Effects of gravel layer as thrust restraint for pipe bends subjected to earthquake loading

This paper reports effects of gravel layers as a thrust restraint in a pipe bend subjected to earthquake loading based on the shaking table tests in a centrifuge. The model pipe was buried under four backfill conditions differing in the existence and layout of a gravel layer. The pipe was pulled laterally with a constant load, simulating the thrust force generated at bends in pressure pipelines with diameters of 1800 mm. Shakings were conducted on the model pipe with lateral loading. The test results showed that the gravel surrounding the pipe was effective as a thrust restraint for pipes of large diameter. A gravel layer on the passive side was found to be particularly crucial. A gravel layer on the active side provided no thrust-restraint effect, although it did reduce pipe displacement amplitude. A gravel layer on the upper half of the passive side of the pipe likely contributed to mitigation not only of lateral displacement but also of pipe uplift.