Numerical investigation on failure modes of bell-spigot jointed ductile iron pipelines subjected to dip-slip faults with different dip angles

Abstract

Effective identification of failure modes for buried pipes subjected to earthquake-induced fault movements is crucial in the design and assessment of underground water supply networks. For bell-spigot jointed ductile iron (DI) pipes, the relationship between pipe failure mode and dip angle is still unclear. In this study, a three-dimensional finite element model of buried DI pipelines crossing dip-slip faults perpendicularly is established, based on which the joint kinematics and mechanical responses of DI pipes subjected to dip-slip faults with a dip angle between 50° and 130° are systematically evaluated. Four failure modes controlling the joint sealing performance and structural integrity of DI pipes are identified, i.e., joint pull-out failure, joint rotation failure, joint compressive failure, and excessive local buckling in the pipe segment. The results reveal that joint self-locking induced by the action of horizontal compression can reduce the joint rotational capacity greatly, rendering a segmented pipeline to behave like a continuous pipeline. Upon the occurrence of joint self-locking, the pipe mode changes from kinematic-controlled failure (joint pull-out or rotation failure) to mechanical-controlled failure (joint compressive failure or excessive local buckling). Finally, the relationship between failure mode and allowable dip angle is derived for use in design.