学位授与大学：京都大学 ; 取得学位: 博士(工学) ; 学位授与年月日: 2007-09-25 ; 学位の種類: 新制・課程博士 ; 学位記番号: 工博第2841号 ; 請求記号: 新制/工/1418 ; 整理番号: 25526 / The consolidation of peat is complex due to the resultant large strain associated with the highly compressible nature of natural peat deposits and to the rapid changes in soil properties during the consolidation process. In addition, the consolidation process is further complicated by the occurrence of secondary compression which significantly contributes to the overall settlement of peaty soil. Therefore, it is necessary to take these properties into account in order to obtain better predictions from peat consolidation analyses. In the present study, the consolidation behavior of peaty clay found in Sri Lanka is extensively studied using a model based on the elasto-viscoplastic theory. The model can describe the prominent creep behavior of peaty soil as a continuous process. In addition, the model can accommodate the effect of structural degradation on the consolidation process. The analysis takes into account all the main features involved in the peat consolidation process, namely, finite strain, variable permeability, and the effect of secondary compression. Also, it considers the variable compressibility for stage-constructed embankments which exert high levels of pressure on the peaty subsoil. The constitutive equations used in the model and the procedure adapted to account for the above-mentioned features of the analysis are described. The constitutive model is based on Perzyna’s type viscoplastic theory and the Cambridge elasto-plastic theory combined with empirical evidence. In the finite element formulations, which are based on the finite deformation theory, an updated Lagrangian method is adopted. A description of the material parameters used in the model and the procedures applied to evaluate them, with standard laboratory and field tests, are explained. In addition, a performance of the model incorporating the original and the modified Cam-clay theory is evaluated by simulating triaxial test results. A comparison shows that with the present definition of the parameters, the original model yields more representative results than the model based on the modified Cam-clay theory. Initially, the capability of the constitutive model to capture the consolidation behavior is verified using the consolidation model test data on peaty clay found in Sri Lanka. It is confirmed that the constitutive model is able to predict the observed creep characteristics and the effect of sample thickness on settlement predictions for the material under consideration. The performance of the model in predicting the consolidation behavior under field conditions is studied using field data on instrumented earth fill constructed on peaty clay. One-dimensional compression is assumed for the peaty clay due to the large plane area of the fill. Separate analyses are carried out by the model considering the infinitesimal strain theory, the finite strain theory, and the finite strain theory together with the effect of structural degradation in order to explore how these features describe the observed field behavior. Analyses reveal that it is necessary to consider finite deformation together with the effect of structural degradation in order to successfully simulate the resultant large strain and the stagnated pore water pressure observed in the field. The construction of road embankments over peat deposits is quite problematic, and thus, it is often done after first improving the properties of the peaty soil through the utilization of appropriate ground-improvement techniques. Understanding the field response of peaty clay during this improvement process is naturally of great importance. A constitutive model is applied to predict the field performance of embankments constructed on peaty clay using different ground-improvement techniques. The back analysis of embankments constructed with the preloading method indicates that the model can be successfully applied to predict both the deformation and the stability of structures constructed on peaty clays. The stability of the embankment during and after construction is verified by investigating the stress-strain characteristics of the subsoil. The model applications used to predict the consolidation behavior of embankments constructed by the preloading method, combined with other ground-improvement techniques, are then discussed. Embankments constructed with prefabricated vertical drains (PVDs) and sand compaction piles (SCPs) are considered, and finite element analyses are carried out in all cases by converting the actual three-dimensional conditions that exist around the drains into simplified two-dimensional plane strain conditions. The field behavior when PVDs are installed in the peaty clay is simulated using the equivalent vertical permeability for the PVD-improved subsoil. In the case of SCPs, a conversion scheme is used to transform the axisymmetric nature of sand columns into equivalent plane strain conditions. A comparison of the predicted results with the field observations shows a reasonable agreement. An analysis of the PVD-improved foundation indicates that the installation of PVDs not only accelerates the rate of consolidation, but influences the deformation pattern of the subsoil due to embankment loading. The analysis also shows that the use of PVDs can significantly increase embankment stability. The model prediction for the SCP-improved foundation reveals that the stiffness and the area replacement ratio used in the conversion scheme play vital roles in predicting the behavior of SCP-improved soft grounds. The observed improvements in the bearing capacity of the subsoil and in the stability of the embankment, brought about by the installation of SCPs, can be simulated by the model. / Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第13370号 / 工博第2841号 / 新制||工||1418(附属図書館) / 25526 / UT51-2007-Q771 / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 岡 二三生, 教授 田村 武, 准教授 木元 小百合 / 学位規則第4条第1項該当

