Deformation and flow driven by osmotic processes in porous materials

Premi extraordinari doctorat curs 2010-2011, àmbit d’Enginyeria CivilEn el caso del almacenamiento de los residuos radioactivos los flujos osmóticos pueden ser relevantes y requieren un análisis en detalle. El residuo nuclear bituminizado (BW) será almacenado mediante contenedores en cavidades excavadas en la Boom Clay, que es una arcilla marina que presenta propiedades favorables para limitar y retrasar la migración de los contaminantes radioactivos. La interacción entre los dos materiales es un proceso acoplado químico-hidro-mecánico y depende de la respuesta hidromecánica de la Boom Clay y del BW. En condiciones de almacenamiento, el contacto del BW, que contienen cantidades importantes de NaNO3, con el agua subterránea induce la hidratación por gradientes osmóticos y el consiguiente hinchamiento, además de la difusión de la sal disuelta hacia la Boom Clay. Se pueden distinguir dos tipos de afecciones: la perturbación geomecánica causada por el hinchamiento del BW y el aumento de presión en el BW y cambio de las distribución de tensiones en la roca, y la perturbación físico química por la migración de grandes cantidades de sales. El objetivo de esta tesis es: (i) Mejorar la comprensión de los procesos que controlan la absorción de agua y el consecuente hinchamiento del BW que contengan sales (NaNO3), y (ii) Investigar los posibles efectos de la concentración de fluidos de los poros sobre el hinchamiento, la compresibilidad y comportamiento de corte de la Boom Clay. En primer lugar, se ha desarrollado una formulación para el análisis de la deformación inducida por la disolución de sales en medio poroso con contacto con agua. Las ecuaciones planteadas incluyen los flujos acoplados de agua y soluto. Se presenta también un trabajo teórico que ayuda a la comprensión del comportamiento mecánico del BW. Se considera este material como una mezcla de bitumen y cristales de NaNO3. Se ha desarrollado un modelo elasto-viscoplástico que describe el comportamiento de fluencia del BW considerando el comportamiento de fluencia de sus constituyentes. El modelo constitutivo elasto-viscoplástico ha sido implementado en el programa CODE_BRIGHT. Los resultados se han comparado con observaciones experimentales. Se ha estudiado el comportamiento a largo plazo del BW en contacto con agua al simular ensayos de hinchamiento por absorción de agua bajo condiciones confinadas. El análisis numérico ha demostrado ser capaz de proporcionar una representación satisfactoria de los principales patrones observados en su comportamiento. En lo que respecta al segundo objetivo de la tesis, se ha propuesto una formulación para el análisis de las deformaciones inducidas por procesos osmóticos en un medio poroso de doble estructura. Esta formulación distingue dentro del material un nivel micro-estructural y otro macro-estructural con cambios químicos que tienen un efecto significativo en la micro-estructura. Se han obtenido las ecuaciones básicas que describen los flujos acoplados de agua y solutos y el transporte de sus componentes a través de los macroporos así como las ecuaciones de balance de masa para agua y soluto en los macroporos y microporos. La formulación propuesta ha sido aplicada particularmente para analizar cualitativamente el efecto de la succión osmótica sobre el hinchamiento de los suelos arcillosos. Se han analizado los efectos a corto y largo plazo. Se ha investigado también la influencia del aumento de la concentración del fluido en los poros sobre las propiedades geotécnicas y el comportamiento de la Boom Clay no saturada. Se ha llevado a cabo un programa sistemático de investigación experimental, con control de succión osmótica y matricial, con el fin de investigar el efecto del incremento de la concentración del fluido de poros sobre la resistencia de corte y el cambio volumétrico bajo condiciones edométricas. Se ha observado, que bajo condiciones parcialmente saturadas, un cambio en la salinidad provoca una disminución en la compresibilidad y en la resistencia de corte del material.For deep storage of high-level nuclear waste osmotic flows can be significant and so require a careful analysis. In Belgium, The bituminized nuclear waste (BW) named Eurobitum contained in metallic drums will be placed inside a tunnel or a shaft excavated in the Boom Clay, which is 100 m thick marine clay presenting favourable properties to limit and delay the migration of the leached radionuclides over extended periods of time. In Geological disposal conditions, contact of the bituminized radioactive waste which contains high amounts of highly soluble salt (NaNO3) with groundwater will result in water uptake and swelling of the waste and in subsequent diffusion of the dissolved salt through the host clay formation. Basically, two types of disturbance can be distinguished: A geo-mechanical perturbation, caused by the swelling of the waste and the increase of the pressure in and around the waste and a physico-chemical perturbation by the release of large amounts of NaNO3 and other soluble salts. In this context the aim of this thesis is: (i) to improve the understanding of the processes controlling the water uptake and the subsequent swelling of bituminized waste containing soluble salts (NaNO3), and (ii) to investigate of the possible effects of the increase of pore fluid concentration on swelling, compressibility and shear behaviour of Boom Clay. A formulation has been proposed for the analysis of deformation induced by dissolution of salts in porous media in contact with water. The equations include the effect of coupled transport phenomena and the formulation has been included as an extension in the coupled THM program CODE_BRIGHT. A theoretical and experimental work aiming at understanding the mechanical behaviour of the Bituminized Waste has been presented.This material is considered for this purpose as a mixture of bitumen and crystals of NaNO3. An elasto-viscoplastic model has been developed that describes the creep behaviour of BW considering the constituents' creep behaviour. The elasto-viscoplastic constitutive model has been implemented into CODE_BRIGHT. The modelling results have been compared with the experimental data. The impact of osmotic forces on the swelling of the material has been investigated by simulating water uptake swelling tests under confined conditions and comparing the predictions with experimental results. The numerical analysis has proven to be able to furnish a satisfactory representation of the main observed patterns of the behaviour. In regard to the second objective of this thesis, a formulation has been proposed for the analysis of deformations induced by osmotic processes in double structure porous media. The formulation is based on the distinction within the material of a microstructural and a macrostructural levels with chemical changes having a significant effect on the microstructure. A macroscopic description of the system is provided. Then the basic equations describing coupled flows of water and solutes and the transport of its components through macropores and mass balance equations for water and solute in macro and micro pores have been obtained. The proposed formulation has been particularly applied to analyze qualitatively the effect of osmotic suction on swelling of clayey soils. Transient and long term effects have been analyzed. The influence of pore fluid concentration on the geotechnical properties and behavior of Boom Clay under partially saturated conditions has been investigated. A systematic experimental research program involving osmotic suction and matric suction controlled experiments has been carried to investigate the effect of the increase of pore fluid concentration on shear strength and on the volume change behaviour under odometer stress state conditions. It has been observed that under partially saturated conditions a change in salinity causes a decrease in compressibility and shear strength.Award-winningPostprint (published version

