Literatura académica sobre el tema "Transitional soils"

Tese (doutorado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Civil e Ambiental, 2016.<br>Submitted by Fernanda Percia França (fernandafranca@bce.unb.br) on 2016-05-02T13:16:42Z No. of bitstreams: 1 2016_BrunadeCarvalhoFariaLimaLopes.pdf: 10524732 bytes, checksum: 6a3926fa46c3ae98ed72a5747107ed80 (MD5)<br>Approved for entry into archive by Marília Freitas(marilia@bce.unb.br) on 2016-05-26T17:07:34Z (GMT) No. of bitstreams: 1 2016_BrunadeCarvalhoFariaLimaLopes.pdf: 10524732 bytes, checksum: 6a3926fa46c3ae98ed72a5747107ed80 (MD5)<br>Made available in DSpace on 2016-05-26T17:07:34Z (GMT). No. of bitstreams: 1 2016_BrunadeCarvalhoFariaLimaLopes.pdf: 10524732 bytes, checksum: 6a3926fa46c3ae98ed72a5747107ed80 (MD5)<br>O futuro da prática da engenharia é a incorporação de aspectos da microestrutura nas características macroestruturais dos solos de modo a simplificar e tornar mais realistas as análises geotécnicas. Consequentemente, é de fundamental importância que se entenda a estrutura dos solos em diferentes estados (inderformado, reconstitutído, remouldado, compactado, etc.) e se correlacionem os mesmos, já que se sabe que o estado inicial do solo dita o seu comportamento. Neste sentido, esta pesquisa está focada no desenvolvimento do entendimento das mudanças na estrutura do solo através dos tamanhos dos seus poros e sua distribuição quando submetido a carregamentos mecânicos assim como a determinação do estado mais apropriado para descrever um estado de referência do comportamento do solo. Os solos testados foram duas argilas: Caulinita e Ball; e um solo tropical transicional: Solo de Brasília. A partir dos solos estudados foram produzidas amostras com pH 9, reconstituídas, remoldadas e indeformadas, esta última somente para o solo de Brasília. Cada uma destas amostras foi submetida à compressão unidimensional combinada no oedometro e aparelho de taxa constante de deformação a diferentes tensões: 2, 90, 360, 2.000, 5.000 e 11.000kPa. Em seguida as amostras foram congeladas e secas pelo processo de liofilização e por último foram submetidas ao ensaio de porosimetria por intrusão de mercúrio. Adicionalmente, mediu-se a sucção inicial de algumas das amostras dos três solos estudados. A partir dos resultados dos ensaios realizados foram propostos dois modelos conceituais um para as argilas e outro para o solo transicional. Os resultados do ensaio de adensamento foram modelados usando uma adaptação do modelo constitutivo SCLAY-1S (Koskinen et al., 2002) na qual a variável x descreve os efeitos da estrutura ao invés de cimentação como proposto originalmente. Além disto, a amostra pH 9 foi considerada a amostra de referência, assim para este estado x = 0 e todas as outras amostras tem estrutura, de acordo com a metodologia aqui proposta. Os resultados mostraram que a metodologia proposta para obtenção das amostras é adequada. A sucção inicial foi satisfatoriamente correlacionada à tensão de preadensamento. Resultados das análises de porosimetria confirmam que o estado da estrutura das amostras com pH 9 é mais adequado para representar um estado de referência que o estado das amostras reconstituídas. As amostras com pH 9 apresentam uma estrutura dispersa já que as laterais da partícula de caulinita são carregadas negativamente assim como as faces. Dessa forma com o aumento do carregamento não há muitas configurações possíveis, a estrutura da amostra irá ficar cada vez mais orientada e alinhada paralelamente. O mesmo acontece com as amostras em outros estados. A amostra indeformada apresenta inicialmente a estrutura mais aberta, seguida da reconstituída e remouldada. À medida que o carregamento aumenta a estrutura destas outras amostras tende para uma configuração dispersa com as partículas de caulinita orientadas e alinhadas paralelamente. A modelagem constitutiva se mostrou apropriada, embora ainda haja necessidade de aprimoramento nos estudos para que o parâmetro ax possa ser correlacionado com a variável x. _________________________________________________________________________________________________ ABSTRACT<br>The future of engineering practice is to incorporate aspects of the microstructure into the macroscopic characteristics of soils in order to simplify and make the geotechnical analysis more realistic. Therefore, it is fundamentally important to understand the structure of soils in various states (undisturbed, reconstituted, remoulded, compacted, etc.) and correlate them, as it is already known that the initial state of the soil dictates its behaviour. Hence, this research focuses on developing an understanding of the changes in the soil structure through its pore sizes and distribution under mechanical loading, as well as determining which state is appropriate to describe a reference state of the soil behaviour. The soils tested were the two clays: Kaolin and Ball; and the tropical transitional soil: Brasilia Soil. From the studied soils, samples with pH9, reconstituted, remoulded and undisturbed (for the Brasilia Soil only), were produced. Each of these samples was subjected to uniaxial compression combined with oedometer and Constant Rate of Strain (CRS) apparatus up to: 2, 90, 360, 2,000, 5,000 and 11,000 kPa. Specimens of these samples were then freeze-dried by the lyophilization