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.

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Static liquefaction is one of the principal triggering mechanisms of failure in fully saturated loose sand slopes both in offshore and onshore regions. Static liquefaction induced landslides are known for their significant softening and a fluid-like behavior at the onset of failure. However, the literature lacks experimentally verified advanced numerical approaches which are capable of simulating static liquefaction. In this study, an advanced constitutive model based on the multilaminate framework is used in a finite element code. Multilaminate model accounts for significant features such as rotation of principal stresses, anisotropy in the material, strain softening due to static liquefaction and stress and strain dependency of the stiffness which enable us to achieve a more realistic soil behavior. The analysis results are verified by a set of large scale experiments of static liquefaction failures in submerged slopes under monotonic loading. Presented numerical approach can be used as a tool for further investigations of static liquefaction induced flow slides. This is useful for design and optimization of static liquefaction mitigation techniques.@en

The liquefaction tank is an experimental facility developed to conduct physical scale model tests of liquefaction flow slides. We developed the liquefaction tank to evaluate the performance of advanced numerical models for submerged slopes composed of sand. For the long-term, the research with the liquefaction tank aims at composing a database with high-quality experimental results of liquefaction flow slides, in which properties related to the soil, degree of saturation, geometry, triggering and mitigating measures will be varied.
This paper addresses the first results obtained with the liquefaction tank. We used a fluidization system to create a uniform, loosely packed sand bed. The liquefaction tank was subsequently tilted uniformly, while measuring the pore pressures at the base of the sand bed. Furthermore, the stability of the slope was monitored using a camera system pointed at the transparent side of the tank. We conducted around 30 tilting tests on a level sand bed while varying consolidation time, density and tilting rate.
We were able to reproduce liquefaction flow slides below a particular threshold density. The moment of failure was noted by an instant, uniform liquefaction of the sand bed, preceded by an abrupt increase of excess pore pressures. The results in terms of failure angle and measured pore pressures were consistent and reproducible. The measured failure angle was much lower than anticipated from results of element tests in literature. Future research aims at relating the results to the response during undrained triaxial tests and the effect of mitigating measures.
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