京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19297号 / 工博第4094号 / 新制||工||1631(附属図書館) / 32299 / 京都大学大学院工学研究科都市環境工学専攻 / (主査)教授 米田 稔, 教授 伊藤 禎彦, 准教授 藤川 陽子 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Organic soils are formed as deceased plant and animal wildlife is deposited and decomposed in wet environs. These soils have loose structures, low undrained strengths, and high natural water contents, and require improvement before they can be used as foundation materials. Previous researchers have found that the deep mixing method effectively improves organic soils. This study presents a quantitative and reliable method for predicting the strength of one organic soil treated with deep mixing. For this thesis, organic soils were manufactured from commercially available components. Soil-binder mixture specimens with different values of organic matter content, OM, binder content, water-to-binder ratio, and curing time were tested for unconfined compressive strength (UCS). Least-squares regression was used to fit a predictive equation, modified from the findings of previous researchers, to this data. The equation estimates the UCS of a deep-mixed organic soil specimen using its total water-to-binder ratio and mixture dry unit weight. Soil OM is incorporated into the equation as a threshold binder content, aT, required to improve a soil with a given OM; the aT term is used to calculate an effective total water-to-binder ratio. This thesis reached several important conclusions. The modified equation was successfully fitted to the data, meaning that the UCS of some organic soil-binder mixtures may be predicted in the same manner as that of inorganic soil-binder mixtures. The fitting coefficients from the predictive equations indicated that for the soils and binder tested, specimens of organic soil-binder mixtures have a greater relative gain of UCS immediately after mixing compared to specimens of inorganic soil-binder mixtures. However, the inorganic mixtures generally have a greater relative gain of UCS during the curing period. The influence of curing temperature was found to be similar for organic and inorganic mixtures. For the organic soils and binder tested in this research, aT may be expressed as a linear or power function of OM. For both functions, the value of aT was negligible at values of OM below 45%, which reflects the chemistry of the organic matter in the peat moss. For projects involving deep mixing of organic soils, the predictive equation will be used most effectively by fitting it to the results of bench-scale testing and then checking it against the results of field-scale testing. / Master of Science / Organic soils are formed continuously as matter from deceased organisms – mainly plants – is deposited in wet environs and decomposes. Organic soils are most commonly found in swamps, marshes, and coastal areas. These soils make poor foundation materials due to their low strengths. Deep mixing, or soil mixing, involves introducing a binder like Portland cement or lime into soil and blending the soil and binder together to form columns or blocks. Upon mixing, cementitious reactions occur, and the soil-binder mixture gains strength as it cures. Deep mixing may be performed using either a dry binder, known as dry mixing, or a binder-water slurry, referred to as wet mixing. Deep mixing may be used to treat either inorganic or organic soils to depths of 30 meters or greater. Contractor experience has shown that deep mixing is one of the most effective methods of improving the strength of organic soils. Lab-scale studies (by previous researchers) of wet mixing of inorganic soils have found that the strength of soil-binder mixtures can be expressed as a function of mixture curing time and curing temperature, as well as the quantity of binder used, or binder factor, and the consistency of the binder slurry. No corresponding expression has been generated for wet mixing of organic soils, although many studies on the subject have been performed by previous researchers. The goal of this research was to generate such an expression for one organic soil. The soil used was made of sphagnum peat moss, an organic material commonly found in nature, and an inorganic clay used by previous researchers in studies of deep mixing in inorganic soils. The binder used in this research was a Portland cement. For this research, 43 unique soil-binder mixtures were manufactured. Each mixture involved a unique combination of soil organic matter content, binder factor, and binder slurry consistency. After a soil-binder mixture was made, it was divided, placed into cylindrical molds, and allowed to cure. The temperature of the curing environment of the mixture was monitored. Mixture compressive strength was assessed after 7, 14, and 28 days of curing using two cylindrically molded specimens of the mixture. Data on mixture strength was then evaluated to assess whether it could be expressed as a function of the variables tested. iv This research determined that the strength of at least some organic soils improved with wet mixing can be expressed as a function of soil organic matter content, binder factor, binder slurry consistency, and mixture curing time and curing temperature. The function will likely prove useful to deep mixing contractors, who routinely perform lab-scale deep mixing trials on samples of the soils to be improved in the field. Assuming wet mixing is used, the results of the trials are used to select values of binder factor and binder slurry consistency for the project. The function generated from this research will allow deep mixing contractors to select these values more reliably during the lab-scale phase of their work.

