Estudio del comportamiento de colapso en arenas arcillosas bajo un estado generalizado de tensiones
- Autores: Octavio Enrique Cardenas Diaz
- Directores de la Tesis: Enrique Edgar Romero Morales (dir. tes.), Antonio Lloret Morancho (dir. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2018
- Idioma: español
- Tribunal Calificador de la Tesis: Alberto Ledesma Villalba (presid.), Diana Marcela Gómez-Sánchez (secret.), Cristina Jommi (voc.)
- Programa de doctorado: Programa de Doctorado en Ingeniería del Terreno por la Universidad Politécnica de Catalunya
- Materias:
- Texto completo no disponible (Saber más ...)
- Resumen
This thesis studies the hydro-mechanical behaviour of a compacted clayey sand under generalised stress state. The study, which is mainly experimental, focuses on the analysis of the shear strength at different hydraulic states and on the collapse response during flooding. These behavioural features have important applications in the design of earthworks (dams and embankments), which are structures that undergo significant water content changes along their different construction stages. However, despite this important practical issue, there are few experimental studies that have evaluated these behavioural features, particularly during flooding under generalised stress state, and that includes the control of the deviatoric stress, the mean net stress and the Lode angle during the development of the collapse.
Within the experimental study, a hollow cylinder apparatus was set up with automatic control of the internal and external chamber pressures, as well as of the axial stress. The apparatus was designed for saturated soils, and an important calibration was carried out to determine the global radial and circumferential strains using the information of the volume changes of the internal and external cell chambers.
The material used in the research was a mixture of 30% (by mass) of sand from Castelldefels (Barcelona) and 70% silty clay from Campus Nord (Barcelona). The selection of the most suitable mixture and of the initial compaction conditions –to ensure an adequate shear strength, saturated permeability and to display an important collapse during flooding– was done after an extensive geotechnical characterisation program of the constituent materials and various proportions of the mixtures.
Microestructural and hydraulic characterisation tests (mercury intrusion porosimetry, water retention curve and permeability), as well as mechanical tests at different states and hydraulic paths (shear strength in triaxial and direct shear cells, compressibility and soaking tests under oedometer conditions) were performed on the selected mixture. These preliminary tests allowed calibrating the different parameters of the elasto-plastic BBM model, as well as to define the position of the yield surfaces.
Tests on the hollow cylinder apparatus were performed on saturated and partially saturated samples along isotropic compression and shear paths (increase in deviatoric stress at constant mean stress). These last paths were performed at four different Lode angles. Shear strength results at ultimate conditions allowed defining the variation of the cohesion with suction, as well as the dependence of the slope of the critical state line on the Lode angle (considered independent of suction). Finally, collapse tests (saturation) were carried out at the same mean stress and deviatoric stress state but at different Lode angles and therefore at different distances from the critical state line. The saturation of the sample was carried out by flooding with water from the base of the cell without suction control. The experimental results, which will be useful for future research, showed larger collapse when the intermediate stress coincided with the minor stress, as in the case of an axi-symmetric triaxial compression test.
The time evolutions of the collapse deformations were simulated using a 1D infiltration model with constant permeability and the BBM model (considering the dependence of the slope of the critical state line on Lode angle). The simulations showed a collapse that was not largely affected by the Lode angle, although the evolutions of the directions of the plastic flow vectors changed significantly between the different conditions of the tests, as detected in the different experimental results.
