SOIL MECHANICS IN CONSTRUCTION

Author: DELAHAYE MIRACHI CARLOS HECTOR.
Year: 2004.
University: POLITÉCNICA DE CATALUÑA [www.upc.edu].
Place of defense: AULA SEMINARIO-EDIFICIO D2- 2ÂMa. PLANTA.
Place of preparation: EDIFICI D2 Campus NORD.

Summary: The thesis entitled "Modeling of the migration of gas through a porous medium low permeability", is closely related to the study of the behavior of compacted soil at high densities, which are used in the construction of barriers engineering repositories located radioactive waste in deep geological formations. These are composed of compacted soil clay (usually bentonite), mixtures of clay and sand, material cemented based on Portland cement, and crushed rock salt. The study of the effects of gas generation and migration in the repository, on barriers engineering and interaction with the solid rock that surrounds it, has provided the general framework of the work of the thesis. This frame work comprises two main issues highly related: a) gas generation and b) gas transportation. The thesis has been approached to vet the second major issue, but taking into account the first in the development of work. The migration of gas through the backfill of the barrier is a very complex problem, since phenomena thermal, hydraulic and mechanical are strongly coupled. This has required the development of the thesis is carried out within a framework of appropriate research. The work involved the following studies: A) Revision of the existing information on the generation and transportation of gas repositories. This study (Chapter 2) has allowed fundamentally understand and identify mechanisms gas transmission and evaluating existing models in the literature. B) Adopt a framework teórico-experimental appropriate. At this stage (Chapter 3) is adopted as part of the work flow systems multifase-multiespecie, applied to the mechanics of unsaturated soils. It also defines the general features that should play a numerical code to reproduce in a natural way, most of the phenomena associated THM transport gas in a deep geological disposal of nuclear waste. C) Modeling THM transport gas in the conceptual design of a Spanish PGA granite. In this study (chapter 4) is an initial estimate of the behavior of gases generated in the repository, using the most current information on the geometry of the design, materials considered and boundary conditions. The main benefit of this work was to evaluate the predictive ability of a numerical model coupled THM and provide a basis for future models. D) A study of the migration of gas in clay. Modeling hydromechanics of gas migration experiments in the laboratory, the effect of heterogeneity and gas flow through preferential pathways (Chapters 5, 6 and 7). At this stage deals with the study of gas migration through clays, which are viewed as a possible material for the construction of the barrier as engineering to hosting the repository. Significant progress has been made in understanding the complex phenomenon of migration of gas through clay formations, in particular, the problem of gas flow through preferential pathways. E) Modeling hydromechanics the migration of gas in the test model (Mock-up) and the trial âin situâ Project GMT (Chapters 8 and 9). In this work we have achieved concrete progress in the study of gas migration through the barrier of engineering and evaluation of conceptual models and numerical. This has enabled to provide data to improve the design of the 8 barrier 351 engineering and test its procedures for construction and placement on mock trial, and in the silo for the storage of waste intermediate under real conditions on the spot.

Author: HOFFMANN JAUGE CHRISTIAN.
Year: 2004.
University: POLITÉCNICA DE CATALUÑA [www.upc.edu].
Place of defense: Aula 212 - Edificio D2.
Place of preparation: EDIFICI D2 Campus NORD.

Summary: Currently, the use of atomic energy accounts for 16% of the total energy that is produced globally. One of the biggest problems facing their use, go find a secure solution for storing the waste resulting from the process of energy production. One of the most studied and accepted as a solution to this problem, is the construction of underground reservoirs where maintain the residue isolated during the remainder their lives, ENRESA (2000), Reseal (2000). PRACLAY (1998). These tanks are designed in accordance with the criterion multibarreras: set of independent and redundant barriers that keep the waste isolated. Waste disposal is inside metal containers, in horizontal or vertical niches, dug in the rock. To fill the space between the rock and metal container was looking for a material that represents a real barrier insulation, called, barrier engineering. These materials consist mostly by bentonite. Project EB, the study proposes a new concept of underground storage of radioactive waste for long activity. The residue is available in metal containers housed in horizontal niches in a rock excavated clay (Opalinus clay), and as insulating material, it uses a combination of blocks and compacted bentonite pellets. Both materials are manufactured from a single bentonite, the bentonite Febex, ENRESA (2000). This doctoral thesis, is associated with the experimental characterization of the behavior of the hydro pellet samples, conducted under the project EB. To study the most significant aspects of the response of the material is necessary to combine different experimental techniques for the control of suction (Romero, 2001) and bring the different testing methodologies. Work on the thesis were conducted in three basic stages: a first stage in which he studied the structural characteristics of the mixtures of bentonite pellets. Samples were prepared with different densities dry and conducted tests porosimetrías mercury (IPM) and infiltration tests. Once this first stage, defined a working methodology and were carried forward the various trials pilot program. At this stage describes the various experimental techniques and equipment as well as the results obtained in the various trials divided into three groups; tests characterization hydraulic behavior, secondly testing expansion, swelling and compressibility with the suction control and finally tests carried out to study the influence of the type of water transfer rate of wet and the behavior of the material. In the last stage, raised the conceptual foundations and laws constitute a model suitable for expansive (Model BExM, Gens & Alonso (1992) and Alonso et al. (1999)). The model was implemented in a numerical code using the technique of finite differences and applied to the case of mixtures pellet Bentonite. It details the implementation of the various equations and describes the iterative used to raise its resolution. Additionally, we suggest a methodology for the deduction of the various parameters of the model indicates the capabilities of the model in different models and comparing the model predictions with the actual behavior observed. At the end of the thesis, presents the experimental results obtained in a test at medium-scale, so-called tests Column Infiltration. The objective of these tests is to study the response of the material or 8 na escal 300 average, in very controlled and similar to those in use as materials, a barrier engineering.

