Seismic behavior of buried PE pipelines subject to fault offsets

The paper presents the results of a series of centrifuge tests on the behavior of buried PE pipe subject to the fault offset hazard. The tests simulated both Strike-Slip (SS) and Normal offsets. Besides fault type, the three main parameters that were varied include the pipe burial depth, the intersection angle between the pipe axis and the fault (SS faults) and the direction of faulting (SS with right lateral or left lateral offset). Instrumentation allowed acquisition of pipe strain data which was decomposed into axial strain and flexural (bending) strain components. The paper will describe the rates at which strain decreases with distance from the fault, and the strong influence of burial depth and intersection angle on the magnitude of axial and flexural strain. New instrumentation allowed acquisition of the normal pressure between the buried PE pipe and the surrounding soil. As one might expect the normal pressure varied in the circumferential direction, as well as with distance from the fault. These pressures were used to estimate force-deformation characteristics of the equivalent 'soil-springs'. Unlike the 2-D behavior assumed for soil-spring models currently used in practice, the centrifuge results show that the behavior is actually 3-D in nature. Fortunately, as will be shown in the paper, 2-D soil-spring models yield conservative results in terms of pipe strains.