Conselho Nacional de Desenvolvimento Científico e Tecnológico / In areas managed under no-till in southern Brazil the soil compaction process has been associated with structural degradation of subsurface soil layer, visible by changes in soil physical properties, morphological changes of roots and casual perception of crop yield reduction. As an alternative to mitigate this process or to prevent the soil reaches critical levels of compaction, farmers use mechanical chiseling to promote the disruption of the compacted layer and improve soil structure. However, the benefits of this practice on soil physical and hydraulic properties have shows short duration making necessary to search for alternative methods to mitigate soil compaction. In this sense, this paper aims to study the duration of the benefits of mechanical chiseling on physic-hydraulic soil properties, aiding in the understanding of soil reconsolidation time and the development of strategies to mitigate compaction based on the types of fertilizer furrow in the no-till seeders. Therefore, a study was conducted in Coxilha, in northern region of the Rio Grande do Sul state on an Oxisol, to assess the residual effect of chiseling. The treatments were composed by the control treatment (27 years under continuous no-till) and seven adoption times (0, 6, 12, 18, 24, 30 and 36 months) of no-till after mechanical chiseling. To assess the potential to mitigate soil compaction of the seeder furrow were evaluated three strategies: shanks plus disc to 0.10 m; shanks plus disc to 0.15 and double disc to 0.07 m depth. The treatments were compared by the soil physical and hydraulic properties of bulk density, relative density, pore distribution, penetration resistance, infiltration rate, water retention capacity, water store for plants, saturated hydraulic conductivity, unsaturated hydraulic conductivity and air permeability. The results indicated that the residuality of mechanical chiseling varies according to the evaluated physical-hydraulic attribute lasting only for one harvest to the bulk density, total porosity and macroporosity, 18 months for penetration resistance and 24 months for hydraulic conductivity and infiltration rate. There was no residual effect of chiseling for time periods longer than two years after tillage. The use of furrow shank type to 0.15 m deep, promoted the disruption of compacted layer with very similar benefits to those obtained with soil chiseling, indicating potential to use to mitigate soil compaction under no-till systems. / Em áreas manejadas sob sistema plantio direto (SPD) na região Sul do Brasil o processo de compactação tem sido associado a degradação estrutural da camada subsuperficial do solo, perceptível, por alterações de atributos físicos do solo, alterações morfológicas de raízes e percepção, ocasional, de redução da produtividade das culturas. Como alternativa para mitigar esse processo ou para prevenir que o solo atinja níveis críticos de compactação, produtores utilizam a escarificação mecânica para promover o rompimento da camada compactada e melhorar a estrutura do solo. Contudo, os benefícios advindos dessa prática sobre propriedades físico-hídricas do solo têm apresentado duração efêmera, o que conduz a procura por métodos alternativos de mitigação do estado de compactação do solo. Nesse sentido, o presente trabalho visa estudar a duração dos benefícios da escarificação mecânica sobre propriedades físico-hídricas do solo, auxiliando na compreensão do tempo de reconsolidação do solo e no desenvolvimento de estratégias de mitigação do estado de compactação baseadas no mecanismo sulcador da semeadora. Para tanto, foi realizado um estudo no município de Coxilha, na região norte do Rio Grande do Sul sob Latossolo Vermelho Distrófico típico, para avaliar o efeito residual da escarificação. Os tratamentos foram compostos pela testemunha (27 anos sob SPD contínuo) e sete períodos (0, 6, 12, 18, 24, 30 e 36 meses) de adoção do SPD após escarificação. Para determinar o potencial de mitigação do estado de compactação dos sulcadores da semeadora foram avaliadas três estratégias de semeadura: disco de corte+haste sulcadora atuando a 0,10 m; disco de corte+haste sulcadora atuando a 0,15 m; e discos duplos defasados atuando a 0,07 m de profundidade. Os tratamentos foram comparados pelas propriedades físico-hídricas do solo: densidade, densidade relativa, porosidade total, macro e microporosidade, resistência à penetração, taxa de infiltração, retenção de água, água disponível para as plantas, condutividade hidráulica do solo saturado e solo não saturado e permeabilidade ao ar. Os resultados obtidos indicaram que o efeito residual da escarificação mecânica varia conforme a propriedade físico-hídrica avaliada sendo de apenas uma safra agrícola para a densidade, porosidade total e macroporosidade, 18 meses para resistência a penetração e de 24 meses para condutividade hidráulica e a infiltração de água no solo. Não houve efeito residual da escarificação para períodos superiores há dois anos. A utilização de semeadora com haste sulcadora, quando operando a 0,15 m de profundidade, promoveu o rompimento da camada compactada com benefícios muito similares aos obtidos com a escarificação do solo, denotando potencial de utilização para mitigação do estado de compactação do solo sob SPD.