The wet method of deep mixing constructs binder-treated soil columns by mixing a binder-water slurry with soft soil in-situ to improve the engineering properties of the soil. The strength of binder-treated soil is affected by characteristics of the in-situ soil and binder, mixing conditions, and curing conditions.The study presented herein aims to investigate the influences of curing time, curing temperature, mix design proportion, organic matter in the soil, and curing stress on the strength of cement-treated soil. Fabricated and natural soft soils were mixed with a cement-water slurry to mimic soil improved by the wet method of deep mixing. Laboratory-size samples were cured under various curing conditions and tested for unconfined compressive strength (UCS).The experimental test results showed that (1) a higher curing temperature and longer curing time generally increase the strength; (2) organic matter in cement-treated soil decrease and/or delay the strength development; and (3) curing stress affects the strength but its effect is influenced by drainage conditions. Based on the test results, strength-predicting correlations for cement-treated soil that account for various curing conditions and organic contents were proposed and validated.This research contributes to advancing the knowledge about the effects of strength-controlling factors of soil improved by cement and to improving the reliability of strength predictions with the proposed correlations. Therefore, the number of sample batches that need to be prepared and tested in a deep mixing project can be reduced, thereby saving the project's time and costs while achieving the target strength of the improved soil. / Doctor of Philosophy / The deep mixing method has gained popularity in the U.S. as a ground improvement technique since the late 1990s. This method involves blending the native soil that needs to be improved with a binder such as cement and/or lime. Two types of deep mixing methods are available, depending on how to add binder to the soil: the wet method injects a binder-water slurry, while the dry method uses a powder form of binder.The binder reacts with water and soil thereby enhancing the engineering properties of the soil. The strength of binder-treated soil is influenced by many factors: (1) characteristics of native soil and binder; (2) mixing conditions (e.g., the amount of binder added and mixing energy); and (3) curing conditions (e.g., curing time, temperature, and stress). In this dissertation, the effects of curing conditions and organic matter in the soil on the strength of cement-treated soil were investigated. Fabricated and natural soils were mixed with cement-water slurry to simulate the wet method, and the prepared samples were cured under various conditions. The strength results of cured samples showed that the characteristics of cement-treated soil are significantly affected by the amount of cement in the mixture, curing time, curing temperature, organic matter in soil, and curing stress. The test results were also used to derive correlations that account for the influences of curing conditions and organic matter.The findings and strength-predicting correlations presented in this research are expected to improve the knowledge about the deep mixing method and the reliability of strength prediction in a deep mixing project. This research, eventually, contributes to reducing time and cost of the project.

