Dissertations / Theses on the topic 'Wetting-Drying cycles'

Thaumasite form of sulfate attack is having great attention since its discovering in series of foundations supporting motorway bridges in the UK in the late nineties of the last century. This is mainly due to its destructive effect on concrete structures, and the lack of information about its formation mechanisms. This research conducted a study on the effect of wetting and drying, carbonation and the effect of water to cement ratio on the thaumasite formation, and whether these effects are linked with other parameters such as cement type and sulfate concentration or not. 10 different mixes were produced based on four binder types in this study namely 100% CEM I, 90% CEM I + 10% Limestone filler, 50% CEM I + 50 %PFA and 30% CEM I +70%GGBS. A series of mortar samples of two types were prepared 50 mm cubes and 40 × 40 × 160 mm prisms. The samples were kept in three different solutions contain BRE DS3,DS4 based on magnesium sulfate MgSO4.7H2O in addition to deionised water. Two different temperatures 5°C and 20°C were also used to confirm the formation of thaumasite at ambient temperatures (20°C) and to accelerate its formation at 5°C. The effect of wetting and drying cycles on thaumasite formation was studied and compared with samples immersed continuously in the same solutions for 12 months. Powder-sulfate interaction and its effect on thaumasite formation was studied by grinding mortar samples to a fine powder, thus eliminating the permeability effect and enabling physical factors that affect the rate at which solutions can be transferred through the mortar to be separated from chemical factors that affect the rate at which the chemical reactions take place. Visual observations, mass and length changes were used to assess the mortar deterioration, along with X-ray diffraction, infra-red spectroscopy and SEM that were used to determine the mineralogy of deterioration products. For the cyclic wetting and drying exposure regime the results showed that wetting and drying cycles significantly delayed thaumasite formation compared with control specimens. For powder samples, it is found that thaumasite is readily formed in these powders after 3 months of exposure to sulfate solutions including GGBS and PFA samples, on the other hand cubes and prisms, exposed to the same solutions for 24 months showed no signs of deterioration. Thermodynamic modelling was used to predict the deterioration products for powders samples and good agreement between predicted and observed results was found.

Decommissioning hydro-dams increases sediment exposure to air, altering biogeochemical cycling of metals. Hg and MeHg mobility was studied in reservoir sediments from two Eastern Ontario lakes (Stump (SL) and Black Donald (BDL)) submitted to wet/dry cycles with artificial rainwater (pH∼4.5) every two weeks. Leachate pH, sulphate, sulphide and MeHg, and sulphate-reducing bacteria (SRB) populations were monitored over 6 months. The sediments did buffer the rainwater at the start of the experiment, but leachate pH decreased over time for both lakes. MeHg release occurred during the first draining event (2-4 ppt), and decreased thereafter, with no relationship with pH, sulphide and sulphate. SRB populations remained constant over time. Over 70% of Hg was in the non-labile refractory organic and residual phases, where Hg moved to semi-mobile phases in SL, but shifted to more immobile phases in BDL over time. Decommissioning hydro-dam reservoirs may increase acid production and alter Hg partitioning in sediments, while MeHg release will be low.

