Dissertations / Theses on the topic 'Sand retention'

Avec les récents développements des mesures de champs, il est devenu possible deréaliser des expériences sur un échantillon de sol en effectuant des mesures simultanémentaux différentes échelles pertinentes : celle de l'échantillon, et celle des grains, et ceci en3D volumique. Ces progrès ont permis une meilleure compréhension des processus qui seproduisent dans le sol, en les observant au cœur même des échantillons.Cette thèse vise à caractériser les comportements de rétention d'eau et hydro-mécaniquedu sable d'Hostun non saturé à l'échelle du grain. Pour ce faire, des essais de rétentiond'eau et des essais triaxiaux ont été effectués, qui ont nécessité le développement d'outils detraitement d'image et des montages expérimentaux spécifiques. L'installation de tomographie à rayons X du Laboratoire 3SR de l'Université des Grenoble a été utilisée pour générer des images en 3D de la microstructure du sol non saturé. Une technique de trinarization a été mise en œuvre pour permettre la séparation des phases (les grains, l'eau et l'air) dans les images 3D, et d'effectuer différentes mesures à l'échelle du grain. La porosité et le degré de saturation ont été mesurées macroscopiquement en utilisant les images segmentées, et microscopiquement en utilisant un code de cartographie spécialement développé. Les mesures microscopiques ont été réalisées sur un volume élémentaire représentatif (VER), dont la taille a été déterminée en utilisant une analyse développée sur la base d'outils statistiques. Plusieurs analyses discrets ont été développées pour étudier l'évolution de la phase fluide (l'eau et l'air) avec le chargement (succion, et chargement mécanique). La corrélation d'images numérique 3D volumique a été mise en œuvre systématiquement pour ces deux types d'essais.Pour analyser le comportement de rétention d'eau du sable d'Hostun pendant les processus de séchage et de mouillage, une cellule spécifique a été développée. La succion a été appliquée en utilisant la technique de tensiomètre. L'échantillon (cylindrique 1x1cm) a été préparé en utilisant la technique de la pluviation sous l'eau et scanné avec une résolution de 7,5micron. La courbe de rétention d'eau, surface et les domaines hydriques ont été obtenus et le phénomène d'hystérésis et la cohésion du sol ont été analysés à l'échelle du grain.Pour le comportement hydro-mécanique des sols non saturés, des essais triaxiaux ontété effectué sous trois conditions: saturé drainé, non saturé drainé et non saturé non drainé. Un appareil triaxial que l'on peut placer à l'intérieur de la cabine du tomographe à rayons X a été développé afin de permettre le suivi des changements dans la microstructure du sable et la distribution de l'eau lorsque l'on soumet l'échantillon à chargement mécanique. L'échantillon (cylindre de dimensions hxd=2x1cm) a été préparé en utilisant la technique de la pluviation sous l'eau (complétement saturé au début des trois tests), amené ensuite au niveau de saturation désiré (dans le cas des essais non saturés), puis chargé par étapes successives avec scan à chaque étape avec une résolution de 13micron, jusqu'à arriver à 21% de déformation axiale pour les trois types d'essai. Les courbes contrainte-déformation, la réponse volumétrique et les déformations ont été obtenus et le profil de déformation, l'hétérogénéité de l'échantillon, la cohésion et la distribution de l'eau ont été analysés
With the recent developments of full field measurements, it has become possible to do experiments on a soil specimen, and perform measurements at different scales. This progress has allowed greater understanding for all the processes that occur within the soil, and also created better environment to observe these mechanisms in 3D. This PhD work aims to characterize water retention and hydro-mechanical behaviours of unsaturated Hostun sand at the grain scale. To achieve this goal, water retention and triaxial tests were performed and a set of experimental and image processing tools was developed and used for the two series of tests. X-ray computed tomography set up available at 3SR Laboratory in Grenoble University was used to generate 3D images of the unsaturated soil microstructure non-destructively. A developed region growing systematic technique (trinarization technique) was used to allow the separation of the phases (i.e., grains, water and air) in the 3D images, and performing different measurements at the grain scale. Porosity and degree of saturationwere measured macroscopically using the trinarized images and microscopically using a developed mapping code. The microscopic measurements were performed over an REV, whose size was determined using a developed analysis based on statistical tools. Several microscopic-discrete analyses were developed to investigate the evolution of fluid phase (water and air) with loading (suction and mechanical loading). Digital Image Correlation was performed for the two tests.To analyze water retention behaviour of Hostun sand during drying and wetting processes, a pressure plate apparatus was developed. Suction was applied using tensiometry technique. The specimen (cylindrical 1x1cm) was prepared using water pluviation technique and scanned with a resolution 7.5micron. As a result, water retention curve, surface and domains were obtained and hysteresis phenomenon and soil cohesion were analyzed at the grain scale.For the mechanical behaviour of unsaturated soils, triaxial test were performed at three conditions: saturated drained, unsaturated drained and unsaturated undrained. A triaxial apparatus that can be placed inside the x-ray cabinet was developed in order to facilitate monitoring the changes in sand microstructure and water distribution when subjecting the soil specimen to loading. The specimen (cylinder of hxd=2x1cm) was prepared using water pluviation technique (completely saturated at the beginning of the three tests), loaded then scanned with a resolution 13micron, repeatedly till reaching 21% axial strain forthe three tests.Consequently, stress-strain curves, volumetric response and deformations measurements were obtained and deformation pattern, specimen heterogeneity, cohesion and water distribution were analyzed