Amaryllis belladonna L. (Amaryllidaceae, Amaryllidoideae), first record as naturalized geophyte in Tunisia and continental North Africa

Abstract Amaryllis belladonna L. is recorded for the first time as a naturalized non-native geophyte new to Tunisian and continental North African flora. Additional information on its current distribution and habitat, a brief morphological description, as well as some taxonomic notes, are provided

Echinophora spinosa L. (Apiaceae), a new species in the flora of Tunisia and second report from North Africa

Echinophora spinosa L. (Apiaceae), recently collected from Tabarka (Jendouba-Kroumiria, North-western of Tunisia), is reported as a new species for the terrestrial Flora of Tunisia. It is described and illustrated and notes on its ecology and phytosociological remarks are provided

Further records and new data on the occurrence of Martyniaceae in Tunisia and North Africa

Proboscidea louisianica (Miller) Thell. (Martyniaceae) is newly reported for the flora of Tunisia and North Africa as a naturalised alien. Extensive field investigations in northern Tunisia allowed the discovery of three populations of P. louisianica (Miller) Thell. consisting of 18 individuals were found at the edges of “Oued Beja” and at roadside within an irrigated land in Nabeul region, where plant specimens were in flowers and fruits. Moreover, further sites were recorded for the other member of the family Martyniaceae (Ibicella lutea (Lindl.) Van Eselt.), already reported and known in Tunisia and Algeria within North Africa. Additional information for both species on their current distribution areas and their habits are provided. Details of their morphological and distinguish features are illustrated.Proboscidea louisianica (Miller) Thell. (Martyniaceae) se na novo poroča za rastlinstvo Tunizije in Severne Afrike kot naturaliziranega tujca. Obsežne terenske raziskave v severni Tuniziji so omogočile odkritje treh populacij P. louisianica (Miller) Thell. 18 oseb je bilo najdenih na robovih "Oued Beja" in ob cesti v namakani zemlji v regiji Nabeul, kjer so bili rastlinski vzorci v rožah in plodovih. Poleg tega so bila zaznana nadaljnja mesta za drugega člana družine Martyniaceae (Ibicella lutea (Lindl.) Van Eselt.), O katerem so že poročali in so znani v Tuniziji in Alžiriji znotraj Severne Afrike. Za obe vrsti so na voljo dodatne informacije o njihovih trenutnih območjih razširjenosti in njihovih navadah. Navedene so podrobnosti njihovih morfoloških in ločenih značilnosti

Muscari baeticum (Scilloideae, Asparagaceae), a new addition to the native flora of Tunisia and third report to Mediterranean Africa