Author: LÓPEZ QUEROL SUSANA.
Year: 2005.
University: CASTILLA-LA MANCHA [www.uclm.es].
Place of defense: ESCUELA SUPERIOR DE INGENIEROS DE CAMINOS, CANALES Y PUERTOS DE CIUDAD REAL.
Place of preparation: ESCUELA TÉCNICA SUPERIOR DE INGENIEROS DE CAMINOS CANALES Y PUERTOS.

Summary: The properties of the soils have changed consideration when they are subjected to dynamic type of solicitations. The constitutive models that reproduce the correct behavior of soils in static situations become unable to predict how evolving tensions and strains when the applied loads are time varying. However, the dynamic load with a lot more frequent than the static in nature. The most dramatic situations experienced in the earthquakes, where soils are severely deformed greatly altering its character, and where the structural exhaustion suffered by the geoestructuras, the decline in bearing capacity in the foundations, and avalanches produced mountainsides produce in each of these unfortunate episodes the loss of many human lives and property. The constitutive models whose purpose is to analyze these kinds of problems are not simple at all. Its complexity is increased further by the presence of water in contact with the solid particles. In that case, the models must represent the behavior of each phase coexisting in the soil, as well as the interaction between them. In eta doctoral thesis has done a numerical model to represent the dynamic behavior of granular soils not cohesive. The interactions of chemical and thermodynamic are not considered in this new tool, which is found only type mechanical relationships between the different components of soil. This new model is able to reproduce extreme conditions of the soil saturation; completely dry or completely saturated. There are many models for the same purpose that developed here. Most of them, however, are based on theories plastic, and require calibration of a large number of parameters, and most delos who lack physical meaning. This thesis has sought a model that represents the physical process of liquefaction and / or cyclic mobility. These phenomena occur in saturated granular soils as a result of redeployment of solid skeleton subjected to vibration and has resulted in the drastic reduction of the actual pressure of the soil. To address this modernization is part of the analysis of the densification of dry sand, and then raised the interactions between phases when the soil is saturated, and correlate the changes in pressure of interstitial voids with the decline in volume caused by reordering grains solid. This model, based on the densification, is not new. However, this theory has been pursued further rationalization in the calculation, the correlation with the parameters of the law of densification (based on the well-known model endocrónico) with some mechanical properties of the sand. There is thus a generalization of densification of the law, according to which only is required calibration of a single parameter for each type of sand has been also developed a new method to determine the solicitation harmonic equivalent deformations. This new method is consistent with the model endocrónico, and has the advantage of not needing the estimate of the extent of solicitation equivalent, which is obtained as a result of the calculation. On the other hand, no model of this kind is alright if trajectories tensions are not properly modeled. This has been considered separately behavior contractivo and dilatativo soil, depending on the status of the line tr 8 ansforma d03-phase at the level of tension, which in turn correlates with the initial state of compactness. It has developed a new rule flow not associated with a value of dilatancia that depends on a new state parameter that quantifies the state of soil degradation since the beginning of the solicitations. Moreover, the situations of the collapse of the soil are also considered by the same model constituent. The law creating here represents developed in an integrated manner all these behaviors tenso-deformacionales. The end result is a constitutive law that requires calibration of a total of seven parameters. This calibration has been addressed for different soil types on the basis of results of court cyclic voltage controlled and constant volume. Once certain plastic deformation experienced volumetric soil to be subjected to vibration, adding acomplamiento type viscous phases between solid and fluid, and apply the laws of evolution of modulus of elasticity module and volumetric strain, trying to reproduce the mechanical behavior of the soil. Then there has been implementing the law developed a numerical model in two-dimensional finite elements. Before proceeding to make comparisons between actual results and model, has ensured the smooth operation numeric comparison with problems with simple analytical solution, and the program GeHoMadrid, which has been widely contrasted by their authors. Subsequently, have modeled some tests of the Universtity of centrifugal British Columbia and the project VELACS, and then compared the results of numerical pressure, acceleration and displacement with the pilot. This has quantified the degree of confidence that the new model to draw conclusions about the behavior of granular soils. Then there has been a simplified model of a break in the Lower San Fernando Dam, as a result of which is obtained very accurately the location of the break and began the instant it occurred. To end the argument, it applies the numerical model developed some practical problems in obtaining findings behavior. These problems are of various kinds, and represent both situations in open fields and in the laboratory. In implementing the behavior of geoestructuras identifies certain types of failure by liquefaction, as well as some solutions that best palliative presented as recommendations design earthquake zone.