Undrained bearing capacity of skids/pedrails during trenching for buried submarine pipelines

Abstract

The paper investigates the undrained bearing capacity of an underwater trencher used for installation of buried submarine pipelines. The underlying soil is assumed to have an undrained strength that increases linearly with depth. The paper presents charts for the bearing capacity of these systems as a function of trench geometry, loading distance (i.e., the distance between the trencher skid/pedrail and the crest of trench wall), surface strength and the gradient of strength increasing with depth. These charts can guide engineers in the level of buoyancy needed for safe trenching operations. All calculations are performed using finite element limit analysis (FELA) and the parametric studies reveal five principal failure modes. At last, the paper includes an engineering example to demonstrate the use of the charts for practice.