Water level changes due to the decommissioning of hydro-electric dams can result in sediment exposure to air. Oxidation of sediments can decrease the pH as a result of iron sulfides changing into iron oxides. The present study was designed to simulate drying and wetting cycles of shallow lake sediments from two lakes (Stump and Black Donald Lakes in Ontario), in order to assess the mineralogical changes of Fe-rich minerals. Our results indicate that the total reactive iron fraction of the sediment increased after the wetting and drying cycles. This increase was caused by the weathering of pyrite and Fe-silicates and their subsequent transformation into more Fe-reactive mineral species. The pH of the surface sediments also decreased following the addition of simulated rainwater and the oxidation of iron sulfides in the sediments. This preliminary study shows that the decommissioning of hydro-electric dams will have an effect on the biogeochemical cycles of iron and sulfur.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior
The Coastal Plains exhibit cohesive soils, which can cause physical impediments to root penetration and water dynamics. However, in the genesis of these horizons are not completely understood. Thus, the aim of the present study was to evaluate the influence of amorphous compounds in the genesis of cohesive horizons in soils of different textures of the Coastal Plains of CearÃ, as well as verify, through physical behavior of these soils in the presence and absence of these compounds. This study also aimed to evaluate the influence of wetting and drying cycles in the density of these soils. To evaluate the effect of amorphous compounds in soil cohesion, we used samples from the air-dried cohesive horizons 9 soil profiles of the state of CearÃ, these being subjected to two treatments: with and without extraction of amorphous compounds. The samples (with and without extraction) were subjected to 3 cycles of wetting and drying, and subsequently, the penetration resistance (PR), hydraulic conductivity and bulk density were determined. To assess the influence of wetting and drying cycles in the density of these soils were performed 3 different levels of wetting and drying cycles (3, 6, 9 cycles). After these cycles, penetration resistance resistance and density were evaluated. The additions of silica and aluminum low crystalline (amorphous) in cohesive soils show that these compounds contribute jointly in the genesis of these horizons. Regardless of texture, soil that passed through the extraction process of amorphous compounds showed a significant reduction in soil resistance to penetration and density. It was found that these soils, the hydraulic conductivity was higher than that observed in soil without extraction of amorphous compounds. Thus, it is clear the contribution of these compounds in the hardening in cohesive soils. With regard to the effects of wetting and drying cycles assessed characteristics of the soil (RP and density), it was observed that in general, increasing the number of cycles caused a subtle increase in bulk density. Soils that have gone by 9 cycles of wetting and drying showed a remarkable increase in RP in relation to soils soils that have undergone 3and 6 cycles.
Os Tabuleiros Costeiros apresentam solos com carÃter coeso, os quais podem ocasionar impedimento fÃsico à penetraÃÃo das raÃzes e à dinÃmica da Ãgua. No entanto, a gÃnese desses horizontes nÃo està completamente esclarecida. Dessa forma, objetivou-se com o presente trabalho avaliar a influÃncia de compostos amorfos na gÃnese de horizontes com carÃter coeso em solos de diferentes texturas dos Tabuleiros Costeiros do CearÃ, bem como verificar, atravÃs de anÃlises fÃsicas o comportamento desses solos na presenÃa e na ausÃncia desses compostos. Objetivou-se tambÃm, avaliar a influÃncia de ciclos de umedecimento e secagem no adensamento desses solos. Para avaliaÃÃo do efeito dos compostos amorfos na coesÃo dos solos, foram utilizadas amostras de TFSA de horizontes com carÃter coeso de 9 perfis de solo do estado do CearÃ, sendo estas, submetidas a 2 tratamentos: com e sem extraÃÃo de compostos amorfos. As amostras (com e sem extraÃÃo) foram submetidas a 3 ciclos de umedecimento e secagem e, posteriormente, a resistÃncia à penetraÃÃo (RP), condutividade hidrÃulica e densidade do solo foram determinadas. Para avaliaÃÃo da influÃncia dos ciclos de umedecimento e secagem no adensamento desses solos, foram aplicados 3 diferentes nÃmeros de ciclos de umedecimento e secagem (3, 6, 9 ciclos). ApÃs esses ciclos, a resistÃncia do solo à penetraÃÃo e densidade foram avaliadas. Os acrÃscimos de sÃlica e de alumÃnio de baixa cristalinidade (amorfos) nos horizontes coesos evidenciam que esses compostos contribuem conjuntamente na gÃnese destes horizontes. Independente da textura, os solos que passaram pelo processo de extraÃÃo de compostos amorfos apresentaram uma reduÃÃo significativa na resistÃncia do solo à penetraÃÃo e na densidade. Verificou-se que nesses solos, a condutividade hidrÃulica foi superior Ãquela observada nos solos sem a extraÃÃo dos compostos amorfos. Desse modo, fica clara a contribuiÃÃo desses compostos no endurecimento dos solos coesos. No que se refere aos efeitos dos ciclos de umedecimento e secagem nas caracterÃsticas avaliadas do solo (RP e densidade), observou-se que de um modo geral, o aumento do nÃmero de ciclos provocou um sutil aumento na densidade do solo. Os solos que passaram pelos 9 ciclos de umedecimento e secagem apresentaram um aumento significativo na RP em relaÃÃo aos solos que solos que passaram por 3 e 6 ciclos.

