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  1. Turning fines and soft (dredge) sediments (also so-called unsuitable) into a useful resource for climate resiliency (e.g. clay for dikes), nature development (e.g. nature islands), or sustainable human activities (e.g. land reclamation or industrial waste basin closure) is a critical opportunity for sustainable development, in the Netherlands and internationally (as demonstrated by ongoing projects such as Markerwadden, Kleirijperij, Surricates).

    In this project, two well-established constitutive models that describe the rate-dependent response of soft soils were extended by including the time-dependent thixotropic effect on the shear strength. The first constitutive model is developed in the framework of total stress analysis, which can capture the rate-dependency and thixotropy of the shear strength under the hypothesis of the undrained response of the system. The second constitutive model is developed in the framework of effective stress analysis and is able to take into account the contribution of pore pressure dissipation to the stability of the sand capping. The total stress thixotropic constitutive model was then used to perform large-strain numerical simulations of sand capping using MPM.

    A lab-scale test was successfully simulated, with good agreement between numerical simulations and experimental data at all loading stages (see figure below as an example of output). This is a breakthrough step towards bridging the gap between the “fluid mechanics” approach and the “porous media mechanics” approach for what concerns flow-like failure problems, such as extended flow failure behavior of soft sediments. This is particularly relevant for applications like sand capping and resulting potential slope instabilities. 

    The Sand Capping Construction. Lift 9. The red dotted line is the experimental observation.