<p>Organic soil depth of burn in Canadian boreal peatlands cited in the literature generally ranges from 0.05 to 0.10 m despite fire manager reports that suggest higher burn severity (> 0.50 cm) may exist on the landscape. It was hypothesized that hydrogeological setting imposes different landscape patterns of peat bulk density and moisture content leading to greater variability in organic soil burn severity across the landscape than previously thought. To examine this, depth of burn was measured in three peatlands located along a hydrogeological and topographic gradient that were affected by the May 2011 Utikuma Complex forest fire (SWF-057, ~90,000 ha) in Canada’s Western Boreal Plain. The results demonstrate that peatland margins, due to fluctuating water tables, burned significantly deeper (0.25 ± 0.01 m) than the middle (0.06 ± 0.01 m) of peatlands. Additionally, in a coarse textured glaciofluvial outwash, a bog with ephemeral groundwater connections had the greatest depth of burn (0.51 ± 0.02 m) and a low-lying flow-through bog had the lowest burn severity (0.07 ± 0.03 m). An expansive peatland in the lacustrine clay plain showed an intermediate depth of burn (0.16 ± 0.01 m). To further investigate the role of groundwater connectivity in the outwash, GWC and smouldering energy dynamics were modelled at several unburned peatlands across a topographic gradient. It was shown that the peatland with the most groundwater connectivity showed the lowest vulnerability, while the ephemerally perched peatland was the most vulnerable. The peatland at the highest topographic position and least groundwater connection showed intermediate vulnerability. This research indicates that groundwater connectivity and subsequent influence on water table fluctuations in peatland margins can have a dominant control on soil carbon combustion, it is therefore suggested that a hydrogeological ‘template’ be used to identify deep burning ‘hotspots’ on the landscape a priori, so as to increase the efficacy of wildfire mitigation strategies.</p> / Master of Science (MSc)

Este trabalho consiste em um estudo para viabilizar o melhoramento de um solo mole orgânico com o uso de cimentação. Foram avaliadas numerosas variáveis, como diferentes agentes cimentantes, distintos materiais juntamente com estes agentes e diferentes temperaturas de cura. Foi desenvolvida uma metodologia de processamento dessas misturas para viabilizar e otimizar a moldagem, cura, desmoldagem e ruptura dos elementos que foram analisados. Os agentes cimentantes utilizados foram a cal viva e o cimento de alta resistência inicial. Juntamente com os agentes cimentantes, foram empregados escória de aciaria, escória de forno panela, fosfogesso e gesso. As temperaturas de cura empregadas foram 20 graus Célsius e 50 graus Célsius. O solo utilizado neste estudo, uma argila mole orgânica com teor de umidade natural variando de 85% a 100%, obtido em Nova Santa Rita, Rio Grande do Sul, foi caracterizado química e fisicamente. Para caracterizá-lo quimicamente foram executados ensaios de perda ao fogo, análise elementar, difratograma de raio X e fracionamento da matéria orgânica. Na faixa de variáveis analisadas, o melhoramento deste material com o uso dos agentes cimentantes utilizados mostrou-se possível, o mais indicado para utilização é o cimento CP-V e quanto maior a dosagem adicionada maior foi a resistência obtida. Com a cal viva, observou-se um teor ótimo, a partir do qual um acréscimo de material gera uma diminuição no ganho de resistência, fato que pode em um projeto real ser prejudicial. As escórias de aciaria e de forno panela não se mostraram eficientes na avaliação do ganho de resistência quando utilizadas com os agentes cimentantes analisados neste material. O gesso e o fosfogesso proporcionaram um ganho de resistência considerável à mistura quando utilizados junto com o cimento CP-V, principalmente para altas dosagens, já com cal tiveram um efeito extremamente prejudicial, fazendo o ganho de resistência da mistura solo/cal viva cair em até 50%. A temperatura de cura mostrou-se eficaz na aceleração das reações pozolânicas tanto para a cal quanto para o cimento. Foi possível adaptar uma metodologia de dosagem em função do fator porosidade/teor volumétrico de cimento apenas para as misturas solo/cimento. / The focus of this study is enabling the improvement of an organic soft soil by means of pozzolanic reaction. A several variables were evaluated, such as type of stabilization, pure or mixed with other materials and two distinct curing temperatures. In order to facilitate and optimize the molding, curing, unmolding and rupture of the specimens, a methodology was developed for processing the mixtures. The binding agents used were cement and quicklime. Mixed with the binding agents, electric arch furnace slag, ladle furnace slag, gypsum and phosphoric gypsum were added. The used curing temperatures were 20 and 50 degrees Celsius. The soil used in this study is a very soft organic clay with natural moisture content ranging from 85% to 100% obtained in Nova Santa Rita, Rio Grande do Sul, Brazil. It was chemically and physically characterized. The chemical characterization consisted of loss of ignition tests, elemental analysis, X-ray diffraction and the fractionation of organic matter. The improvement of this material with the use of the previously mentioned binders proved possible within the range of variation of the analyzed variables. The best results were obtained when using cement, and the larger the content of cement the greater the added strength. As for the quicklime, an optimum lime content was observed. From this optimum point onwards any addition of quicklime will result in diminishment of the gained strength as such, when utilizing this method in a real project, one must be aware of this diminishment so as to avoid detrimental results. Utilized with the binding agents analyzed in this material, the electric arc furnace slag and the ladle slag were shown to be inefficient when evaluating the gain of strength. Gypsum and phosphoric gypsum led to considerable gain in strength when mixed with cement, especially in high dosages. When mixed with quicklime, however, the effect was a drop of up to 50% in the gain of strength. The curing temperature was effective in accelerating pozzolanic reactions for both the cement and the quicklime. It was possible to adapt a dosing methodology using the function porosity/volumetric cement content into soil/cement mixtures.