Le sol est un compartiment majeur de stockage du carbone (C) organique de l’écosystème terrestre. Il joue un rôle important dans la régulation du climat. Toute variation des flux de carbone entre l’atmosphère et l’écosystème terrestre pourrait avoir un impact important sur l’augmentation de CO2 dans l’atmosphère, mais aussi sur la diminution des teneurs en matière organique du sol et donc sur la fertilité des sols. Au Nord Cameroun, les sols sont exposés à de longues périodes sèches (5 à 6 mois par an) qui alternent avec une saison humide. La période de transition entre ces deux saisons, peut durer de mi-avril à fin juin et est caractérisée par des pluies très irrégulières. Ces cycles d’humectation-dessiccation pourraient selon la littérature accentuer la minéralisation du carbone organique du sol et le cycle des éléments nutritifs. L’objectif de cette étude est de quantifier l’impact des cycles humectation-dessiccation sur la minéralisation du carbone dans un contexte soudano-sahélien. Pour faire des mesures représentatives sur le terrain, il est nécessaire d’étudier la variation sur 24 heures de la respiration du sol après humectation suite à une période sèche. Cette mise au point méthodologique a montré que la respiration du sol présente une courbe quadratique au cours de la journée, devenant presque linéaire au cours de la nuit. La température et l’humidité du sol ont permis d’expliquer au moins 73% des variations sur 24 heures. Ces observations ont été utilisées pour proposer une méthode pour estimer la respiration moyenne diurne et nocturne après humectation des sols. La méthode proposée dans cette étude a l’avantage d’être basée sur un nombre réduit de mesures et est par conséquent plus facile à mettre en œuvre pour suivre la respiration du sol sur 24 heures après les premières pluies. Une première étude expérimentale de terrain a permis de montrer que la ré-humectation des sols et le mode de gestion des pailles ont augmenté la minéralisation du carbone de ces sols. En revanche, la fréquence des cycles humectation-dessiccation des sols sur une période de 50 jours n’a pas augmenté la minéralisation cumulée du carbone des sols. Au Nord Cameroun, la minéralisation rapide des pailles rend difficile l’augmentation des stocks de carbone du sol par conservation des pailles des cultures précédentes à la surface du sol. Dans une seconde expérimentation de laboratoire, en conditions contrôlées, les cycles humectation-dessiccation n’ont pas augmenté la minéralisation du carbone organique du sol et de l’azote (N) par rapport aux sols maintenus humides. Cependant, les émissions de CO2 ont augmenté avec l’addition de paille enrichie en carbone-13. Cette addition de la paille marquée a augmenté la minéralisation de la matière organique du sol (priming effect). La minéralisation de la paille a diminué avec les cycles humectation-dessiccation et la quantité de paille restante était de 102 µg Cg-1 sol sur les sols ré-humectés contre 48 µg Cg-1 sol sur les sols maintenus humides. L’absence de cette réponse de la minéralisation du carbone et d’azote du sol aux cycles humectation-dessiccation pourrait être liée à une baisse de l’activité microbienne durant les périodes de dessèchement et l’absence d’une augmentation soutenue des taux de minéralisation du carbone avec les cycles ultérieurs d’humectation-dessiccation
Soil as a major storage component for terrestrial ecosystem’s organic carbon plays an important role in regulating climate and agricultural production. Any variation of carbon fluxes between the atmosphere and the terrestrial ecosystem can have a significant impact on the increase of carbon dioxide in the atmosphere but also the decrease in soil organic matter and thus accelarate soil fertility degradation. In northern Cameroon, the transition period between long dry periods with a wet season is characterized by very irregular rainfall that can last several weeks. These wetting-drying cycles can accentuate the mineralization of soil organic carbon and nutrient cycling. The objective of this study is to assess the impact of wet-dry cycles on carbon mineralization in a sudano-sahelian context. From methodological stand field measurements require to study the soil respiration variation over 24 hours after a wet period. This methodological test has shown that soil respiration has a quadratic curve during the day, becoming almost linear during the night. The temperature and soil moisture have explained together the variation over 24 hours (at least 73% ; p< 0.001). These observations have been used to propose a method for estimating the mean daytime and nighttime soil respiration after wetting the soil. Indeed the method proposed in this study has the advantage of being based on a small number of measurements and is, therefore, easier to implement to monitor 24-h soil respiration after the first rains following a long dry period. A first experiment has shown that the wetting of the soil and mulching increased soil carbon mineralization. However, wetting-drying cycles on soil did not increase the cumulative mineralization of soil carbon more than keeping the soil continuously moist. Indeed, in northern Cameroon, the rapid mineralization of crop residues makes it difficult to increase soil carbon stocks by mulching. In a second laboratory experiment, the wetting-drying cycles did not increase organic carbon and nitrogen mineralization from soils added with straw. However, carbon dioxide emissions increased on straw amended soils compared to soils without straw. This addition of the labeled straw increased mineralization of soil organic matter (priming effect). The mineralization of the straw also decreased with the wetting-drying cycles, thus the amount of straw remaining on soils was 102 µg C g-1 soil on re-wetted soils compared to 48 µg C g-1 soil for those with constant moisture. The lack of response for C and N mineralization during wetting-drying cycles may be linked to a decrease of microbial activity during dry periods and the lack of a steady increase in the carbon mineralization rate with subsequent wetting-drying cycles

