Response of buried pipelines to repeated shaking in liquefiable soils through model tests

Liquefaction hazard induced by seismic events might affect the stability of buried pipelines, with permanent displacements of the embedded structure as a consequence. In this context, the pipe uplift is of main concern, as already widely discussed in the literature. In this paper, further insights to assess the phenomenon and the related effects on pipelines are provided based on the results of shaking table tests on pipes of different apparent unit weight. A multiple shaking sequence is adopted on each model. Among others, data here reported confirms that, with liquefaction occurrence, upward displacement is expected for a pipe with an apparent unit weight smaller or equal to the unit weight of the sand deposit; the opposite for larger apparent unit weight. The pipe vertical displacement is initiated with the first earthquake that in sequence induces liquefaction extensively in the soil deposit. The uplift rate is higher for this shaking, and then it reduces for the next earthquakes even for bigger shaking amplitude. The onset of uplift varies for successive earthquakes depending on the magnitude of the input motion, the relative density and the weight of the structure. A transient horizontal movement of the transversal cross section of the pipe, due to the earthquake loading inducing liquefaction in the soil deposit, can be significant and induce pipe damages.