Muscari baeticum, originating from western Europe, is here recorded as new from the central eastern part of Tunisia. So far, it was known only from Algeria and Morocco within the southern part of the Mediterranean basin. Description of the species as well as first data about its ecology in Tunisia together with geographical distribution and diagnostic features of closely related species are given. Photographic illustrations of the new reported taxon and an updated key to the Muscari species in North Africa are also provided.Muscari baeticum, ki izvira iz Španije, je tu na novo zabeležen iz središča vzhodno Tunizije, doslej neznanega iz severozahodne obale Sredozemlja. Podan je opis vrste in prvi podatki o njeni ekologiji v Severni Afriki ter diagnostične značilnosti sorodnih vrst. Predstavljeni so geografska razširjenost, ocena IUCN, grožnje in nekateri ukrepi za ohranjanje ex situ. Na voljo so tudi fotografske ilustracije in ključ do vrste Muscari v Tuniziji

Further species within Arecaceae (Palmae; Coryphoideae) to non-native flora of Tunisia and North Africa

New records of allochthonous vascular Tunisian flora are here discovered. Reported taxa (Livistona chinensis, Phoenix canariensis, P. reclinata, P. theophrasti and Washingtonia robusta) belong to the subfamily Coryphoideae (Arecaceae). Updated nomenclature, brief description, general and national distributions are provided for each species. Livistona chinensis and Phoenix theophrasti are here reported for the first time in North Africa. Analytical keys are also provided

Phymosia (Malvaceae) a new genus for the flora of Africa, with nomenclatural notes

Abstract As part of ongoing studies of Tunisian Malvaceae, a population of Phymosia umbellata was discovered in Monastir city. It represents the first generic record for the national and continental flora. Morphological characters, as well as ecological data are given. A list of all the accepted names in Phymosia, their synonyms and types is also provided, with nomenclatural notes about some accepted Phymosia species

Taxonomic and distributive notes on Serapias lingua subsp. Tunetana (Orchidaceae), a rare endemic to Tunisia

Serapias lingua subsp. tunetana, a rare endemic orchid confined to Tunis, northern of Tunisia, has been rediscovered far away from its type locality nearly after 22 years. Since its first finding in 1996 and its description published in 2005, the subspecies has not been found again, and was presumed to be extinct, or the taxon was erroneously identified. A detailed description of the subspecies justifying an amendment to its description, a map of its current distribution and colour photographs are also provided. The affinities to the related taxa within the S. lingua group occurring in Tunisia are here presented. The global IUCN status for this taxon is evaluated

Hertia cheirifolia y H. maroccana (Asteraceae), dos especies endémicas para áfrica del norte: notas nomenclaturales, morfología, distribución y evaluación de la lista roja según la UICN

Hertia cheirifolia and H. maroccana (Asteraceae) are endemic North African species occurring, respectively, in Algeria and Tunisia, and Morocco. Morphological descriptions, distributions, and IUCN Red List assessments are provided in the present paper. In addition, a nomenclatural study of Battandier Hertia maroccana and Linnaean Othonna cheirifolia are carried out and these two names are typified on specimens preserved, respectively, at MPU and LINN.Hertia cheirifolia y H. maroccana (Asteraceae) son dos endemismos norteafricanos que crecen, respectivamente, en Argelia y Túnez, y en Marruecos. Presentamos en este trabajo descripciones morfológicas, distribución y categorización en la lista roja de la UICN. Además, se lleva a cabo un estudio nomenclatural de Hertia maroccana de Battandier and Othonna cheirifolia de Linneo y se tipifican ambos nombres sobre especímenes conservados, respectivamente, en MPU y LINN

On Atriplex canescens (Chenopodiaceae s. str./Amaranthaceae s. l.) in Tunisia: nomenclatural and morphological notes on its infraspecific variability

Populations of Atriplex canescens var. gigantea were found in Lamta, Bouficha-Enfidha (central Tunisia), and Medenine (southern Tunisia). Literature data concerning the presence of this species in Tunisia are contradictory but now our data confirm its occurrence in the country. On the other hand, this variety is reported in the present paper for the first time both in Tunisia and in North Africa in general. Morphological characters and ecological data are presented, as well as notes about patterns of infraspecific variability of A. canescens. Nomenclatural notes on infraspecific names in A. canescens, as well as on the closely related species A. garrettii, are provided. The types of the names A. canescens var. laciniata, A. canescens var. macilenta, A. garrettii, Obione occidentalis var. angustifolia, and Pterochiton occidentale, that in earlier publications were erroneously considered to be holotypes, are in fact lectotypes (for most of taxa) or a neotype (for Pterochiton occidentale) under Art. 9.10 of the ICN. Isolectotypes were found at CAS (A. canescens var. laciniata and A. canescens var. macilenta), GH (A. canescens var. macilenta), and YU (Atriplex nuttallii)