La durabilité des structures en béton armé ainsi que leur durée de vie sont étroitement liées à la mise en œuvre simultanée de nombreux phénomènes physiques et chimiques. Ceux-ci sont de diverses natures mais restent, en général, fonction des propriétés hydriques des matériaux étudiés. Ainsi, la prédiction des dégradations potentielles d'un matériau cimentaire requiert l'étude du transport de l'eau liquide et des phases gazeuses à travers ce dernier, considéré comme un milieu poreux. En milieu naturel, les structures subissent des variations périodiques de l'humidité relative extérieure (HR). Cependant, la plupart des modèles de transfert hydrique préexistants dans la littérature, s'intéresse uniquement au processus de séchage. Il existe peu de modèles décrivant à la fois l'humidification et le séchage du matériau (ces deux phénomènes se produisent dans le matériau en condition naturelle d'humidité relative (HR)). Tenir compte des phénomènes d'hystérésis dans les transferts hydriques réduit à nouveau le nombre de modèles à disposition. Ainsi, cette thèse s'attache à proposer une meilleure compréhension de l'état hydrique du béton en fonction des variations d'humidité relative extérieure, sur la base d'une nouvelle campagne expérimentale et de modélisations numériques. Un soin sera apporté afin de tenir compte dans les modèles numériques des effets d'hystérésis. Dans ce travail, nous détaillerons, tout d'abord, un modèle multi-phasiques complet. Un modèle simplifié est obtenu, sur la base de considérations théoriques et de vérifications expérimentales dans le cas où la perméabilité intrinsèque à l'eau liquide reste très inférieure à la perméabilité intrinsèque au gaz. Une étude comparative des modèles d'hystérésis couramment utilisés permet d'obtenir un jeu de modèles proposant les meilleures prédictions d'isothermes de sorption d'eau et de leurs hystérésis. Par la suite, le modèle de transport simplifié est couplé avec les modèles d'hystérésis sélectionnés afin de simuler les transferts hydriques dans des bétons soumis à des cycles d'humidification-séchage. La comparaison avec des données expérimentales révèle que la prise en compte de l'hystérésis de l'isotherme de sorption d'eau ne peut pas être négligé. De plus, il est montré que les prédictions obtenues avec des modèles d'hystérésis théoriques, sont les plus cohérentes avec les résultats expérimentaux, en particulier, pour des chemins secondaires d'hystérésis. Plusieurs scénarios (conditions environnementales, bétons différents) sont également simulés. Les résultats obtenus pointent à nouveau la nécessité de tenir compte de l'hystérésis lors de la modélisation des transferts hydriques à travers des matériaux cimentaires soumis à des variations d'humidité relative. La définition d'une profondeur pour laquelle le profil hydrique du béton est modifié par les variations périodiques d'humidité relative permet de mieux comprendre comment la modélisation de la pénétration des espèces ioniques est influencée par les cycles d'humidification-séchage. Par ailleurs, notre analyse révèle qu'il est pertinent de considérer l'effet de Knudsen pour la diffusion de la vapeur afin d'améliorer la prédiction de la diffusivité apparente
The durability of reinforced concrete structures and their service life are closely related to the simultaneous occurrence of many physical and chemical phenomena. These phenomena are diverse in nature, but in common they are dependent on the moisture properties of the material. Therefore, the prediction of the potential degradation of cementitious materials requires the study of the movement of liquid-water and gas-phase transport in the material which is considered as a porous medium. In natural environment, structures are always affected by periodic variations of external relative humidity (RH). However, most moisture transport models in the literature only focus on the drying process. There are few researches considering both drying and wetting, although these conditions represent natural RH variations. Even few studies take into account hysteresis in moisture transport. Thus, this work is devoted to better understand how the moisture behaviour within cementitious materials responds to the ambient RH changes through both experimental investigations and numerical modelling. In particular, hysteretic effects will be included in numerical modelling. In this thesis, we first recalled a complicate multi-phase continuum model. By theoretical analysis and experimental verification, a simplified model can be obtained for the case of that the intrinsic permeability to liquid-water is smaller than the intrinsic permeability to gas-phase. The review of commonly-used hysteresis models enabled to conclude a set of best models for the prediction of water vapour sorption isotherms and their hysteresis. After that, the simplified model was coupled with selected hysteresis models to simulate moisture transport under drying and wetting cycles. Compared with experimental data, numerical simulations revealed that modelling with hysteretic effects can provide much better results than non-hysteresis modelling. Among different hysteresis models, results showed that the use of the conceptual hysteresis model, which presents closed form scanning loops, can provide more accuracy predictions. Further simulations for different scenarios were also performed. All comparisons and investigations enhanced the necessity of considering hysteresis to model moisture transport for varying relative humidity at the boundary. The investigation of moisture penetration depth could provide a better understanding of how deep moisture as well as ions can move into the material. Furthermore, the analysis revealed that the consideration of Knudsen effects for diffusion of vapour can improve the prediction of the apparent diffusivity

A resiliência física de solos é proveniente de processos regenerativos que incluem ciclos de umedecimento e secamento, congelamento e descongelamento assim como as atividades biológicas. Este estudo testou a hipótese de que as propriedades físicas do solo,tais como a permeabilidade do solo ao ar, densidade do solo, porosidade de aeração e porosidade total são indicadores físicos eficientes para quantificar a resiliência de solos de diferentes texturas submetidos ao estresse mecânico (compactação) e após subseqüentes ciclos de umedecimento e secamento. O objetivo foi avaliar o comportamento e a resiliência do solo por meio de propriedades físicas de um Latossolo Vermelho. Foram retiradas 25 amostras indeformadas (0-0,05m) de dois solos: solo I com textura argilosa e solo II com textura franco argilo arenosa, realizando as determinações das propriedades físicas nos tratamentos: antes da compactação(A), depois da compactação (C0) e após ciclos de umedecimento e secamento (C1,C2,C3,C4). As propriedades densidade do solo e porosidade total não apresentaram recuperação da condição inicial após a compactação nos solos I e II, as propriedades conteúdo volumétrico de água e porosidade de aeração apresentaram recuperação parcial apenas no solo I, para o solo II também não apresentaram recuperação, e a permeabilidade do solo ao ar foi a propriedade que apresentou a melhor recuperação assim como foi a que apresentou maior resiliência. Em relação ao distinto comportamento dos dois solos, observou-se que o solo I foi mais resiliente que o solo II nas propriedades que apresentaram recuperação.
The soil physical resilience comes from regenerative processes which include cycles of wetting and drying, freezing and thawing as well as biological activities. This study tested the hypothesis that the physical properties of soil such as soil permeability, bulk density, aeration porosity and total porosity are efficient physical indicators to quantify the resilience of soils of different textures subjected to mechanical stress (compression) and after subsequent cycles of wetting and drying. The objective was to evaluate the behavior and soil resilience by means of physical properties of an Oxisol. Undisturbed samples were taken 25 (0-0.05 m) of two soils: clayey soil and soil with sandy clay loam texture, making determinations of physical properties in the treatments before compression (A), after compaction (C0) and after wetting and drying cycles (C1, C2, C3, C4). The bulk density properties and porosity did not recover the initial condition after compression in the soil I and II, the properties volumetric content of water and air-filled porosity showed only partial recovery in the soil I, II to the soil also showed no recovery and soil permeability to air was the property that showed the best recovery as well as showed the greatest resilience. Regarding the different behavior of the two soil, it was observed that the soil I was more resilient soil II in which showed recovery properties