Constructed wetlands are considered an inefficient technology for long-term phosphorus (P) removal. The P retention effectiveness of subsurface wetlands can be improved by using appropriate substrates. The objectives of this study were to: (i) use sorption isotherms to estimate the P sorption capacity of the two materials, masonry sand and light weight expanded shale; (ii) describe dissolved P removal in small (2.7 m3) subsurface flow wetlands; (iii) quantify the forms of P retained by the substrates in the pilot cells; and (iv) use resulting data to assess the technical and economic feasibility of the most promising system to remove P. The P sorption capacity of masonry sand and expanded shale, as determined with Langmuir isotherms, was 60 mg/kg and 971 mg/kg respectively. In the pilot cells receiving secondarily treated wastewater, cells containing expanded shale retained a greater proportion of the incoming P (50.8 percent) than cells containing masonry sand (14.5 percent). After a year of operation, samples were analyzed for total P (TP) and total inorganic P (TIP). Subsamples were fractionated into labile-P, Fe+Al-bound P, humic-P, Ca+Mg-bound P, and residual-P. Means and standard deviations of TP retained by the expanded shale and masonry sand were 349 + 169 and 11.9 + 18.6 mg/kg respectively. The largest forms of P retained by the expanded shale pilot cells were Fe+Al- bound P (108 mg/kg), followed by labile-P (46.7 mg/kg) and humic-P (39.8). Increases in the P forms of masonry sand were greatest in labile-P (7.5 mg/kg). The cost of an expanded shale wetland is within the range of costs conventional technologies for P removal. Accurate cost comparisons are dependent upon expansion capacity of the system under consideration. Materials with a high P sorption capacity also have potential for enhancing P removal in other constructed wetland applications such as stormwater wetlands and wetlands for treating agricultural runoff.

In recent years the nutrient levels of the Upper Floridan aquifer have been increasing (USGS, 2008). An example of this is found in Ocala, Florida where Silver Springs nitrate concentrations have risen from 0.5 mg/L in the 1960 s to approximately 1.0 mg/L in 2003 (Phelps, 2004). Because stormwater is a contributor to surficial and groundwater aquifer recharge, there is an increasing need for methods that decrease nitrogen and phosphorus levels. A laboratory column study was conducted to simulate a retention pond with saturated soil conditions. The objectives of the column studies reported in this thesis were to investigate the capabilities of a natural soil and soil augmentations to remove nitrogen and phosphorus for a range of concentrations at three different temperatures. An analytical attempt to model the columns through low order reaction kinetics and derive the corresponding temperature conversion constant to relate the rate constants is also presented. The Media Mixes were selected through a process of research, preliminary batch testing and then implemented in column studies. Three columns measuring three feet in length and 6 inches outer diameter were packed with a control and two media mixes. Media Mix 1 consisted of 50% fine sand, 30% tire crumb, 20% sawdust by weight and Media Mix 2 consisted of 50% fine sand, 25% sawdust, 15% tire crumb, 10% limestone by weight. The control column was packed with natural soil from Hunter s Trace retention pond located in Ocala, Florida. The reaction rates for nitrate are best modeled as first order for Media Mix 1, and zero order for the Control and Media Mix 2. The reaction rates for orthophosphate are best modeled as zero order, second order and first order for the Control, Media Mix 1, and Media Mix 2 respectively. The best overall media for both nitrate and orthophosphate removal from this study would be Media Mix 1. Media Mix 2 does have the highest average orthophosphate removal of all the mixes for all of the temperatures; however Media Mix 1 outperforms Mix 2 for the other two temperatures. The best column for Nitrate removal is the Media Mix 1 column. The temperature conversion factors for nitrate were found to be 1.11, 1.1, and 1.01 for Media Mix 1, the Control and Media Mix 2 respectively. The temperature conversion factors for orthophosphate were found to be 1.02, 0.99, and 0.95. As well as temperature conversion factors, the activation energies and frequency factors for the Arrhenius Equation were investigated. Average values corresponding to each column, species, and temperature would be inaccurate due to the large variation in calculated values.
M.S.
Department of Civil and Environmental Engineering
Engineering and Computer Science
Environmental Engr MSEnvE