Este trabalho consiste em um estudo para viabilizar o melhoramento de um solo mole orgânico com o uso de cimentação. Foram avaliadas numerosas variáveis, como diferentes agentes cimentantes, distintos materiais juntamente com estes agentes e diferentes temperaturas de cura. Foi desenvolvida uma metodologia de processamento dessas misturas para viabilizar e otimizar a moldagem, cura, desmoldagem e ruptura dos elementos que foram analisados. Os agentes cimentantes utilizados foram a cal viva e o cimento de alta resistência inicial. Juntamente com os agentes cimentantes, foram empregados escória de aciaria, escória de forno panela, fosfogesso e gesso. As temperaturas de cura empregadas foram 20 graus Célsius e 50 graus Célsius. O solo utilizado neste estudo, uma argila mole orgânica com teor de umidade natural variando de 85% a 100%, obtido em Nova Santa Rita, Rio Grande do Sul, foi caracterizado química e fisicamente. Para caracterizá-lo quimicamente foram executados ensaios de perda ao fogo, análise elementar, difratograma de raio X e fracionamento da matéria orgânica. Na faixa de variáveis analisadas, o melhoramento deste material com o uso dos agentes cimentantes utilizados mostrou-se possível, o mais indicado para utilização é o cimento CP-V e quanto maior a dosagem adicionada maior foi a resistência obtida. Com a cal viva, observou-se um teor ótimo, a partir do qual um acréscimo de material gera uma diminuição no ganho de resistência, fato que pode em um projeto real ser prejudicial. As escórias de aciaria e de forno panela não se mostraram eficientes na avaliação do ganho de resistência quando utilizadas com os agentes cimentantes analisados neste material. O gesso e o fosfogesso proporcionaram um ganho de resistência considerável à mistura quando utilizados junto com o cimento CP-V, principalmente para altas dosagens, já com cal tiveram um efeito extremamente prejudicial, fazendo o ganho de resistência da mistura solo/cal viva cair em até 50%. A temperatura de cura mostrou-se eficaz na aceleração das reações pozolânicas tanto para a cal quanto para o cimento. Foi possível adaptar uma metodologia de dosagem em função do fator porosidade/teor volumétrico de cimento apenas para as misturas solo/cimento. / The focus of this study is enabling the improvement of an organic soft soil by means of pozzolanic reaction. A several variables were evaluated, such as type of stabilization, pure or mixed with other materials and two distinct curing temperatures. In order to facilitate and optimize the molding, curing, unmolding and rupture of the specimens, a methodology was developed for processing the mixtures. The binding agents used were cement and quicklime. Mixed with the binding agents, electric arch furnace slag, ladle furnace slag, gypsum and phosphoric gypsum were added. The used curing temperatures were 20 and 50 degrees Celsius. The soil used in this study is a very soft organic clay with natural moisture content ranging from 85% to 100% obtained in Nova Santa Rita, Rio Grande do Sul, Brazil. It was chemically and physically characterized. The chemical characterization consisted of loss of ignition tests, elemental analysis, X-ray diffraction and the fractionation of organic matter. The improvement of this material with the use of the previously mentioned binders proved possible within the range of variation of the analyzed variables. The best results were obtained when using cement, and the larger the content of cement the greater the added strength. As for the quicklime, an optimum lime content was observed. From this optimum point onwards any addition of quicklime will result in diminishment of the gained strength as such, when utilizing this method in a real project, one must be aware of this diminishment so as to avoid detrimental results. Utilized with the binding agents analyzed in this material, the electric arc furnace slag and the ladle slag were shown to be inefficient when evaluating the gain of strength. Gypsum and phosphoric gypsum led to considerable gain in strength when mixed with cement, especially in high dosages. When mixed with quicklime, however, the effect was a drop of up to 50% in the gain of strength. The curing temperature was effective in accelerating pozzolanic reactions for both the cement and the quicklime. It was possible to adapt a dosing methodology using the function porosity/volumetric cement content into soil/cement mixtures.