The cyclic wetting and drying of a rock is considered to be one of a number of physical weathering processes that have an effect on the weathering of rock. While the presence of moisture is known to be of critical importance for the activation and enhancement of a number of other known weathering processes, such as cryogenic weathering, salt weathering and slaking it is possible that the mere cyclic application and removal of moisture over time may also have an effect on the physical structure of a rock. The precise nature of the process is not well understood, however. This document begins by investigating the studies that have previously been undertaken to determine how the wetting and drying weathering process is defined and to ascertain the current state of knowledge regarding this process. After an establishment of background context, a physical experiment is carried out on Clarens Formation sandstone and Marion Island basalt to note the relationship between cyclic wetting and drying and the changing physical properties of the rocks. The rocks were subjected to 105 wetting and drying cycles over a period of 21 weeks. At the beginning of the experiment, physical rock properties were measured by way of the method laid out by Cooke (1979) and again at the end of the experiment. Since the experiment was carried out under static environmental conditions, the comparison of physical rock properties gives a good indication of how the rocks have altered their structure over the experimental time period. The results obtained in this experiment show that different rock types will change in different ways when exposed to a common weathering process. The basalt samples experienced no mass loss at, while the sandstones did. The sandstones, which are rocks that are of common lithology and of very similar physical and chemical structure reacted to the wetting and drying weathering process in ways that could not be predicted without experimentation. The data does show a clear causal link between the application of external stimuli and rock property change, however. Changes in physical rock properties are not always straightforward and linear, but evolve dynamically over time, often yielding results that appear to oppose those intuitively predicted. A number of questions are asked regarding the philosophical approach that is taken to process isolation studies, with emphasis given to the careful consideration of the place that such studies have in the realm of process geomorphology. While process isolation studies may give an excellent indication of what a particular weathering process may be capable of under certain conditions and on certain rock types, they should not be regarded as indicative of what is occurring in the field. Additionally, it has become clear that it is not possible to predict how a specific rock type may respond to a specific weathering process without physical experimentation since the number of variables present in a typical weathering system are simply too vast to easily categorise.
Dissertation (MSc)--University of Pretoria, 2010.
Geography, Geoinformatics and Meteorology
MSc
Unrestricted

Preventing chloride-induced reinforcement corrosion in marine concrete structures remains a concern for structural engineers. Marine structures are typically exposed to high chloride concentrations through direct exposure to sea water, which provides the primary conditions required for reinforcement corrosion. The progress of corrosion can be controlled through anodic, cathodic or resistivity processes. However, high chloride concentrations tend to prevent anodic control from governing the corrosion rate, while direct exposure to moisture generally prevents resistivity control. Consequently, cathodic control remains an important process in the marine environment to restrict the progress of corrosion. The primary cathodic reaction in reinforcement corrosion is the reduction of oxygen, and as a result the availability of oxygen is a key factor when considering reinforcement corrosion in the marine tidal zone. The corrosion rate may be effectively reduced if the drying time of the concrete during tidal cycles is sufficiently short, thereby reducing the oxygen supply at the level of the embedded steel.

Long linear earthwork assets constructed in high-plasticity overconsolidated clay are known to be deteriorating due to long-term effects of wetting and drying stress cycles as a result of seasonal weather patterns. These stress cycles can lead to shallow first-time failures due to the mobilisation of post-peak strength and progressive failure. Design requirements of new earthworks and management of existing assets requires improved understanding of this critical mechanism; seasonal ratcheting. Incremental model development and validation to allow investigation of multiple inter-related strength deterioration mechanisms of cut slope behaviour in high-plasticity overconsolidated clay slopes has been presented. Initially, the mechanism of seasonal ratcheting has been considered independently and a numerical modelling approach considering unsaturated behaviour has been validated against physical modelling data. Using the validated model, the effects of slope geometry, design parameter selection and design life have been considered. Following this, an approach to allow undrained unloading of soil, stress relief, excess pore water pressure dissipation, seasonal ratcheting and progressive failure with wetting and drying boundary conditions has been considered. Hydrogeological property deterioration and the potential implications of climate change have been explored using the model. In both cases the serviceable life of cut slopes is shown to reduce significantly in the numerical analyses. Finally, a model capable of capturing hydrogeological behaviour of a real cut slope in London Clay has been developed and validated against long-term field monitored data. Using the validated model, a climate change impact assessment for the case study slope has been performed. The numerical analyses performed have indicated that seasonal ratcheting can explain shallow first-time failures in high-plasticity overconsolidated clay slopes and that the rate of deterioration of such assets will accelerate if current climate change projections are representative of future weather.

