Large-scale physical modelling of static liquefaction in gentle submarine slopes

Arash Maghsoudloo,Frans Molenkamp,Richard R De Jager,Amin Askarinejad,Michael A Hicks

doi:10.1007/s10346-021-01705-6

Abstract

Planning a monitoring campaign for a natural submarine slope prone to static liquefaction is a challenging task due to the sudden nature of flow slides. Therefore, gaining a better insight by monitoring the changes in pore pressure and acceleration of the soil mass, prior to and at the onset of static liquefaction, of submerged model slopes in the laboratory, helps in quantifying the minimum required triggering levels and ultimately the development of effective margins of safety for this specific failure mechanism. This study presents a set of physical model tests of submarine flow slides in the large-scale GeoTank (GT) of Delft University of Technology, in which a tilting mechanism was employed to trigger static liquefaction in loosely packed sand layers. Novel sensors were developed to locally monitor the hydro-mechanical soil responses acting as precursors of the onset of instability. The measurements indicated that soil instability can initiate at overly gentle slope angles (6–10°) and generate significant excess pore water pressures that intensify the deformations to form a flow slide. Moreover, it was observed that the onset of instability and its propagation are highly dependent on the rate of shear stress change and the state of the soil. The obtained data can be used for the future validation of numerical models for submarine flow slides.

Highlights

Flow slides have been classified as one of the types of submarine mass movement (Locat 2001), and they are amongst the most common types of failure of submerged slopes in deltaic areas (Koppejan et al 1948; Kramer 1988; Lade and Yamamuro 2012; De Groot et al 2019)
The nature of submarine slides by the static liquefaction of bulk volumes of very loose sand often leads to catastrophic dynamic failures which depend on the slope geometry and triggering intensity
Summary and conclusions The main objective of the presented research was to understand the instability mechanism of submarine slopes composed of loose sand and to examine the fundamental contributing factors to failure, such as the rate of change of the destabilising loads and the packing state of the soil

Summary

Introduction

Flow slides have been classified as one of the types of submarine mass movement (Locat 2001), and they are amongst the most common types of failure of submerged slopes in deltaic areas (Koppejan et al 1948; Kramer 1988; Lade and Yamamuro 2012; De Groot et al 2019). Several researchers have listed contributing factors in the triggering of submarine flow slides (Kramer 1988; Hicks and Boughrarou 1998; Sassa and Sekiguchi 2001; Miyamoto et al 2004; Hicks and Onisiphorou 2005; Masson et al 2006; Lade and Yamamuro 2011; Sumer 2014) These include wave actions, scouring, water currents, sea level changes, soil variability, seismic loads, and construction loads (e.g. loading during the construction of hydraulic fills and unloading and imposed pressure variations during dredging). The resulting flow slides involve potentially large liquefied bulk volumes flowing over large distances and potentially induce tsunami-like phenomena Such failures may be contrasted with the progressive nature of failures in denser sands, which often involve stable propagating retrogressive shear bands in combination with simultaneous pore water seepage for redistributing excess pore pressures (Puzrin et al 2015; Zhang et al 2017)

Objectives

Discussion

Conclusion