Este trabalho consiste em um estudo para viabilizar o melhoramento de um solo mole orgânico com o uso de cimentação. Foram avaliadas numerosas variáveis, como diferentes agentes cimentantes, distintos materiais juntamente com estes agentes e diferentes temperaturas de cura. Foi desenvolvida uma metodologia de processamento dessas misturas para viabilizar e otimizar a moldagem, cura, desmoldagem e ruptura dos elementos que foram analisados. Os agentes cimentantes utilizados foram a cal viva e o cimento de alta resistência inicial. Juntamente com os agentes cimentantes, foram empregados escória de aciaria, escória de forno panela, fosfogesso e gesso. As temperaturas de cura empregadas foram 20 graus Célsius e 50 graus Célsius. O solo utilizado neste estudo, uma argila mole orgânica com teor de umidade natural variando de 85% a 100%, obtido em Nova Santa Rita, Rio Grande do Sul, foi caracterizado química e fisicamente. Para caracterizá-lo quimicamente foram executados ensaios de perda ao fogo, análise elementar, difratograma de raio X e fracionamento da matéria orgânica. Na faixa de variáveis analisadas, o melhoramento deste material com o uso dos agentes cimentantes utilizados mostrou-se possível, o mais indicado para utilização é o cimento CP-V e quanto maior a dosagem adicionada maior foi a resistência obtida. Com a cal viva, observou-se um teor ótimo, a partir do qual um acréscimo de material gera uma diminuição no ganho de resistência, fato que pode em um projeto real ser prejudicial. As escórias de aciaria e de forno panela não se mostraram eficientes na avaliação do ganho de resistência quando utilizadas com os agentes cimentantes analisados neste material. O gesso e o fosfogesso proporcionaram um ganho de resistência considerável à mistura quando utilizados junto com o cimento CP-V, principalmente para altas dosagens, já com cal tiveram um efeito extremamente prejudicial, fazendo o ganho de resistência da mistura solo/cal viva cair em até 50%. A temperatura de cura mostrou-se eficaz na aceleração das reações pozolânicas tanto para a cal quanto para o cimento. Foi possível adaptar uma metodologia de dosagem em função do fator porosidade/teor volumétrico de cimento apenas para as misturas solo/cimento. / The focus of this study is enabling the improvement of an organic soft soil by means of pozzolanic reaction. A several variables were evaluated, such as type of stabilization, pure or mixed with other materials and two distinct curing temperatures. In order to facilitate and optimize the molding, curing, unmolding and rupture of the specimens, a methodology was developed for processing the mixtures. The binding agents used were cement and quicklime. Mixed with the binding agents, electric arch furnace slag, ladle furnace slag, gypsum and phosphoric gypsum were added. The used curing temperatures were 20 and 50 degrees Celsius. The soil used in this study is a very soft organic clay with natural moisture content ranging from 85% to 100% obtained in Nova Santa Rita, Rio Grande do Sul, Brazil. It was chemically and physically characterized. The chemical characterization consisted of loss of ignition tests, elemental analysis, X-ray diffraction and the fractionation of organic matter. The improvement of this material with the use of the previously mentioned binders proved possible within the range of variation of the analyzed variables. The best results were obtained when using cement, and the larger the content of cement the greater the added strength. As for the quicklime, an optimum lime content was observed. From this optimum point onwards any addition of quicklime will result in diminishment of the gained strength as such, when utilizing this method in a real project, one must be aware of this diminishment so as to avoid detrimental results. Utilized with the binding agents analyzed in this material, the electric arc furnace slag and the ladle slag were shown to be inefficient when evaluating the gain of strength. Gypsum and phosphoric gypsum led to considerable gain in strength when mixed with cement, especially in high dosages. When mixed with quicklime, however, the effect was a drop of up to 50% in the gain of strength. The curing temperature was effective in accelerating pozzolanic reactions for both the cement and the quicklime. It was possible to adapt a dosing methodology using the function porosity/volumetric cement content into soil/cement mixtures.