process and lastly subjected to the Mercury Intrusion Porosimetry (MIP) test. Additionally, the initial suction of a few samples of the three soils was measured. From the results of the laboratory tests carried out, two conceptual models were proposed: one for the clays and one for the transitional soil. The results of the consolidation test were modelled using an adaptation of the constitutive model, SCLAY-1S (Koskinen et al., 2002), in which the variable x describes the structure rather than bonding as originally proposed. Furthermore, the pH9 sample was considered the reference state; thus this state has x = 0, while all other states have some structure, according to the methodology herein proposed. Results showed that the methodology proposed for obtaining the specimens is adequate. The initial suction measured was satisfactorily correlated to the preconsolidation stress. Results of the MIP confirmed that the pH9 state is the most suitable to represent a reference state, rather than the reconstituted state. The pH9 state presents a disperse structure, as the edges of the kaolinite particle are charged negatively as well as the faces. Therefore, as the loading increases there are not many possible configurations for this sample, hence the structure will orient in a preferential direction. The same happens for the samples in other states. The undisturbed sample has the most open structure, followed by the reconstituted and remoulded states. As the loading progresses, the structure of these samples tends towards the dispersed configuration with the kaolinite particles well-oriented and aligned in parallel with each other. The constitutive modelling is appropriate; however, there is still room for improvement studies to correlate the parameter ax with the state variable x.

[EN] The understanding of the mechanical behaviour of natural intact soils is central to engineers when designing new structures. The research carried in this thesis focused on investigating the effects of the naturally occurring in-situ structure on the mechanical behaviour of two shallow recently deposited Holocene alluvial materials, the Bormida River silts (BRS) from Italy and the Valencia silty soils (VSS) from the alluvial plains of the Turia River, Spain. These types of deposits are frequently characterised by highly heterogeneous in-situ structures. A large range of soils with different size distributions from sands to silty clays were investigated. Oedometer and triaxial tests were carried out on intact, slurry and compacted samples. The first step was to characterise the behaviour of the materials at their reconstituted state to define the reference framework for investigating the effect of the in-situ structure of the intact specimens. The effects of the sample preparation technique on the mechanical behaviour were examined, in particular its influence on the uniqueness of the normal compression line and critical state line. The initial structure created during the preparation of the specimens was totally removed after compression and shearing regardless of the sample preparation method. Only one soil displayed a clear effect of the sample preparation technique, the oedometer compression lines of which remained parallel to each other even at a very high stress levels for the case of the slurry samples. This result showed that contrary to what is stated in the literature the sample preparation technique can created very robust initial structures resulting in a transitional behaviour. Clears effects of the in-situ structure of the intact samples of the BRS and VSS were observed on the oedometer compression behaviour even at very high stress levels with stress sensitivity values still larger than unity at the end of the tests. It appeared that the effects were more noticeable as the degree of heterogeneity inside the specimens increased at a meso-structure level as it was the case of some samples of the VSS materials which exhibited a certain layering. Small effects of the in-situ structure were seen at large shearing strains and only on the wet side of the critical state.<br>[ES] El conocimiento del comportamiento mecánico de los suelos en su estado natural es de importancia capital para los ingenieros a la hora de diseñar nuevas obras. La investigación desarrollada en esta Tesis se centra en descubrir los efectos que tiene la estructura del suelo en su estado natural en la respuesta mecánica de dos suelos aluviales holocenos, depositados superficialmente: los limos del río Bormida (BRS) en Italia y los suelos limosos provenientes de la llanura aluvial del río Turia (VSS) en España. Este tipo de suelos se caracterizan frecuentemente por una estructura inicial altamente heterogénea. Se ha ensayado una gran variedad de muestras con diferentes granulometrías, desde arenas a arcillas limosas en las que se han realizado ensayos edométricos y triaxiales en muestras intactas, compactadas y en muestras reconstituidas (slurry). En una primera etapa de la investigación se caracterizó la respuesta del material en su estado reconstituido para definir un marco de referencia con el que poder comparar la respuesta de las muestras intactas tomadas in situ y que preservan su estructura natural (inalteradas). Se ha analizado la influencia del modo de preparación de las muestras en su