Numerical Modeling Procedures for Consolidation of Fine-Grained Materials in Geotextile Tubes: Fid-Bau Portal

Numerical Modeling Procedures for Consolidation of Fine-Grained Materials in Geotextile Tubes

Brink, Nicholas / Kim, Hyeong-Joo / Znidarcic, Dobroslav

Self-weight consolidation of fine-grained soils has been studied intensively for several decades, beginning with the development of finite strain consolidation theory. Several geotechnical design scenarios require accurate prediction of these self-weight consolidation processes, though few tools are presently available. It is the goal of this research to develop numerical modeling procedures for implementation in commercial finite element codes which will allow engineers to readily predict the consolidation of very soft, fine-grained soil slurries. A primary focus of this research is on the modeling of the consolidation of geotextile tubes filled with fine-grained soils. Fine-grained fills are commonly encountered in the mining industry, where geotextile tubes are used to confine and dewater fine-grained tailing. Scenarios such as this one require an accurate prediction of the consolidation behavior of soil slurries. Numerical modeling techniques are discussed for soil slurries, as well as the many limitations of commercially available codes. Geotextile tubes filled with sandy material are used for various tasks around the globe. The rapid consolidation which is observed in these geotextile tubes does not require sophisticated analyses to understand. Consolidation of fine-grained fills, however, is a prolonged process which may impact the projects for which they are used. Numerical models have been created in order to analyze the consolidation of geotextile tubes filled with fine-grained materials in order to better understand their behavior over time. A commercially available finite element code was first used to model the one-dimensional consolidation of a dredged soil from the Gulf of Mexico. The code was shown to produce valid results when compared to the theoretical consolidation behavior of this soil. Then, the geometry of a geotextile tube was modelled. The numerical code was able to produce somewhat accurate results, though it was determined that the results under-predicted the total settlement which the geotextile tube would actually undergo. This observation represents a substantial limitation this numerical code, as well as other similar numerical codes. The code is not capable of modelling near-zero effective stress states, such that a greater-than-zero effective stress must be present in the model at its initialization. For soft soil slurries with very low preconsolidation stresses, this specified initial effective stress may be greater than the preconsolidation stress. To correct the resulting errors in the plasticity model, the soil's preconsolidation stress is artificially increased to the value of the initial effective stress. The consequence is that any volumetric strains which should have occurred at stresses below the initial effective stress are ignored. The process of modelling the full geotextile tube geometry is not yet complete, and additional steps should be taken to better represent the true behavior of a geotextile tube. The model discussed here assumed that the fill material was deposited instantaneously, though this may not always be the case. It is possible that the tube may be filled gradually over time, or that it might need to be refilled after consolidating for an allotted time. Thus, the effects of time-dependent filling of the geotextile tubes should also be analyzed in future modelling efforts. Overall, numerical modelling has produced interesting and useful results, and it has shown that substantial limitations exist in the use of commercially available codes to model slurry consolidation.