Numerical modelling of unsaturated soils with the material point method
(English) The Material Point Method (MPM) is presented as an advanced numerical method used to simulate geotechnical problems subjected to large deformations and soil-structure interaction problems, such as landslides, penetration issues, and collapse of geotechnical structures. Its main advantage i...
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| Formato: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2024 |
| País: | España |
| Recursos: | CBUC, CESCA |
| Repositorio: | TDR. Tesis Doctorales en Red |
| OAI Identifier: | oai:www.tdx.cat:10803/695196 |
| Acesso em linha: | http://hdl.handle.net/10803/695196 https://dx.doi.org/10.5821/dissertation-2117-441596 |
| Access Level: | acceso embargado |
| Palavra-chave: | Àrees temàtiques de la UPC::Enginyeria civil 624 - Enginyeria civil i de la construcció en general |
| Resumo: | (English) The Material Point Method (MPM) is presented as an advanced numerical method used to simulate geotechnical problems subjected to large deformations and soil-structure interaction problems, such as landslides, penetration issues, and collapse of geotechnical structures. Its main advantage is the ability to simulate large movements without the mesh-related problems typical of the standard Finite Element Method (FEM). Simulating different material states and external conditions is a challenging aspect in geotechnical engineering. This process requires a detailed analysis of how to address phenomena such as rainfall and water flow through the soil. Additionally, it is crucial to incorporate material constitutive relationships to properly replicate or predict stress-strain behavior. The modelling of unsaturated soils is necessary in various fields, especially in geotechnical works employing compacted materials such as embankments, dams, fills, and natural slopes. The study and analysis of these soils requires modelling the entire process of the work, from its construction, if applicable, to post-failure behavior. Until now, simulating the unsaturated state of materials has mainly relied on FEM, assuming small deformations at a theoretical level. This involves developing coupled mechanical and hydraulic constitutive models and utilizing advanced numerical tools. This Thesis presents advancements in modelling unsaturated soils in large deformation problems through the development of the MPM. The formulation of a single-point, multi-phases has been used, showing its potential for improving the accuracy and reliability of geotechnical simulations involving large deformations. Firstly, the developments for simulating boundary conditions for unsaturated soils (imposed flow and seepage condition) are presented. These conditions are complex, particularly since the boundary where they are applied is not fixed and must be determined during the calculations. Validation of these conditions is consistently performed using a soil column subjected to infiltration flow. The results are compared with those obtained from a widely used finite element code, giving similar results. Next, for the first time, the modelling of wetting collapse in MPM is proposed. A constitutive model is implemented to capture the key characteristics of unsaturated material behavior. This model is based on critical state theory and employs two alternative formulations, depending on whether Bishop's stress or net stress is used, along with suction. Validation is conducted through conventional laboratory tests. The loss of volume due to wetting is analysed, a characteristic associated with unsaturated soils with an open structure. The loss of suction in the material leads to a loss of strength and, consequently, the possibility of failure. This is illustrated by a physical test conducted in a centrifuge on a slope subjected to a rising water table from the base, which results in the evolution of the saturation front, collapse-induced deformations, and ultimately a landslide when critical saturation conditions are reached. Finally, one of the objectives of this Thesis is to model the entire process of a geotechnical project. To achieve this, a numerical scheme was implemented to simulate construction stages, representing a significant advancement in the application of the MPM for analysing material behavior during the pre-failure stage. Modelling of the construction process is crucial because it not only represents the construction process and the displacements occurring during it, but also establishes the initial state of the structure for subsequent analysis stages. The proposed scheme effectively captures deformations and failure processes during construction, unlike conventional methods based on Eulerian formulations, which cannot accommodate large material displacements during construction |
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