Expansive soils are a worldwide problem especially in the regions where climate is arid or semi arid. These soils swell when they are exposed to water and shrink when they dry. Cyclic swelling and shrinkage of clays and associated movements of foundations may result in cracking of structures. Several methods are used to decrease or prevent the swelling potential of such soils like prewetting, surcharge loading, chemical stabilization etc. Among these, one of the most widely used method is using chemical admixtures (chemical stabilization). Cyclic wetting and drying affects the swell &ndash
shrink behaviour of expansive soils. In this research, the effect of cyclic swell &ndash
shrink on swell percentage of a chemically stabilized expansive soil is investigated. Class C Fly Ash is used as an additive for stabilization of an expansive soil that is prepared in the laboratory environment by mixing kaolinite and bentonite. Fly ash was added to expansive soil with a predetermined percentage changing between 0 to 20 percent. Hydrated lime with percentages changing between 0 to 5 percent and sand with 5 percent were also used instead of fly ash for comparison. Firstly, consistency limits, grain size distributions and swell percentages of mixtures were determined. Then to see the effect of cyclic swell &ndash
shrink on the swelling behavior of the mixtures, swell &ndash
shrink cycles applied to samples and swell percentages were determined. Swell percentage decreased as the proportion of the fly ash increased. Cyclic swell-shrink affected the swell percentage of fly ash stabilized samples positively.

碩士
國立臺灣大學
土木工程學研究所
105
Taiwan is located in the subtropical and surrounded by the sea. Due to the invasion of salt, it may lead to corrosion of steel in the coastal structures. As a result, understanding the mechanism of chloride intrusion into the concrete for the durability of concrete design and thickness of the protective layer is important. Coastal structures situated in the tidal zone and splash zone have been identified as being the most susceptible to salt erosion. Considering the practical marine engineering, it often uses low water-cement ratio of concrete to design structures. This study selected concrete with a water-cement ratio of 0.45 and with the addition of different pozzolan materials to explore the transmission behavior of chloride ions in salt ponding test(P group) and drying-wetting cycle test(C2 and C3 groups). Finally, using the evaluation index of "chloride ion invasion depth", "chloride ion diffusion coefficient" and "total amount of chloride ion invasion" to judge the difference of chloride ion invasion. The main transport mechanism of chloride ion under salt ponding test is diffusion. Generally, it can use the diffusion equation to describe the distribution of chloride ions in concrete. As for the drying-wetting cycle test, The invasion of chloride ions is mainly due to the contribution of capillary adsorption and diffusion. Some scholars use the modified diffusion equation taking into account the convection zone to describe the transmission of chloride ion under drying-wetting cycle test. In order to compare the difference between the salt ponding test and the drying-wetting cycle test on the invasion depth of chloride ions, the regression analysis was carried out for the experimental values of the convection zone in the literature. By using the diffusion equation with the modified diffusion equation, we can establish the model of the chloride ion invasion for both salt ponding test and drying-wetting cycle test. It can be seen that the experimental data from the four test ages is highly fitted with the invasive depth model. In other words, it shows good predictability in this invasive depth model. In addition, the experimental results show that in the six mixes, 045S40 and 045S50 perform well in some index of evaluation such as "depth of chloride ion invasion", "chloride ion diffusion coefficient" and "total amount of chloride ion".

No
There is an increasing interest in the use of Ground Source Heat Pumps (GSHPs) as a source of renewable energy in temperate countries. GSHPs coupled with buried heat collectors can harness the thermal energy from near-surface soils to provide the heating required for domestic properties. The performance of a GSHP system depends greatly on the thermal conductivity of the surrounding soils. Near-surface soils undergo cycles of drying and wetting due to, for example, the infiltration of rain water and/or fluctuations of the ground water table. Several parameters - including the properties of soil, suction head and saturation history - affect the thermal properties as well as the retention and flow of water. This paper presents results from a comprehensive laboratory investigation on sand samples with markedly different grain size distribution. Simultaneous measurements of thermal and hydraulic properties of the sands were taken under incremental increase/decrease in the suction head values to simulate cycles of drying and wetting. The results clearly suggest that the thermal conductivity is better expressed as a function of the matric suction head so as to reflect the saturation history. There has been almost five-fold increase in the measured value of thermal conductivity when the soil was wetted to a residual degree of saturation from being dry.

