On the potential of gassy marine soils triggering submarine slope instabilities

Pauline Kaminski,Jürgen Grabe

doi:10.1051/e3sconf/202020512006

Abstract

The development of debris flows and turbidity currents in the course of a submarine slope failure event can cause major damage in offshore infrastructure. Additionally, the tsunamogenic potential of large slope failures at continental margins poses a direct threat to coastal communities. Therefore, the trigger mechanisms of submarine slope failures have been thoroughly investigated in the past. However, the influence of free gas in the sediment, which has been observed close to several slide events, remains unexplained. In order to evaluate the potential of gassy marine soils to precondition or trigger slope failure the mechanical behaviour of gassy soils is assessed based on an extensive literature review. It is found that gas-induced excess pore pressures can lead to liquefaction failure in sands, while cohesive, gassy soils show a less conclusive response. Hence, fine-grained soils and approaches to implement the gas impact into relevant existing constitutive soil models are assessed in greater detail. Concludingly, based on the predominant boundary conditions in failure prone regions at the continental margins, free gas occurrence can be defined as a preconditioning factor rather than as a definite trigger mechanism.

Highlights

The exploitation of energetic resources in the offshore areas has been successfully conducted in the past years, forwarding into deeper waters in the recent years
The tsunamogenic potential of large slope failures at continental margins poses a direct threat to coastal communities
In order to evaluate the potential of gassy marine soils to precondition or trigger slope failure the mechanical behaviour of gassy soils is assessed based on an extensive literature review

Summary

Introduction

The exploitation of energetic resources in the offshore areas has been successfully conducted in the past years, forwarding into deeper waters in the recent years. Leaving the shelf seas and approaching the continental slopes stability assessments of the latter become relevant [1]. The occurrence of marine gases has been linked to several investigated slide events [5,6]. Possible approaches to assess the hazardous potential of marine gassy sediments are given. These include theoretical models of geomechanical processes in gassy soil. Approaches to include the gas phase, or rather the gases impact, in constitutive models in order to make a numerical assessment of gassy soils possible are discussed. The impact of a free gas phase on the overall stability of a slope requires further consideration in combination with other weakening factors

Submarine landslides and gas occurrence

Gassy soil mechanics

Constitutive modelling

Findings

Conclusion