[Truncated abstract] Self-filtration is here defined as particle detachment and re-deposition causing re-arrangement of the particles and therefore pore space which affects water flow in soil by decreasing hydraulic conductivity. This is of particular important in soils which are susceptible to structural breakdown. The objective of this thesis was to examine the dynamics of the self-filtration process in sodic sandy soils as affected by ionic strength and soil solution composition. The temporal changes of hydraulic conductivity and the elution of fine particles from soil columns were used as the main criteria to assess selffiltration. Two porous media exhibiting significantly different structural cohesion were examined, one a loamy sand (Balkuling soil) from agricultural land use and the second a mining residue from mineral sands operations . . . The effects of the composition of mixed calcium (Ca) and sodium (Na) ions in solution (sodium adsorption ratio (SAR)) on the exchange behaviour and saturated hydraulic conductivity were examined by carrying out batch binary exchange and saturated column transport experiments. A strong preference for Ca2+ ions in the exchange complex was observed for both soils. Generally K/Ko was found to decrease with increasing sodium adsorption ratio with the more structured Balkuling soil maintaining K/Ko for SARs 3 and 5 at an electrolyte concentration of 100 mmol/L. However measurements at the critical threshold and turbidity concentrations at a SAR of 15 revealed structural breakdown of the pore matrix system attributed to various extents of slaking, swelling, dispersion and decreases of pore radii as a result of selffiltration during leaching. These experiments illustrate the wide range of complex interactions involving clay mineralogy, solution composition and structural factors which can influence the extent of mobilization, transport and re-deposition of colloidal particles during the leaching process in soil profiles.

Laboratory experiments utilizing closed and open system experiments were conducted in this study to evaluate the applicability of using an electro-kinetic process to concentrate and retain nitrate close to the anode. A finite difference model was developed to predict the pH gradient developed during the electro-kinetic process. Model results then were used with a derived regression equation between pH and N0₃- to predict the nitrate gradient developed during an electro-kinetic process. The results of this research revealed that an electro-kinetic method is an effective means for concentrating and retaining nitrate close to the anode in saturated sandy soil even under a strong hydraulic gradient. Results also support the validity of using a finite difference and regression equation model to predict the spatial and temporal distribution of N0₃- developed under an electro- kinetic process for both closed and open system configurations.

This study proposed to explore several factors that promote foster parent satisfaction in order to preserve quality foster homes to serve the 532,000 displaced children currently in the child welfare system. A sample of 52 foster parents were surveyed to determine overall satisfaction with their foster care experience at Children's Way Foster Family Agency in San Bernardino, California. It was hypothesized that the higher the level of foster parent satisfaction, the higher rates of retention. A modified version of an existing instrument titled "Foster Parent Satisfaction Survey" was utilized in this study.

An extensive amount of natural gas trapped in the subsurface is found as methane hydrate. A fundamental understanding of natural hydrate-bearing sediments is required to engineer production strategies and to assess the risks hydrates pose to global climate change and large-scale seafloor destabilization. This thesis reports fundamental studies on hydrate nucleation, morphology and the evolution of unsaturation during dissociation, followed by additional studies on sampling and pressure core testing. Hydrate nucleation is favored on mineral surfaces and it is often triggered by mechanical vibration. Continued hydrate crystal growth within sediments is governed by capillary and skeletal forces; hence, the characteristic particle size d10 and the sediment burial depth determine hydrate morphologies in natural sediments. In aged hydrate-bearing sand, Ostwald ripening leads to patchy hydrate formation; the stiffness approaches to the lower bound at low hydrate saturation and the upper bound at high hydrate saturation. Hydrate saturation and pore habit alter the pore size variability and interconnectivity, and change the water retention curve in hydrate-bearing sediments. The physical properties of hydrate-bearing sediments are determined by the state of stress, porosity, and hydrate saturation. Furthermore, hydrate stability requires sampling, handling, and testing under in situ pressure, temperature, and stress conditions. Therefore, the laboratory characterization of natural hydrate-bearing sediments faces inherent sampling disturbances caused by changes in stress and strain as well as transient pressure and temperature changes that affect hydrate stability. While pressure core technology offers unprecedented opportunities for the study of hydrate-bearing sediments, careful data interpretation must recognize its inherent limitations.

L’utilisation de tensioactifs de type alpha-oléfinésulfonate dans les procédés de récupération améliorée du pétrole apparait comme une solution à des gisements pétroliers possédant une eau de gisement moyennement salée contenant des cations divalents. L’optimisation du procédé passe par l'élaboration d'un modèle de transport traduisant l'évolution de la concentration du tensioactif, donc de son efficacité, lors de son transit au sein du milieu poreux que constitue le gisement. La modélisation s'est appuyée sur une méthode expérimentale reposant sur la chromatographie réactive, qui permet à partir de l'analyse de la réponse d'un milieu poreux à un signal de concentration de déduire qualitativement et quantitativement les interactions qui contrôlent le transport de l'espèce étudiée. Les expériences ont été effectuées sur un sable argilo-calcaire, le sable de gue et sur un mélange artificiel de sable d'argile, imprégné par de l'asphalte. Le mélange de tensioactif utilisé est une alphaoléfinésulfonate de sodium commerciale en C14-C16. Trois phénomènes prépondérants contrôlent le transport de ce tensio-actif au-dessus de la concentration micellaire critique: (1) l'adsorption est essentiellement contrôlée par la concentration en magnésium qui n'est pas contrôlée par les équilibres calcocarboniques (ii) la séparation chromatographique du mélange en trois classes de produits lors de l'adsorption (iii) le partage du à la présence d'asphalte sur la surface qui augmente notablement la capacité de rétention du milieu. À partir de ces observations un modèle global a été développé pour simuler le comportement du tensioactif dans un large domaine (10-4 à 10-1 mole/l) et de quantité injectée. Ce modèle est utilisable pour évaluer à la fois le comportement des alphaoléfinésulfonates commerciaux en milieu poreux et la faisabilité du procédé

