Finite element simulation of seismically induced retrogressive failure of submarine slopes

Abstract

Retrogressive failures have been reported for both offshore and onshore slopes subjected to various triggering mechanisms. As a result of large spatial extension of the failure, the retrogression phenomenon leads to significantly increasing damage and may affect facilities located far away from the original slope. The mechanisms of such failures are not fully understood, and reports of analyses are rather scarce. To simulate earthquake-induced retrogressive submarine slope failures and to better understand the mechanisms involved, the element removal capabilities of a finite element program are used to model a soil mass that fails and then flows away, causing upper parts of the slope to fail retrogressively, as a result of the loss of support. It is explained how an initial failure leads to subsequent failures of a flat seafloor. Effects of a shallow silt layer and of a gently sloping seafloor on the extension of retrogression in a sandy seabed are also studied. It is found that the extension of failure increases significantly because of a gentle seafloor slope and (or) the presence of a silt layer.Key words: retrogressive submarine failure, seismic liquefaction, finite elements.