Real scale test design of a sand flowslide by MPM slope (in)stability analysis

Description

Session III: Advanced numerical modelling of geomaterials with
emphasis on large deformation and flow problems

Abstract: The ability to predict sand flowslides is an important asset for the design of submerged slopes, their construction, maintenance and safety assessment; even more so in view of intensifying land use and the impact of sea level change on low-lying coastal areas worldwide. However these phenomena are not yet well understood. It is convenient to further distinguish between liquefaction and breaching types of failure (Sadrekarimi 2014, Van den Berg 2002, and Figure 1). The failure mechanism depends on the dilatative or compactive behavior of sheared sand. The study of sand flowslides requires an integrated approach of fluid and soil mechanics: soil movement induces turbulent water motion which in turn interacts with the eroding soil surface. Currently, such an integrated approach is lacking. Studies so far mostly rely on empirical approaches that apply to specific circumstances only and use considerable simplifications. Furthermore, empirical solutions on erosion and sedimentation fall short in sufficiently capturing these interacting processes. As an alternative, physical experiments involve high costs as scale effects necessitate large test facilities and such tests often only allow predictions for specific projects. This makes the safety assessment of submerged slopes and the development of measures to prevent sand flowslides difficult and expensive. Sand flowslides are considered highly complex (multi-phase, multi-physics and multi-scale) and the use of numerical methods for the solution of these problems play a key role for the optimization and the design of many projects.

An integrated numerical solution for the simulation of sand flowslides from initiation up to deposition of sediments is being developed using the MPM software Anura3D. This software is in an early development stage and validation and implementation activities are necessary to make it suitable for civil engineering applications. The design procedure of a real scale test will be described and the numerical model alternatives (Figure 2) for the validation of the Anura3D MPM software for slope (in)stability analysis. The results from the numerical models support the assessment of the expected type of failure. Based on the retrogressive pattern of the failure, the location and sensitivity of the sensors will be selected. In fact, there is no complete dataset in literature describing and analyzing the initiation (triggering mechanism), the onset (suspended sand flow resembling the motion of viscous liquids) and deposition (final geometry) for a sand flowslide. In order to monitor the onset of the sand flowslide, an innovative monitoring technique is here used: instrumented Lagrangian particles (SmartINST). The site is characterized and the constitutive models are calibrated for the advanced numerical method. Because of the large range of stresses and strains involved in the phenomena, the constitutive relation to model the soil water mixture should include critical state soil mechanics and features of dense saturated undrained sand. A hypoplastic constitutive model is therefore here selected (Wolffersdorff 1996). The chosen site for the real scale test is a sand quarry below the water table in Belgium and the slope failure will be triggered by excavating the toe of the slope with a dredging machine (Figure 3).

Period	2 Oct 2017 → 7 Oct 2017
Event title	28th ALERT Workshop and School
Event type	Workshop
Location	Aussois, FranceShow on map
Degree of Recognition	International