comportamiento mecánico, y, en particular, en la unicidad de las curvas de compresión noval y de estado critico. Se ha comprobado que la estructura inicial inducida durante el proceso de preparación desaparece completamente tras someter la muestra a compresión y corte, independientemente del método de preparación utilizado. Únicamente un suelo mostró, de un modo nítido, el efecto de la técnica de preparación, de modo que las líneas de compresión edométrica se mantuvieron paralelas incluso a niveles de tensión elevados en el caso de muestras reconstituidas (slurry). Este resultado demostró, contrariamente a la opinión aceptada en la bibliografía, que el sistema de preparación de la muestra puede crear una potente estructura inicial dando lugar a un comportamiento de tipo transicional. En los ensayos de compresión edométrica se ha podido comprobar un claro efecto positivo de la estructura inicial de las muestras intactas, incluso a niveles altos de tensión, observándose índices de sensitividad tensional superiores a uno al final de los ensayos, de modo que para igualdad de índice de huecos, la tensión efectiva vertical de la muestra intacta es superior a la correspondiente en la muestra reconstituida. Aparentemente, este efecto es tanto más significativo cuanto mayor es el grado de heterogeneidad interno de la muestra a nivel de meso-estructura, como se pudo observar en algunas muestras de los suelos (VSS) que presentaban niveles de laminación horizontal. En los ensayos de corte la influencia de la estructura intacta fue relativamente pequeña y únicamente en el lado húmedo del estado critico.<br>[CAT] Conèixer el comportament mecànic dels sòls en el seu estat natural és d'importància capital per als enginyers a l'hora de dissenyar noves obres. La investigació desenvolupada en aquesta Tesi se centra a descobrir els efectes de l'estructura del sòl en el seu estat natural en la resposta mecànica de dos sòls al¿luvials holocens, dipositats superficialment: els llims del riu Bormida (BRS) a Itàlia i els sòls llimosos provinents de la plana al¿luvial del riu Túria (VSS) a Espanya. Aquests tipus de sòls es caracteritzen sovint per una estructura inicial altament heterogènia. S'ha assajat una gran varietat de mostres amb diferents granulometries, des d'arenes fins a argiles llimoses amb les quals s'han realitzat assajos edomètrics i triaxials en mostres intactes, compactades i en mostres reconstituïdes (slurry). En una primera etapa de la investigació es va caracteritzar la resposta del material en el seu estat reconstituït per a definir un marc de referència amb el qual poder comparar la resposta de les mostres intactes preses in situ i que preserven la seua estructura natural (inalterades). S'ha analitzat la influència del mètode de preparació de les mostres en el seu comportament mecànic i en particular, en la unicitat de les corbes de compressió noval i d'estat crític. S'ha comprovat que l'estructura inicial induïda al llarg del procés de preparació desapareix completament després de sotmetre la mostra a compressió i tall, independentment del mètode de preparació utilitzat. Únicament un sòl va mostrar clarament l'efecte de la tècnica de preparació, de manera que les línies de compressió edomètrica es van mantenir paral¿leles fins i tot a nivells de tensió elevats en el cas de mostres reconstituïdes (slurry). Aquest resultat va demostrar, contràriament a l'opinió acceptada en la bibliografia, que el sistema de preparació de la mostra pot crear una potent estructura inicial donant lloc a un comportament de tipus transicional. Als assajos de compressió edomètrica s'ha pogut comprovar un clar efecte positiu de l'estructura inicial de les mostres intactes, inclús a nivells alts de tensió, observant-se índexs de sensitivitat tensional superiors a la unitat al final dels assajos, de manera que per a igualtat d'índex de buits, la tensió efectiva vertical de la mostra intacta és superior a la corresponent en la mostra reconstituïda. Aparentment, aquest efecte és més significatiu quant major és el grau d'heterogeneïtat intern de la mostra a nivell de meso-estructura, com es va poder observar en algunes mostres dels sòls (VSS) que presentaven nivells de laminació horitzontal. Als assajos de tall la influència de l'estructura intacta va ser relativament petita i únicament en el costat humit de l'estat crític."<br>Carrión Carmona, MÁ. (2016). The effects of the structure on the mechanical behaviour of young Holocene alluvial materials from the Bormida River (Italy) and Turia River (Spain) [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/63470<br>TESIS

