlements of up to 4 in. for diameters of 24 in. through 96 in. are provided, accompanied by design and GRSP installation guidelines.