Orientadores: David de Carvalho, João Alexandre Paschoalin Filho / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Agrícola / Made available in DSpace on 2018-08-20T20:09:47Z (GMT). No. of bitstreams: 1 Moretti_GeraldoVanzolini_M.pdf: 6241901 bytes, checksum: 46aab2abefeeaa620ad785d7e3752122 (MD5) Previous issue date: 2012 / Resumo: Apresenta-se neste trabalho o estudo comportamento à compressão não confinada de um solo argiloso aluvionar estabilizado segundo a metodologia Deep Soil Mixing (DSM). Esta técnica consiste no tratamento de solos moles através da mistura deste com agentes químicos estabilizantes, podendo-se utilizar cal e/ou cimento. Para a condução deste trabalho foram executadas colunas de DSM sob um aterro rodoviário localizado no nordeste do Brasil, com aproximadamente 300m de extensão. O sítio de estudo é caracterizado por apresentar superficialmente uma camada homogênea composta por uma argila-siltosa orgânica de consistência mole a muito mole e coloração acinzentada com espessura variando entre 12 e 15m. O nível do lençol freático foi encontrado superficialmente a uma profundidade de 1,60m. As colunas possuíam diâmetro de 0,80m e foram executadas em campo utilizando-se como agente estabilizador Cimento Portland CPII-E32, com dosagem de 600kg/m3 e relação água cimento a/c=0,8. Após execução das colunas, foram coletados corpos de prova de seu interior, em profundidades variáveis, por meio da utilização de equipamento de sondagem rotativa. Os corpos de prova foram posteriormente encaminhados ao laboratório, onde foram conduzidos ensaios de compressão simples não confinada. Um programa de ensaios de campo e laboratório também foi conduzido de forma a caracterizar o subsolo local. Para tal foram conduzidos ensaios de simples caracterização geotécnica e ensaios "in situ", tais como Ensaios de Palheta (Vane Test), CPTU e Sondagens SPT (Standard Penetration Test). Foram também coletadas amostras de argila mole local no intuito de se proceder a sua estabilização em laboratório. As amostras foram misturadas em três diferentes dosagens de cimento, 200kg/m3, 400kg/m3 e 600kg/3 e todas com relação a/c=0,8. A análise dos dados, determinados através dos ensaios conduzidos, possibilitou a constatação do ganho de resistência à compressão simples da mistura de solo/cimento com o tempo, além da influência da dosagem na mobilização e na magnitude das resistências obtidas. Estes também possibilitaram identificar que a resistência à compressão simples dos corpos de prova moldados em laboratório geralmente apresentam-se superiores aos valores obtidos a partir dos corpos de prova coletados "in loco" no interior das colunas executadas / Abstract: It is presented in this work the study the behavior of unconfined compressive soilcement columns using the methodology Deep Soil Mixing (DSM). This technique consists in the treatment of soft soils mixing them with chemical stabilizers, such as lime or cement. To conduct this work were executed DSM columns in a embankment road located in northeastern Brazil, with approximately 300m in length. The local subsoil is characterized by presenting a superficially homogeneous layer composed of an organic clay-silt to very soft consistency of soft gray color with a thickness ranging between 12 and 15m. The groundwater level is found at 1.60m depth. The columns had a diameter of 0.80 m. These were performed using Portland cement CPII-E32 as a stabilizing agent. There were used the following dosage of 600kg/m3 and cement ratio 0,8. Specimens were collected each studied column, in different depths through the use of rotary drilling equipment. The specimens were subsequently sent to the laboratory, where were conducted unconfined compressive tests. A program of field and laboratory tests were also conducted aiming to characterize the local subsoil, such as geotechnical characterization tests, Vane Test, CPTU and SPT (Standard Penetration Test). Samples of soft clay were also collected aiming to carry out their stabilization in the laboratory by cement adding. The samples were mixed in the same dosages used to make the columns in the field. The obtained parameters showed the gain of the compressive strength of the stabilized soil samples with time increasing in different dosages. There were also identified that the compressive strength of the specimens molded in the laboratory is usually higher than the values obtained from specimens collected "in situ" inside the columns / Mestrado / Construções Rurais e Ambiencia / Mestre em Engenharia Agrícola

