Large deformation finite element analyses were carried out to investigate the optimized trench geometry for 24 inch (610 mm) diameter subsea pipelines and power cables (33 kV; outer diameter = 186 mm) used for transporting gas in shallow water depth (approximately 15 m), with an emphasis being on pipe-soil interaction assessment. An extensive parametric investigation was performed varying the relative density of the backfill sand (35%, 54% and 78%) and buried depth (1.89 and 3.14 diameters). Upward and lateral soil failure mec hanisms around a pipe uplifting in a backfill sand layer were compared. The failure mechanisms were manifested by shear band formation and subsequent propagation. It was shown that the trench dimensions originally designed based on conventional conservative approaches can be reduced by up to 10.6% in loose backfill sand (ID = 35%) and 8.7% in dense backfill sand (ID = 78%), leading to minimize cost and time of trenching and backfilling.

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