Sandy soils are one of the most widely distributed soils in the world. However, crop production on these soils can be problematic especially in terms of water and nutrient retention. In the face of climate change and a projected reduction in water availability, food production is likely to be particularly affected. The aim of this research is to examine if amending soils with clay and organic matter can improve their water and nutrient retention. The research approach employed laboratory column leaching experiments, rainfall simulation, Computed Tomography (CT) scanning and field trials to investigate the potential of two types of clay, Kaolin (K) and Bentonite (B), and peat (Pt), as well different combinations of clay and peat, to act as effective soil amendments. The influence of amendment materials was assessed by examining water retention, nutrient retention, soil organic carbon and changes in soil properties. Laboratory analysis was supported by field trials to examine the productivity of spring wheat. The results showed that the amendment materials increased soil water retention and availability, reduced water infiltration, increased nutrient uptake, increased spring wheat growth and yield, and improved soil carbon storage compared to an unamended control. The findings provide a further understanding of how the addition of clay and OM can affect ecological function of sandy soils and elucidate the mechanisms involved in controlling water retention and availability, as well as nutrient retention in the amended soils.

Long term storage of bauxite residue materials requires a capping stratum which will limit erosion while stabilizing slopes, limit deep infiltration of water into storage piles, and be aesthetically acceptable to the surrounding community. A diverse native vegetative community capable of surviving seasonal drought, low plant available water and nutrient constraints has the best potential of satisfying most, if not all of these requirements. Current and past rehabilitation of residue disposal areas (RDAs) using species native to southwest Western Australia has exhibited varying success. Current practices at Alcoa World Alumina Australia’s (Alcoa) Western Australia refineries have bauxite residue fines (< 150 ìm) stored within impoundments, in which the outer embankments are constructed with bauxite residue sands (> 150 ìm). The residue sands are also used as the growth media in the capping stratum for vegetation establishment on the disposal sites. Despite the inherently hostile properties of residue sand (pH > 10, EC(1:5) > 4 dS m-1, and ESP > 50), reductions in alkalinity (pH), salinity (EC) and sodicity (ESP) are corrected, through freshwater leaching, to a greater extent than is possible with residue fines. Although leaching can reduce the hostile character of residue sand, additions of phosphogypsum are typically added to expedite the removal of Na and alkalinity, and inorganic fertilizers are incorporated to improve the nutrient status of the growth media. However, due to the inconsistencies in vegetation establishment, which are attributed to poor water retention, inherent nutrient deficiencies and rapid loss of nutrients within residue sands (because of high hydraulic conductivity), further amendments are required. The aim of this study was to determine if amending the residue sand capping layer with residue fines would enhance its overall growth potential for vegetation establishment. Additions of fines to residue sands were predicted to increase water retention, add nutrients and increase the ability of the growth media to retain nutrients. Comparisons were made between the treated residue fines (seawater washed, carbonated, or unaltered) at a series of fines additions (1 - 20 % w/w) and a control(residue sand) amended with 2% (w/w) phosphogypsum and inorganic fertilizer. Comparisons were to determine the differences in 1) water retention, 2) nutrient concentrations and nutrient retention, and 3) plant growth responses and plant biomass nutrient concentrations between the growth media treatments. Four experiments were set up to measure differences in these variables which included: a glasshouse study involving the growth of Acacia saligna; a germination and emergence study (A.saligna); a two year field study in Western Australia; and a glasshouse column leaching study. Water retention increased with increasing percentage of residue fines addition. Plant available water (PAW) increased up to 110 %, with a 20 % increase in fines, representing an increase of 0.026 m3 PAW m-3 residue growth media, when compared to the residue sand only. This increase in PAW was attributed to changes in pore space distributions, due to the increasing fines contents altering the sandy texture to loamy sand texture class. However, initially much of this increase in PAW may not be realized, due to estimated temporary increases in osmotic potential associated with the high salt contents of residue sand and fines. Fines materials have much greater salt contents, and thus need to be leached to a greater extent than sands to remove the associated osmotic potential effects. Essential plant nutrients (P, K, S, Ca, Mg, and B) were increased with additions of residue fines in the glasshouse studies, although many nutrients (Mg, Zn, Mn and B) were still marginal for sustainable plant growth and development. Seawater treated residue fines additions produced the greatest increases in growth media nutrients with substantial increases in soluble (> 7 mg L-1) and exchangeable (> 0.10 cmolc kg-1) Mg, being up to 400 % greater than all other treatments. Along with these necessary nutrients, concentrations of Na were also increased in all fines additions treatments. Added Na may offset the benefits of fines additions, at least in the short term, due to inhibitions of cation uptake from Na competition. However, in the column leaching study soluble and exchangeable Na was lost rapidly from the profile, due to Ca and K displacement of Na from exchange sites during leaching. Soluble Na was removed from the profile to < 5 % of initial concentrations, after only three pore volumes of leaching, and exchangeable Na was removed from charge sites to less than 25 % of the initial concentration. Fines additions did increase concentrations of Mg and K on exchange sites, thus reflecting increased nutrient retention capacity relative to that in residue sand only. Plant growth responses and plant biomass nutrient concentrations were altered with the additions of residue fines to residue sands. The germination and emergence study demonstrated that the emergence of native seedlings was affected by additions of fines, due to the increased salinity and sodicity of the materials. Acacia saligna seedling emergence was inhibited by EC(1:5) > 2 dS m-1, which was highly correlated with a Na/Ca ratio of > 40, for all treatments, except the seawater fines additions. Seeds sown in seawater treatments emerged from growth media with EC(1:5) as high as 3.33 dS m-1 and appeared to be better correlated with Ca/Mg ratios than any other variable. Native vegetation growth responses showed mixed results in fines treated residues in the field. In the greenhouse study, plant growth tended to decrease with fines additions. Poor plant growth with increasing fines additions occurred despite the increased water retention and increased nutrients. This was attributed to the addition of Na associated with the residue fines, as increases in Na, EC and ESP in fines treatments all appear to have limited growth of Acacia saligna in the glasshouse over three months. Seawater fines additions had elevated Mg and B concentrations in plant biomass, and performed better than the carbonated or unaltered fines treatments, but still had reduced growth compared to the residue sand, which contained lower Na concentrations. Additional plant growth limitations may have occurred, due to possible plant nutrient deficiencies including: Mg, Zn, Mn and B and Na toxicity. Incorporation of residue fines into residue sands did increase water retention, nutrient concentrations and the nutrient retention capacity, but did not enhance the overall growth potential for vegetation, at least in the short term. Reductions in germination and emergence of seedlings and reduced plant growth were attributed to increases in Na concentrations introduced from the fines. Seawater washed residue fines had lower ESP and greater concentrations of nutrients, thus reducing the negative impacts from the additional Na introduced, and showed the greatest promise as a fines amendment. As leaching occurs over the first few initial months of rehabilitation, it is expected that the majority of the Na will be removed, from a system with an addition of 5 to 10 % fines, and the positive benefits of the fines additions will than be realized. Findings also illustrate that delaying the planting of vegetation on RDAs, until adequate leaching has occurred to reduce the Na concentrations, will substantially increase vegetation emergence and establishment.