La transition agroécologique vise la triple performance agronomique, écologique et sociétale des exploitations agricoles. Un certain nombre de pratiques agricoles permet d’envisager la construction et le développement de systèmes de culture répondant à ces contraintes. Les légumineuses, par leur capacité à fixer l’azote atmosphérique, sont une alternative intéressante aux intrants azotés. Outre l’absence de fertilisation lors de leur culture, elles fournissent de l’azote à la culture suivante. Il existe cependant un manque de références sur certaines légumineuses à graines et notamment la culture du pois d’hiver. En effet, si des données acquises dans différentes régions françaises sont disponibles, aucune référence n’a été publiée pour la Normandie où la culture du pois d’hiver connaît un récent regain d’intérêt. Cette thèse propose d’évaluer, sur une période de deux ans, l’effet du remplacement du colza par le pois d’hiver en tête de rotation en réalisant une analyse comparative de ces deux successions (pois d’hiver-blé et colza-blé). L’objectif était d’évaluer l’effet de ce changement de tête de rotation (pois d’hiver vs colza) sur l’état biologique du sol et les flux d’azote à différentes échelles spatiotemporelles. Les résultats ont révélé une forte variabilité spatio-temporelle dans la réponse des communautés microbiennes du sol, et mis en évidence l’importance du contexte pédoclimatique dans le déterminisme de l’abondance et de l’activité des communautés microbiennes du sol. Ils ont montré par ailleurs, l’effet positif du pois d’hiver sur la disponibilité de l’azote minéral au cours du cycle cultural et pour les cultures suivantes, ici le blé puis l’orge. Les apports d’azote minéral dans le sol lié à la contribution des parties racinaires via la rhizodéposition et à la dégradation des résidus de culture après récolte ont été évalués au cours de ce travail de thèse. En effet, si la rhizodéposition s’est révélée plus importante sous pois d’hiver, elle n’a pas eu d’impact significatif sur les communautés microbiennes rhizosphériques. Contrairement à ces observations, la dégradation des résidus de culture a significativement modifié la composition des communautés bactériennes en lien avec leur composition biochimique initiale. La succession culturale incluant le pois a enrichi le sol en azote minéral mais des risques de perte d’azote par lixiviation de l’ordre de 23 kg N. ha-1 ont été estimés. Ces constats soulignent l’importance d’adapter la conduite des systèmes de culture incluant le pois d’hiver, en limitant les pertes d’azote par lixiviation et en maximisant son utilisation par les cultures suivantes. Les résultats de ces travaux ont confirmé la diminution des quantités d’engrais azoté utilisées dans la succession contenant le pois, sans préjudice de productivité, ni pour le pois, ni pour la culture suivante, ici, le blé. Finalement, introduire le pois d’hiver dans la rotation de culture en région Normandie, semble permettre de répondre à la problématique d’augmentation du coût des intrants, et aux enjeux de transition agroécologique et d’autonomie protéique régionale<br>The agroecological transition targets triple agronomic, ecological, and societal performance of farms. Some new agricultural practices had emerged to develop a new cropping system to respond to these constraints. Legumes constitute an interesting alternative. Indeed, legumes are advantageous for soils due to their symbiotic relationship with nitrogen-fixing bacteria. The presence of compatible rhizobia combined to nitrogen-limited conditions promotes symbiosis which is the most efficient way for legumes to acquire more nitrogen. Compared with non-nodulated plants, symbiosis provides a competitive advantage by increasing soil nitrogen pool. However, some grain legumes, notably winter pea, are rarely studied, especially in the Normandy region where no reference has been published for this crop. The objective of this study is to compare two crop successions for a period of two years (winter pea-wheat and rapeseed-wheat), in order to assess the effect of replacing rapeseed by winter pea at the head of the rotation .We evaluated the effect of these two crops (winter pea vs rapeseed) on the biological state of the soil and nitrogen fluxes at different spatio-temporal scales. The results showed a significant spatio-temporal effect on the response of soil microbial communities and highlighted the importance of the pedoclimatic context in determining the abundance and activity of soil microbial communities. A positive effect of winter pea has been demonstrated on the availability of mineral nitrogen during the crop cycle and for following crops (wheat and barley). The supply of nitrogen to the soil is linked to the rhizodeposition of nitrogen via plants roots and the degradation of crop residues after harvest. Our results showed that winter pea exhibited the greatest amount of nitrogen rhizodeposition. However, rhizodeposition did not have a significant impact on rhizospheric microbial communities. Contrary to these observations, the degradation of crop residues significantly modified the composition of bacterial communities linked to their initial biochemical composition. Crop succession including winter pea enriched the soil with mineral nitrogen but simulation with STICS software revealed a nitrogen leaching around of 23 kg N. ha-1 during the cropping cycle. These findings underline the importance of adapting an adequate crop management system, including winter pea, to limit nitrogen losses. The results showed also that wheat yields after winter pea without the use of nitrogen fertilizers were equivalent to those obtained after rapeseed. However, rapeseed required significant nitrogen fertilization. Including winter pea in crop rotation in Normandy region may be a key to enhance productivity, to respond to the challenges of agroecological transition, regional protein autonomy, and to reduce environmental and economic costs, by reducing notably, the costs of fertilizers production and uses