Long-term response of flexible pipe in sand trench due to consolidation of native clay

The finite element analysis are performed to investigate a long-term response of flexible pipe buried in sand trench embedded in native soft clay. The investigated long-term behaviors are due to effects of backfill soil structure rearrangement and native clay consolidation. The finite element results suggest that the short-term response of pipe depends strongly on trench widths but independent of trench depths due to the dependence of arching effect with trench width. However, the effects of trench width become less important for long-term pipe response. Moreover, the mechanism of this long-term response is likely due to backfill soil structure rearrangement, which occurs within a shorter time, not consolidation of native clay. The importance of finite element modelling of interface between sand backfill and clay trench and modelling of construction sequence on the obtained pipe-soil interaction are investigated. For long-term consideration, modelling of interface between sand backfill and clay trench is important; however, modelling of construction sequences is not so. Prism load seems to give better results for long-term load. Available analytical solutions cannot accurately estimate both vertical load and pipe deflection at short term for narrow trench due to a strong influence of arching effect after backfilling. At long term, Iowa formula under-predicts the horizontal pipe deflection by the ratios of 0.40–0.52 which correspond with a deflection lag factor DL of 1.9–2.5. The time lags of narrow trench obtained from this study are 1.6–1.9 and they become smaller for wide trench