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.

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.

In order to verify the capability of finite element models with the constitutive model MONOT (Molenkamp, 1980) to predict both the initiation of liquefaction of a slope of loose sand and the initial flow pattern a series of liquefaction tests in the BRUTUS-tank at Delft Geotechnics has been proposed (Molenkamp, 1982).