L’affaissement et la dégradation des sols organiques, utilisés pour les cultures maraîchères du Québec, sont actuellement des sujets criants. Ces sols très fertiles sont utilisés pour la production d’environ 50 % des légumes au Québec. Cependant, une partie de cette ressource est perdue, à chaque année, à cause de l’érosion et de l’activité microbienne. Plusieurs mesures sont actuellement prises pour réduire ces pertes, telles que l’utilisation de brise-vent et la réduction des labours, dans le but d’augmenter la durée de vie de cette ressource. Toutefois, ces méthodes ne sont pas suffisantes et ne considèrent pas les facteurs biotiques derrière la dégradation des sols organiques. La respiration (oxydation) microbienne représente pourtant plus de 50 % de la perte totale de matière organique dans le sol. Comme les nématodes libres sont les prédateurs principaux du microbiote, leur abondance et leur diversité pourraient influencer les populations microbiennes, mais les conséquences de cette interaction sur la composition et la diversité des communautés sont peu connues. Cette étude fait ressortir le rôle indirect des nématodes dans la dégradation de la matière organique via la prédation des bactéries et des champignons dans le sol et la régulation de ces communautés. Nous avons manipulé les communautés de nématodes afin d’observer des variations de composition et de diversité dans la communauté bactérienne, ainsi que dans les processus de dégradation de la matière organique. Des variations significatives ont été observées pour la production possible d’enzymes extracellulaires provenant des bactéries, l’abondance des bactéries, la disponibilité de l’azote dans le sol et le rendement des feuilles de laitues. Ces résultats permettent de faire ressortir l’importance de la prédation des nématodes et la nécessité d’accorder à ce groupe une plus grande attention dans la mise en place de systèmes de production végétale. L’ajustement des pratiques culturales pourrait aider à maintenir des réseaux écologiques plus stables et augmenter la longévité des sols organiques. / The subsidence and degradation of organic soils, used for vegetable crops in Quebec, is currently a critical issue. These very fertile soils are used for the production of about 50% of the vegetables in Quebec. However, part of this resource is lost every year due to erosion and microbial activity. Several measures are currently being taken to reduce these losses, such as the use of windbreaks and the reduction of plowing, to increase the life span of this resource. However, these methods are not sufficient and do not consider the biotic factors behind organic soil degradation. Microbial respiration (oxidation) accounts for more than 50% of the total loss of organic matter in the soil. Free-living nematodes are the main predators of the microbiota, their abundance and diversity could influence microbial populations, but the consequences of this interaction on community composition and diversity are poorly understood. This study highlights the indirect role of nematodes in the degradation of organic matter via predation of bacteria and fungi in the soil and the regulation of these communities. We manipulated nematode communities and observed variations in composition and diversity in the bacterial community, as well as in organic matter degradation processes. Specifically, significant variations were obtained for the possible production of extracellular enzymes from bacteria, bacterial abundance, soil nitrogen availability, and lettuce leaf yield. These results serve to highlight the importance of nematode predation and the need for greater attention to this group in the development of crop production systems. Adjusting cultural practices could help maintain more stable ecological networks and increase the longevity of organic soils.

