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Deltares | R&D Highlights 2015 Delta Infrastructure
Water affects the safety of houses, industrial buildings and public infrastructures located in coastal areas and on river banks, as is seen in various ways: erosion, scouring, flooding or wave attack, for example. These phenomena can seriously damage engineering structures, with catastrophic consequences. One approach to investigating soil-water interaction problems is to perform physical experiments. However, some phenomena like erosion cannot be reproduced accurately on a small scale. As an alternative, powerful computers and computational mechanics provide opportunities to simulate these problems using numerical modelling. The modelling of soil-water interaction focuses on the numerical modelling of the complex behaviour of soils, water, and mixtures of the two when subjected to large deformation processes. The response of the soil-water mixture varies significantly depending on its state. The soil-water mixture can behave as a soil body (this is the typical assumption in classical geotechnical engineering) or as a fluidised mixture in which solid grains are transported in water and deposited as sediments. The behaviour is also affected by water flowing through the soil body due to the interaction of water and the solid skeleton resulting in drag forces.
Although numerical models of computational fluid dynamics (CFD) are appropriate for sediment flow and deposition, they are less suitable for the study of the mechanical response of soil during and after the sedimentation process. Deltares therefore developed a new numerical tool with the University of Cambridge as part of the European Project MPM-Dredge. This new tool uses the Material Point Method (MPM) and allows for the simulation of large deformation problems involving soil, water and the interaction between them. For this particular application - the simulation of the behaviour of free water, soil and the transition between fluidised and non-fluidised states - two sets of material points were introduced. The first set describes the physical
behaviour of the liquid constituent and the second set describes the response of the solid.
Several problems were successfully simulated and used as benchmarks in the present project. Situations with analytical solutions (seepage flow through a soil body, for example) and more complex examples (complete state transition) were both investigated. The free fall of coarse-grained soil under water clearly showed that the fluidisation and sedimentation processes are well described and correspond to physical expectations. In another example, the collapse of a submerged soil column was modelled using two different initial soil densities. In the dense soil case, breaching was observed; in the loose soil case, full liquefaction occurred. These two cases demonstrate the importance and feasibility of taking the constitutive soil model and large deformations into account. Finally, the failure of a dike due to seepage was simulated. Not only the failure mechanism of the dike but also the subsequent sediment transport were reproduced using MPM.
In the future, this new MPM approach will facilitate the modelling of the soil-water interaction, allowing engineers to design solutions to mitigate associated risks and to improve the construction process in industry. For example, it will be possible to model the full installation process for geocontainers, during which they are subjected to large strains and cyclic deformation. Their high permeability allows the water to flow not only around the container but also through the geomaterial itself. Soil liquefaction, fluidisation and sedimentation are some of the phenomena that occur during a catastrophic failure of this kind and that can be taken into account in this new MPM approach. Finally, in the future, MPM simulations can be used as a support tool for the construction of a hydraulic-fill tailings dam in the mining industry.
Collapse of submerged sand column
Free fall of coarse-grained soil under water
Collapse of a soil slope due to seepage mario.martinelli@deltares.nl
T +31(0)88 335 7210 alex.rohe@deltares.nl
T +31(0)88 335 7351
Modelling of soil-water
interaction
Free fall of coarse-grained soil