碩士
國立臺灣大學
土木工程學研究所
106
Taiwan is located in the subtropical, surrounded by the sea and the weather is not only humid but also high tempature. Due to the invasion of salt, it could casue corrosion of steel in coastal concrete structures. Normally, most of the people believe corrosion of steel under the sea is most severe, in fact many researches shows that area situated in the tidal zone and splash zone where having drying-wetting cycle effect has the most severe corrosion of steel. Therefore, it should conduct the durability of concrete design and the selection of thickness of protective layer. The main transport behavior of chloride ion under salt ponding test is diffusion. As for the drying-wetting cycle test, the transport behavior of chloride ions is mainly due to the contribution of capillary adsorption and diffusion. Thus, under the effect of drying-wetting cycle, chloride ions surface layer has accumulation of concentration and casue convection zone. Researches indicate after the produce of convection zone, both the invasion depth of chloride ions and total amount of chloride ion increase. In order to carry out the evaluation of concrete durability, “chloride ion diffusion coefficient”, “convection zone depth”, “chloride ion invasion depth” and “total amount of chloride ion invasion” these indexes are being used. In order to compare different convection zone depth influences on chloride ion invasion behavior, designing three types of water-colloid ratio (0.45, 0.55, 0.65), two types of pozzolan material replacement (OPC, SF50) and three types of drying-wetting cycle mechanism (ponding test, cycle of 14 days, cycle of 28 days). To dicuss above variables effect on convection zone depth. This study used water-soluble chloride ion titration to get chloride ion concentration for each depth and convection zone depth, the regression analysis was carried out for the literatures collected, and then get the regression equation of convection zone depth. By using the regression equation with the modified diffusion equation, we can establish model of the chloride ion invasion depth for drying-wetting test and verify the model by the chloride ion depth produced from colorimetric method. According to the test result, the chloride ion invasion depth of drying-wetting cycle test is equal to the chloride ion invasion depth of ponding test plus convection zone depth. The longer the period of drying-wetting cycle, the deeper the convection zone depth. As for the regression equation of convection zone depth and model of invasion depth, the literature and test results of this study indicate that they are highly fitted, therefore it has high level of reference value.

abstract: In a laboratory setting, the soil volume change behavior is best represented by using various testing standards on undisturbed or remolded samples. Whenever possible, it is most precise to use undisturbed samples to assess the volume change behavior but in the absence of undisturbed specimens, remodeled samples can be used. If that is the case, the soil is compacted to in-situ density and water content (or matric suction), which should best represent the expansive profile in question. It is standard practice to subject the specimen to a wetting process at a particular net normal stress. Even though currently accepted laboratory testing standard procedures provide insight on how the profile conditions changes with time, these procedures do not assess the long term effects on the soil due to climatic changes. In this experimental study, an assessment and quantification of the effect of multiple wetting/drying cycles on the volume change behavior of two different naturally occurring soils was performed. The changes in wetting and drying cycles were extreme when comparing the swings in matric suction. During the drying cycle, the expansive soil was subjected to extreme conditions, which decreased the moisture content less than the shrinkage limit. Nevertheless, both soils were remolded at five different compacted conditions and loaded to five different net normal stresses. Each sample was subjected to six wetting and drying cycles. During the assessment, it was evident from the results that the swell/collapse strain is highly non-linear at low stress levels. The strain-net normal stress relationship cannot be defined by one single function without transforming the data. Therefore, the dataset needs to be fitted to a bi-modal logarithmic function or to a logarithmic transformation of net normal stress in order to use a third order polynomial fit. It was also determined that the moisture content changes with time are best fit by non-linear functions. For the drying cycle, the radial strain was determined to have a constant rate of change with respect to the axial strain. However, for the wetting cycle, there was not enough radial strain data to develop correlations and therefore, an assumption was made based on 55 different test measurements/observations, for the wetting cycles. In general, it was observed that after each subsequent cycle, higher swelling was exhibited for lower net normal stress values; while higher collapse potential was observed for higher net normal stress values, once the net normal stress was less than/greater than a threshold net normal stress value. Furthermore, the swelling pressure underwent a reduction in all cases. Particularly, the Anthem soil exhibited a reduction in swelling pressure by at least 20 percent after the first wetting/drying cycle; while Colorado soil exhibited a reduction of 50 percent. After about the fourth cycle, the swelling pressure seemed to stabilized to an equilibrium value at which a reduction of 46 percent was observed for the Anthem soil and 68 percent reduction for the Colorado soil. The impact of the initial compacted conditions on heave characteristics was studied. Results indicated that materials compacted at higher densities exhibited greater swell potential. When comparing specimens compacted at the same density but at different moisture content (matric suction), it was observed that specimens compacted at higher suction would exhibit higher swelling potential, when subjected to the same net normal stress. The least amount of swelling strain was observed on specimens compacted at the lowest dry density and the lowest matric suction (higher water content). The results from the laboratory testing were used to develop ultimate heave profiles for both soils. This analysis showed that even though the swell pressure for each soil decreased with cycles, the amount of heave would increase or decrease depending upon the initial compaction condition. When the specimen was compacted at 110% of optimum moisture content and 90% of maximum dry density, it resulted in an ultimate heave reduction of 92 percent for Anthem and 685 percent for Colorado soil. On the other hand, when the soils were compacted at 90% optimum moisture content and 100% of the maximum dry density, Anthem specimens heave 78% more and Colorado specimens heave was reduced by 69%. Based on the results obtained, it is evident that the current methods to estimate heave and swelling pressure do not consider the effect of wetting/drying cycles; and seem to fail capturing the free swell potential of the soil. Recommendations for improvement current methods of practice are provided.
Dissertation/Thesis
Ph.D. Civil and Environmental Engineering 2013