Das litorale Makrozoobenthos ist eine bedeutende biotische Komponente in Seen und trägt substantiell zur Biodiversität und Funktion von Seeökosystemen bei. Allerdings unterliegt das Litoral zunehmenden anthropogenen Nutzungen, deren ökologische Auswirkungen jedoch kaum quantifiziert wurden. In dieser Doktorarbeit wurde untersucht, welche Bedeutung maßgebliche Umweltfaktoren auf die Zusammensetzung des litoralen Makrozoobenthos haben, und wie sich anthropogene Nutzungen auf die Zusammensetzung und Funktion des Makrozoobenthos auswirken. Die Zusammensetzung des Makrozoobenthos wurde durch die Uferstruktur, Trophie und das hydrodynamische Regime bestimmt. Die faunistische Ähnlichkeit zwischen Habitaten war jedoch signifikant geringer als zwischen Trophiestufen, so dass die Uferstruktur, und nicht die Trophie, einen größeren Einfluss auf das Makrozoobenthos hat. Strukturelle Degradation führte zu einer Reduktion der Habitatheterogenität, was eine signifikante Verringerung der Diversität und eine signifikant veränderte Artenzusammensetzung verursachte. Infolgedessen war die Komplexität der Makrozoobenthos-Nahrungsnetze an degradierten Ufern signifikant geringer als an natürlichen Ufern. Erhöhte Wasserstandsschwankungen führten zum Ausfall von Wurzelhabitaten und der damit assoziierten Makrozoobenthos-Gemeinschaft. Schiffsinduzierter Wellenschlag führte zur Verdriftung des Makrozoobenthos von ihren Habitaten bereits bei geringen Sohlschubspannungen. Die Effekte von Wasserstandsschwankungen und schiffsinduziertem Wellenschlag wurden jedoch durch Habitate mit hoher struktureller Komplexität verringert. Mit dieser Doktorarbeit konnte ich ein mechanistisches Verständnis darüber erarbeiten, wie anthropogene Nutzungen die Wirkungsbeziehungen zwischen Umweltfaktoren und Artengemeinschaften verändern und welche ökologischen Auswirkungen dies hat. Diese Kenntnisse können als wissenschaftliche Basis zur Bewertung von anthropogenen Beeinträchtigungen des Litorals dienen. / Littoral macroinvertebrates are an important biotic component of lakes by contributing substantially to the biodiversity and functioning of lake ecosystems. Humans alter the littoral and riparian areas for various purposes, but the resulting ecological impacts on littoral macroinvertebrates have not been quantified. In this thesis, I investigated the significance of key environmental factors for littoral macroinvertebrate communities and how human alterations of these environmental factors impact the structure and function of macroinvertebrate communities. Macroinvertebrate community composition was significantly related to littoral structure, trophic state and the hydrodynamic regime. The significantly higher compositional dissimilarities among habitats than among trophic state suggested that littoral structure was the more important driver of community composition. Structural degradation caused a significant reduction of habitat heterogeneity and resulted in a significant reduction of species diversity and a significant altered community composition. This caused a significant reduction of macroinvertebrate food web complexity and substantial alterations of the trophic base of the food webs. Climate-change induced water level fluctuations resulted in the loss of root habitats and the specific community associated with this habitat. Ship-induced waves had substantial direct effects, since macroinvertebrates were detached from their habitats by waves even at moderate shear stress levels. However, the impacts of water level fluctuations and ship-induced waves were mitigated by the presence of habitats with high structural complexities. This thesis provided a mechanistic understanding of how human activities alter relationships between environmental factors and biotic communities. This knowledge can be used to develop scientifically sound approaches to assess the persistent human impacts on lake ecosystems.