Soil Behaviour and Constitutive Modeling

The section historically has a very strong basis in fundamental soil mechanics. At the moment the section is developing new facilities to test fibrous materials to study the electrical and geomechanical properties of peat, and a unique direct simple shear/axial shear device for measuring the anisotropic behaviour of peat accounting for both the average orientation of fibres and very low stress levels. Moreover, a major new “tank” testing facility for investigating underwater slope liquefaction has been designed and constructed, funded by STW. The research includes the development of a novel triaxial apparatus to measure material properties at very low stress levels, and the development and implementation of advanced (state-parameter-dependent) constitutive relationships within a dynamic finite element code for the purpose of assessing liquefaction potential at larger scales. The tank is a crucial asset in future PhD research relating to current national concerns regarding the numerous historical and recent large underwater liquefaction slides that have occurred near the Oosterschelde storm surge barrier. Other possible application areas are landslides and the development of new types of site instrumentation. Future research will be linked to further constitutive model developments, as well as to numerical research using the Random Finite Element and Material Point Methods.

Axial shear device for testing fibrous soils (left) and liquefaction tank under construction (right).

New experimental research, funded by Shell, includes the development of a strategy for the enhanced dewatering of soft sediments to improve soil strength, focusing on dewatering techniques and the modelling of this process. This is relevant for the management of mine tailings, oil sands and deposits of dredging sludge, and for their application as alternative building materials. Meanwhile, numerical research on ground improvement by electro-osmosis has resulted in the development of a fully coupled formulation incorporating large deformations, elastoplasticity and nonlinear variations in soil transport parameters. This has been used to demonstrate efficiency gains possible with current intermittence, current reversal and various multiple electrode configurations, and is expected to be linked with future experimental research into improving embankment stability.

The section has also conducted a series of small-, medium- and large-scale experiments on backward erosion piping in collaboration with Deltares and the University of Ghent. This research investigated the conditions needed for the initiation and progression of piping beneath dykes; in particular, it highlighted limitations in the existing standard analysis used in design and developed a new improved method applicable to a wider range of sand types.