碩士
國立高雄應用科技大學
土木工程與防災科技研究所
98
Pozzolanic concrete has been widely used in various projects. In this study, fly ash and slag concretes were placed in the solution of 5 % sodium sulfate under drying-wetting and temperature change cycles and long-term immersion, to simulate the effect of structures in tidal zones and seawater. The durability of concrete is assessing by using modified Accelerated Chloride Migration Test (ACMT). The results indicate that adding 20 % fly ash and 40 % slag concrete curing at 23 ° C and 100 % R.H. for 3 months, the chloride ion non-steady state migration coefficient (Mn) were 69 % and 28 % that of ordinary concrete, separately. Ordinary and fly ash concrete were placed in the solution of 5 % sodium sulfate under drying-wetting and temperature change cycles for 12 weeks, Mn were reduced to 82% and 33% of the initial value, separately. This result represented the ability of resisting chloride ion penetration continually increased. However, Mn of slag concrete became 2 times of the initial value, it represented that slag concrete was deteriorated under drying-wetting and temperature change cycles. In addition, we found that Mn was approximately 3 – 10 times against steady state migration coefficient (Ms), and it’s higher than the predicted value of the NIST program. This result indicating the modified ACMT will underestimate the durability of concrete, but it still can be a method for comparing durability of different kinds of concrete.

Research Doctorate - Doctor of Philosophy (PhD)
This Thesis presents the results of a comprehensive experimental research aimed at studying the influence of environmental effects, as those caused by cyclic variations in relative humidity (RH) and temperature, on the behaviour of Ashfield shale, a low porosity clayey rock from the Sydney Basin. The experimental program focused on tracking the progressive degradation of engineering properties such as rock stiffness, rock permeability, rock compressibility, rock shear strength and rock tensile strength. Five main aspects were evaluated in this research: (i) the influence of the number of RH cycles, N, (ii) the influence of the amplitude of the RH cycle, ∆RH, (iii) the effects of the stress level, (iv) the effects of low-temperature changes caused by freezing/thawing cycles and (v) the effects of using either liquid water or water vapour during wetting paths on rock degradation. A new high-pressure isotropic apparatus was designed and constructed in this research to induce and track hydraulic degradation of clayey rocks under controlled laboratory conditions. In addition, non-conventional experimental techniques such as bender elements transducers as well as gas pulse tests were implemented in this research to monitor variations in rock stiffness and rock permeability. Consequences of the aforementioned environmental effects on rock microstructure were studied via Mercury Intrusion Porosimetry (MIP) tests as well as Scanning Electron Microscopy with Energy Dispersive Spectrometer (SEM-EDS) analysis. The experimental results showed that the exposure of Ashfield shale to environmental factors such as relative humidity cycling (either via vapour or liquid transfer), freezing-thawing cycles (at saturated and unsaturated conditions) and changes in the confining state, led to a progressive degradation of its hydro-mechanical properties. The interaction of the rock with liquid transfer caused larger degradation compared to tests in which saturation was achieved via vapour transfer. The application of low temperature cycles (freezing/thawing) proved to be the most harmful degradation factor. Rock degradation is strongly influenced by the stress level. Degradation of the shear strength reduced with increasing the vertical stress at which RH cycles were applied. Stress relief after the exposure of RH cycles was also observed to play an important role on the degradation of the shear strength in Ashfield shale. A remarkable reduction in rock shear strength, rock tensile strength, rock stiffness as well as an important increase in rock compressibility and rock permeability was clearly observed in the laboratory tests carried out in this research. This was accompanied by a progressive accumulation of irreversible volumetric strains which seemed to follow the framework of behaviour described by Pineda et al. (2014).

碩士
國立臺灣科技大學
營建工程系
107
A mixture of bentonite and sand is considered as a buffer and backfill materials in the multi-barrier system of the radioactive waste disposal facility, because of their high swelling potential which enables to seal the pores within the materials and low hydraulic conductivity which reduces the possibility of nuclear extravasation by groundwater. During the operation of the disposal facility, the buffer and backfill materials need to overcome the changes of the environment, such as the migration of groundwater level which may transform the materials from saturated condition into unsaturated, and the properties of buffer and backfill materials will be affected. A mixture of bentonite Kunigel-V1RW, produced in Japan, and quartz sand has been used in this study. The specimens were made from bentonite and quartz sand in various proportions. The laboratory tests including swelling deformation, swelling pressure, and hydraulic conductivity were performed. The influence of drying-wetting cycle on the swelling deformation and swelling pressure of specimens were examined. The results showed that the buffer and backfill materials have a marked change on the swelling behavior under the action of drying and wetting cycle. The ratio of change of swelling performance after wetting will decrease linearly with the increment of water content at the end of the drying stage. In addition, when the ratio of change of swelling performance is zero, the corresponding water content is close to the shrinkage limit. The reason causing these results was surmised that the process of drying and wetting leads to the destruction and the reconstruction of the particle structure. When the drying water content of the specimen is higher than the shrinkage limit, the arrangement of particle tends to dispersed structure and makes the re-wetting swelling performance decrease, on the other hand, when the drying water content of the specimen is lower than the shrinkage limit, the arrangement of particle tends to flocculated structure with less orientation and makes the re-wetting swelling performance increase.