Every day, children are removed from their homes of origin by Children & Family Services and placed into foster care. When the county foster homes become full, private foster family agencies are relied upon to take in the overflow. For a variety of reasons, private agencies are finding it increasingly difficult to recruit and retain sufficient numbers of foster parents to house all of these children. This is a pressing problem in the social work field as, without proper placement options, many children will simply fall through the cracks in the system. The purpose of this research was to explore and address the many concerns surrounding foster parenting, thereby improving foster parent recruitment and retention. Surveys were completed by foster family agency staff (both private and county), current and former foster parents, and people who have considered foster parenting but later changed their minds. Qualitative data gleaned from these surveys revealed improvement that could be made in foster parent recruitment and retention for both private and county agencies. This research has the potential to increase the pool of available foster homes and save the lives of many children.

The purpose of the study was to identify factors affecting student retention at King Saud University in Saudi Arabia. It has been estimated that 35% of university students leave higher education before completing their studies (Al-Saud, 2006). This study was guided by Tinto’s (1975) Student Integration Theory. Berger and Braxton (1998, p. 104) have stated that Tinto’s integration model ‘has been the focus of much empirical research and has near-paradigmatic status in the study of the college student departure.’ This theory is longitudinal and dynamic and views student retention decisions largely as the results of interactions between the student and the academic and social systems of the institution (Tinto, 1975, 1993). This study used a mixed methods approach. Using the terminology of Creswell (2003), the appropriate description of the overall design of this study is a mixed methods concurrent triangulation strategy. This means that ‘qualitative and quantitative data are collected and analyzed at the same time. Priority is usually equal and given to both forms of data. Data analysis is usually separate, and integration usually occurs at the data interpretation stage’ (Hanson et al., 2005, p. 229). This strategy was selected because it allows the findings to be confirmed, cross-validated, and corroborated within a single study (Creswell, 2003). This strategy consisted of two phases. The first phase was the quantitative approach. Quantitative data were collected from 414 freshman students using two questionnaires administered on two occasions and from the university admission office. The quantitative data were analysed using a structural equation modelling (SEM) technique using the AMOS software package. The results of the SEM indicated that Tinto’s model were not useful in predicting the Saudi freshman student retention process. The variables in the model explained only 30 percent of the variance in student retention. The results of the SEM indicated that four of the nine hypotheses proposed in Tinto’s model were supported by statistically significant results. Moreover, only three variables had direct effects on retention. The largest direct effect on retention was accounted for by initial goal and institutional commitment (0.49), followed by later goal and institutional commitment and pre-college schooling as measured by high school scores (0.10). The second phase of this study utilised a qualitative approach. Qualitative data were obtained from three sources: non-persister students, persister students, and staff members. Seventeen non-persister students were interviewed over the phone; 15 persister students were interviewed using a focus group technique; while staff members were asked to complete a survey. Of the 200 surveys distributed, 37 were returned including responses from 16 lecturers, 12 administrators, 5 librarians and 4 academic advisors. A comparison was made between those students who persisted and those who dropped out using constructs from Tinto’s theory. In relation to students’ levels of goal and institutional commitment, it was found that persister students appeared to be more motivated and to have higher levels of goal commitment than non-persister students. Similarly, persister students appeared to have higher levels of institutional commitment than non-persister students, in part it is suggested, due to the fact that the majority of persister students had been able to select their desired majors whereas the majority of non-persister students had not. In relation to the students’ levels of academic integration, there was no significant difference between both groups of students. Persister and non-persister students both exhibited low levels of academic integration into the university system. In addition, there was no significant difference between both groups of students in terms of social integration. Both groups of students indicated low levels of social integration into the university system. In addition, the participants (persister students, non-persister students, and staff members) were all asked to indicate what they perceived to be the major factors affecting student retention at King Saud University. The findings from the qualitative data not only help to explain and confirm the quantitative findings but also identify why Saudi freshman students leave the university before completing their studies. The most important factors were: difficulties of selecting majors, difficulties of transferring between subjects, lack of academic advice and irregularity of monthly reward.

