Tesis doctoral de Abel Carlos Jacinto
This thesis presents the results of the research carried out in the framework of the temperature buffer test (tbt) project. The overall objective of this project is to investigate how well the bentonite used in engineered barriers can endure the high temperatures expected to be found around vitrified waste canisters. Within the project, a full-scale field test that simulates the deposition of high level radioactive waste has been implemented. Additionally, laboratory experiments were carried out to evaluate the response of the bentonite used in the project under different external actions. coupled formulations used to analyse the behaviour of an engineered clay barrier are written in terms of the state variables by using constitutive relations. Among these laws the soil water retention curve (swrc) defines the constitutive relationship between the amount of water in the soil and its energy status. Traditionally, the influence of external variables like temperature and soil fabric on the water retention capacity of soils has been analysed using concepts derived from the capillary model. However, theses analyses systematically failed to explain the experimental observations. In this thesis, experimental data obtained on bentonite samples tested at different temperatures and densities were evaluated using an approach derived from concepts of thermodynamic of adsorption. This approach also gives a tool to introduce in a simple way the effect of temperature and sample porosity in numerical simulations. it is generally accepted that the interaction between smectite, which is the main mineral of bentonite, and water changes the properties of the water retained in the soil. In particular, values of the water density higher than 1.0 mg/m3 (i.E. The density of the free water) have been suggested by experiments at mineralogical level as well as by data obtained on compacted samples of expansive clays. From a practical point of view this effect traduces in values of degree of saturation higher than one at lower values of suction. This is important when a numerical analysis is being performed, as balance equations are based on the degree of saturation as the main variable to indicate the water content within the porous medium. In this thesis a methodology that defines the water density as a function of the energy of the water within the soil pores was developed. This method was applied to analyse published data about the water retention capacity for compacted samples of different bentonites. the analysis of the mechanical response of expansive clays under external actions as those typically found in engineered barriers is a complex task. Constitutive models used in numerical calculations have to be able to simulate the main aspects of the material response. Models previously developed to simulate the behaviour of compacted samples made up of expansive clay were adopted in this thesis. Parameters in these models were calibrated using experimental data corresponding to compacted samples of mx-80 bentonite, the material adopted as reference in the tbt project. concepts developed in the thesis were included in a numerical code able to solve coupled problems in deformable porous media. This code was then applied to the analysis of a mock-up experiment and to the simulation of the in situ test carried out within the framework of the tbt project. Theses numerical simulations showed the capabilities of the code to capture the general tendency of the experimental data. Additionally, the analysis of numerical results enhanced the understanding of the different phenomena that take place in coupled processes as well as the interaction mechanisms between them.
Datos académicos de la tesis doctoral «Thermo-hydro-mechanical behaviour of expansive clays under high temperatures«
- Título de la tesis: Thermo-hydro-mechanical behaviour of expansive clays under high temperatures
- Autor: Abel Carlos Jacinto
- Universidad: Politécnica de catalunya
- Fecha de lectura de la tesis: 09/09/2010
Dirección y tribunal
- Director de la tesis
- Alberto Ledesma Villalba
- Tribunal
- Presidente del tribunal: eduardo alonso Pérez de ágreda
- marcelo Sanchez castilla (vocal)
- pierre Delage (vocal)
- María victoria Villar galicia (vocal)