Peatlands in the sub-humid Boreal Plains of Alberta exist at the limit of their climatic tolerance and are vulnerable to wildfire. This is especially true at the interface between the peatland and forestland (margins) due to water table fluctuation resulting in high peat bulk density and low moisture content during dry periods in some peatland systems. Deep burning at the margins may reduce a peatland's ability to recover to its previous state, leading to a reduction in area and/or collapse following fire, and bringing into question the long-term stability of Boreal Plains peatlands on the landscape under current and future climate predictions. Previous research has identified small peatlands located at a mid-topographic position on coarse sediments as hotspots for deep burning, as these peatlands are not regularly connected to regional groundwater flow. The ability of these peatland systems to recover lost carbon from both the interior and margin within the fire return interval, however, has not yet been investigated. This thesis further examines the relationship between surficial sediment assemblages and the impact of wildfire on overlying peatlands through assessment of organic soil carbon accumulation following wildfire across the Boreal Plains landscape. Peatland organic soil recovery along a chronosequence was assessed in the interior and margin of 26 ombrotrophic bogs located at various positions on the post-glaciation landscape of Northern Alberta using estimates of organic soil carbon accumulation calculated through loss on ignition of peat above the uppermost charcoal layer in peat cores from each site, as well as characterization of peat properties along a transect from the adjacent forestland into the peatland interior. Soil organic carbon accumulation with time since fire was greater in studied peatland interiors than margins. Underlying sediments were found to have little effect on total soil organic carbon accumulation in the interior and margins of the studied peatlands, indicating that organic soil carbon accumulation rates following wildfire estimated in this study can be extended to ombrotrophic bogs across the Boreal Plains landscape. Though total soil organic carbon accumulation following wildfire does not appear to be influenced by hydrogeological setting, the ability of a peatland to recover the quantity of carbon lost within the fire return interval will be dependent on the amount of carbon which was released through smouldering, which is influenced by hydrogeological setting for peatland margins. Based on published measurements of organic soil carbon loss during wildfire and organic soil carbon accumulation rates estimated in this thesis, peatlands located at topographic lows on coarse grained glaciofluvial outwash sediments or on low-relief, fine grained sediment deposits from glaciolacustrine or subglacial paleoenvironments are predicted to be resilient to wildfire on the Boreal Plains landscape. Peatlands which experience severe smouldering at the margins, such as ephemerally perched systems on glaciofluvial outwash sediments, will likely undergo permanent loss of legacy carbon stores. The resilience of peatlands which are perched above regional groundwater on glaciofluvial outwash or stagnant ice moraine deposits is unknown at this time; further investigation into water table dynamics, margin peat properties, and smouldering depths in these systems is required. Identification of peatland systems which are at risk of permanent carbon loss at the margins and those which are most resilient to wildfire in this thesis can be applied to wildfire management strategies and the design of peatland systems for reclamation of oil sands leases. The stability of natural and created peatlands through time on a landscape where wildfire is frequent is an important consideration in terms of both lasting ecosystem services and the potential risk to fire suppression and community safety that vulnerable systems pose. / Thesis / Master of Science (MSc)