L'utilisation, en centres de stockage de dechets, de materiaux deformables partiellement satures comme barrieres etanches rend necessaire la caracterisation de leurs proprietes hydrodynamiques, en particulier leur permeabilite. Ces dernieres sont examinees ici sous trois angles analytique, experimental et numerique. Si l'on suppose applicable la loi de darcy pour des milieux faiblement permeables, le transport de l'eau en milieu deformable peut etre modelise de maniere equivalente en coordonnees spatiales (formalisme eulerien) ou materielles (formalisme lagrangien). Les equations de transferts ainsi etablies relient les trois relations fonctionnelles retention, conductivite hydraulique et courbe de gonflement. L'analyse de l'infiltration en milieu non sature, tenant compte du chemin de deformation, permet alors d'introduire le concept de sorptivite apparente de la phase solide, complementaire de celui de sorptivite capillaire. Des techniques experimentales, de laboratoire (spectrometrie gamma double energie) et de terrain (infiltrometries a disques et a anneaux), sont ensuite appliquees a l'etude en regime transitoire de l'infiltration dans des materiaux compactes naturels (argiles) et artificiels (melange sable-bentonite). Enfin, les phenomenes experimentaux observes sont reproduits numeriquement a l'aide du code informatique wisp developpe pour l'occasion. Celui-ci permet l'etude des facteurs clefs de l'ecoulement en milieu peu permeable. Des differents resultats obtenus selon ces trois approches, on conclut que la capillarite est de loin le principal moteur du transport dans le type de milieux consideres. On montre par ailleurs que la prise en compte du gonflement et la bonne connaissance du chemin de deformation sont indispensables a une estimation correcte des proprietes hydrodynamiques.

L’ordonnance du 23 mars 2006 a réformé le droit des sûretés en France et introduit un gage sans dépossession inspiré du security interest américain dans l’objectif d’améliorer l’efficacité de la matière. L’amélioration est visible mais peut encore être approfondie. En premier lieu, la prépondérance de l’autonomie de la volonté dans la constitution et le régime du gage sans dépossession traduit son détachement progressif de la matière réelle. En effet, le droit du créancier bénéficiaire a pour objet plus la valeur du contenu de l’assiette affectée que son incarnation matérielle. Ainsi, il faut, d’une part, autoriser l’évolution du contenu matériel de l’assiette de constitution pour admettre que l’assiette de réalisation ne soit pas constituée des mêmes biens mais représente toujours la même valeur affectée. D’autre part, il faut reconnaître l’opposabilité du droit de rétention fictif aux procédures d’insolvabilité. En second lieu, le détachement de la sûreté de son objet réel et la prévalence de l’autonomie de la volonté doivent se prolonger en droit international privé. Ainsi, il convient d’admettre l’abandon de la compétence de la lex rei sitae, source de difficultés liées à la nature mobilière du bien grevé, et de reconnaître la compétence de la lex contractus, tirée de la prépondérance de la source conventionnelle de la sûreté.Ainsi, tant l’adaptation de la sûreté permise par la place laissée la volonté des parties, que la possibilité de circulation transfrontalière offerte par la reconnaissance des sûretés étrangères, font du gage sans dépossession une sûreté plus efficace aussi bien en droit interne qu’au niveau international
On March 23rd 2006, the French reform of security law introduced the « gage sans dépossession », inspired by the security interest of the Article 9 of the U.C.C. from the United- States, in order to improve the efficiency of security law in France. The enhancement is undeniable and yet but there remains room for improvement.First of all, the increased autonomy given to parties when creating and ruling a security results in its detachment from the scope of personal property. Indeed, the creditor is more entitled to the value of the collateral rather than to the good itself. Therefore, the physical content of the collateral should be allowed to change physically as long as collateral remains of same value. On the other hand, the creditor’s fictive right of retention must be enforceable against insolvency proceedings. Secondly, both the detachment of the security from its physical collateral and the preponderance of parties’ autonomy must be taken into account in international private law. Should a matter of choice of law arise, the security should be governed not by lex rei sitae, given the issues raised when applied to movable goods, but by lex contractus, on account of the contractual source of the security. As a result of its adaptability enabled by autonomy, and as a result of the ability to move the security over borders and still be enforceable, the French “gage sans dépossession” appears to be more efficient both in France and on an international level

