Soil Responses to Monotonic and Cyclic Lateral Displacement of a Buried Pipe

Soil resistance to monotonic lateral displacement of buried pipelines has been well studied in the literature, but there is limited information on the interaction between soil and buried pipes subjected to cyclic displacement. A new full-scale testing facility was built to investigate the cyclic interaction behavior between soil and buried pipes for a potential onshore application, in which hydrocarbons can be transported at high pressure and temperature inside large, heavy, steel pipes. A full-scale experimental program was conducted for a 1.2-m-long pipe segment buried under gravel backfills. The pipe segment was subjected to lateral displacement with a series of combined monotonic and cyclic loading protocols. Two parameters were studied in the tests: embedment depths and compaction levels of backfill materials. It was observed that for the gravel backfill, the ultimate displacement could far exceed the expected range specified in the design guideline, and while the ultimate soil resistance to the monotonic loading can be predicted, the ultimate resistance could increase as high as 150% of the value of the monotonic loading case due to the applied cyclic displacement. This increase in the ultimate resistance depended on both the soil compaction and the cyclic loading history.