Trench Effects on Pipe-Soil Interaction

Trenched pipelines subjected to large lateral soil movements were studied to quantify mitigative effects of trench geometry, backfill soil material and strength on the force-displacement behaviour in cohesive soils. Experimental and numerical models show a good agreement in terms of undrained ultimate forces, which are also consistent with design guidelines and previous studies. Undrained lateral pipe resistance factors, are assessed in terms of soil strength and soil weight in uniform soil. A normalised pipe displacement rate characterizes a transition in the lateral resistance from undrained to drained conditions is presented. The presence of a trench backfilled with material weaker than the native soil softens the lateral load-deformation (p-y) response compared to that of the same pipe buried in native soil. An increase in the trench width increases the pipe displacement to peak load. The lateral interaction force is much lower in a pipe with a wider trench than a narrower trench prior to reaching the peak load. The peak load occurs after pipe touches the trench wall and is controlled by the native soil strength. It decreases slightly with increase in the trench width because of upward movement of pipe prior to reaching trench wall. The mitigative effects of trench wall inclination are also demonstrated. A simple approach to determine the p-y response for a trenched pipeline backfilled with material weaker than the native soil is proposed.