Thesis (M.S.)--University of Wisconsin--Madison, 1995.
Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 49-52).

This study tried to evaluate the veracity of Grant and Groenevelt (2015) assertion that the inflection point on the water retention curve (WRC), plotted on semi-log scale, marks the onset of hydraulic stress in plants grown in sandy soils. That is, as the soil dries during drainage and evapotranspiration, there comes a point (argued to be the inflection point) when the unsaturated hydraulic conductivity cannot keep up with plant demand for water; thus, plants begin to suffer. Interest in the inflection point stemmed from the need to find unbiased criteria to weight the water capacity downward in the integral water capacity (IWC) model of Groenevelt et al. (2001) to account for soil hydraulic restrictions. If the inflection point was truly a good indicator of the onset of plant stress, then the matric suction at this point can easily be found from the fitting parameter, kₒ (m), in Grant and Groenevelt (2015) water retention model; by coincidence it can also be found from the fitting parameter, 1/α (m) in the water retention model of (Van Genuchten 1980). The experimental components of this study consisted of two main parts: In the first part, water retention curves for a range of different sands and sandy soils were prepared, their inflection points identified, and two points on either side of the inflection point (wetter and drier) identified (Chapters 3 and 4). In the second part, wheat plants were grown in a glasshouse to Zadoks et al. (1974) growth stage 21 in pots of the different sands held, constant, at three different soil water suctions: at, above and below the inflection point (Chapter 5). Detailed water retention curves were prepared using multiple replicates (up to 20) of four sands and two sandy soils (Very coarse sand, Coarse sand, Medium sand, Fine sand, Very fine sand, and Sandy loam) placed in small rings on ceramic pressure plates at different matric suctions ranging from saturation to 25 kPa or greater. Each of the individual sets of water retention data (up to 20) were fitted to the water retention models of Groenevelt and Grant (GG), and Van Genuchten (VG), and the inflection points identified from the appropriate fitting parameters. As might be expected, the different models produced slightly different inflection points, but these indeed corresponded pretty well (but not precisely) with kₒ and 1/α respectively. There was a strong inverse correlation between the mean particle size of the sands and sandy soils, and the values of kₒ and 1/α; that is, the inflections points shifted to greater matric suctions as mean particle size decreased, such that the Very coarse sand had the smallest values of kₒ and 1/α while the Sandy loam had the largest values of kₒ and 1/α. Because the VG model fitted the measured water retention data slightly better than did the GG model, the parameters from the VG model were chosen to identify the soil water conditions for the plant experiments. The matric suction at the inflection point, hᵢ (m), was identified from 1/α, and this corresponded with the maximum differential water capacity, C(hᵢ). The wetter, hw, and drier, hd, matric suctions were chosen to correspond with the matric suctions at 90 % of the maximum differential water capacity (on either side of the inflection point). The value 90 % was chosen as being close to the inflection point yet falling outside its 95 % confidence interval. The (up to) 20 estimates of hw, hi and hd were used to identify the corresponding volumetric water contents directly from the water retention curves, and these were averaged and converted to gravimetric water contents that could be used to set up the soil water conditions in the pot study. Following a 6 x 2 x 3 completely randomised factorial design, litre-sized pots of each sand or sandy soil (5 replicates) were set up at the three different water contents corresponding to hw, hi and hd, (covered in plastic beads to minimise evaporation) and wheat seeds (2 different genotypes) planted and grown in them to growth stage 21. To keep soil water contents constant, daily pot weights were recorded and then water added (calibrated for increasing plant mass over time) to replace water evapo-transpired. The measure of plant response to the soil water conditions was the mass (fresh and dry) of shoots and roots. Although one of the wheat genotypes performed significantly better than the other (consistent with the literature), the F-test or analysis of variance (ANOVA) indicated that the wheat genotypes never responded to the soil moisture conditions or matric suction effects at or surrounding the inflection point. Possible reasons for the lack of response to the soil moisture conditions may be related to the choice of the wet and dry-side matric heads, particularly on the dry side; that is, the matric suction on the dry side of the inflection point, which corresponded to 90 % of the maximum water capacity, may not be sufficiently dry to induce a hydraulic stress. Contrast to this, was the source of variation that arose from the three and two factor interaction effects on the dry weights of shoot and root respectively, which showed significant differences. However, this was not convincing enough for one to accept the null hypothesis of the study due to the inconsistent nature of trends observed in the dry weights obtained at or surrounding the inflection point matric suction. On this basis, the importance of the inflection point as a marker of hydraulic stress in plants is not rejected at this stage – further research is needed.
Thesis (M.Phil.) -- University of Adelaide, School of Agriculture, Food and Wine, 2017

Natural coarse textured soils comprise a significant portion (approximately 20%) of the area to be mined at Suncor, Syncrude (aurora mine), Albian/Shell, and CNRL mines in the Alberta’s oil sands (Macyk, 2006). Although similar in soil textural classifications, the undisturbed areas support a range of ecosite types which exhibit different moisture regimes, suggesting that there are natural mechanisms controlling the plant available water sufficient for forest development. The global objective of this study was to evaluate the potential for textural variability to enhance water storage in coarse textured soil. The observations of the infiltration and drainage behaviour of natural and reclaimed coarse-texture soils in this study have demonstrated that this potential exists and can be applied in reclamation design to achieve the ranges of soil water storage needed to establish different ecosites. Field based infiltration and drainage testing, pit excavation and sampling have been completed on 14 sites (7 natural and 7 reclaimed). Bulk saturated hydraulic conductivity and field capacity were estimated for each of the 14 sites based on the field test results. The observed transient water dynamics give an indication of the effect of layering on these material properties. Laboratory analysis of water content (650 samples), particle size (650 samples), water retention (35 samples), organic carbon (100 samples) as well as calibration of field instrumentation were completed on a large number of samples (approximate values shown in brackets above) across all sites. The laboratory analysis was used to characterize textural variability (mean and standard deviation of the particle diameter) for the layered sites and estimate the soil water retention curve (SWRC) relationships for the range of soil textures encountered at the study sites. Pedotransfer functions (PTFs) were used to investigate if there were significant differences in the residual sum of squares between estimated and measured SWRCs. The measured organic carbon was used to aid in estimating permanent wilting point (WP) used in the calculation of the available water holding capacity (AWHC) of all profiles. An investigation into the calibration of the moisture capacitance probe (MCP) was undertaken as part of a comparison of the measured and simulated volumetric water content (VWC) profiles. Water storage at the cessation of drainage was related to the soil texture and textural variability as measured in the laboratory. Sites with more textural variability generally stored more water for plant use. There appeared to be a limit to what can be considered ‘useful’ textural variability. If adjacent soil layers had too extreme a contrast in texture and therefore hydraulic conductivity, unstable/preferential flow (i.e. bypassing of some of the water and nutrients from plant roots) occurred. The total porosity calculated from field samples was often higher than the maximum measured VWC in each layer which may be indicative of one or more factors that resulted in less than full saturation being attained within the targeted 1 m depth of saturation during the test. Some of these factors include: errors in sampling leading to an overestimate of total porosity; lateral flow along textural interfaces; air entrapment within the rapidly advancing wetting front; unstable/preferential flow as a result of the high contrast in hydraulic conductivity (fine over coarse) between adjacent layers (i.e. Ks Ratio >20) or where tests were conducted on slopes (i.e. funnel flow). This latter case was common at the reclaimed sites. A modelling study of one uniform (SV10) and one layered (NLFH1) natural site was conducted. The models were built by incorporating soil properties of the layers in the various soil profiles as estimated from field and/or laboratory testing. This study offers a comparison between various PTFs and their ability to capture the soil-water storage/dynamics during infiltration and drainage testing. The Arya PTF gave a better estimation of the laboratory measured SWRCs. However, when modeling the measured infiltration and drainage testing for the relatively uniform site SV10, the Arya PTF and Modified Kovacs (MK) PTF performed similarly. The Arya PTF performing slightly better for the infiltration phase and the MK PTF performing slightly better for the drainage phase. Both PTFs gave a reasonable estimation of water storage but the MK PTF gave a better estimation of the water storage with time as compared to the Arya PTF. For the highly layered site NLFH1, neither model performed well. The Arya PTF gave a substantially better estimation of the infiltration phase and gave the better estimation of the magnitude of water storage with time, the MK PTF performed marginally better for the drainage phase and gave a better estimation of the shape of the water storage with time. Generally, the study showed that the replication of the profile water storage requirements for the layered natural ecosites (‘b’ and ‘d’ ecosites) has been achieved and can be achieved by layering (or even mixing) available coarse textured reclamation materials. This study has indicated that replicating the highly uniform ecosites (‘a’ ecosites) is where the bigger challenge lies in reclamation. Reclaiming with a diversity of target ecosites is essential to achieving the pre-disturbance land capability standard that the mine operators are bound by. The temptation may exist to simply condone reclamation that has met or exceeded the pre-exisiting land capability. However, problems with ground water recharge and regional water distribution are likely to arise if large areas of lower functioning ecosites are replaced with higher functioning ecosites.