Dissertations / Theses on the topic 'Relative compaction'

Soil compaction often limits conifer regeneration on sites degraded by construction of landings and roads, but inadequate understanding of compaction characteristics has sometimes led to inappropriate rehabilitation efforts. This warrants development of new methods to assess compaction and its relation to tree growth. The objective of this study was to develop a high-level integration indicator that will characterize compaction of forest soils and that could be correlated to tree height growth. Mineral particle density of soils from interior British Columbia (BC) forests varied significantly among the geographic locations. Oxalate-extractable Fe- and Al-oxides and particle size distribution (PSD) were related to soil and mineral particle densities, while soil organic matter (SOM) and Al- and Fe-oxides were important soil properties in relation to soil particle density. The significance of levels of single soil properties in predicting maximum bulk density (MBD) were in the order: plastic and liquid limits, organic matter content, oxalate-extractable oxide, and PSD. Stratification of the sample according to Atterberg limits improved the predictability of MBD, and variation in particle density was included in the prediction by other soil properties used in the models. Height growth of interior Douglas-fir (Pseudotsuga menziesii var. glauca [Bessin] Franco) was restricted when relative bulk density (RBD) was > 0.72. For lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) and hybrid white spruce (Picea glauca [Moench] Voss × engelmannii Parry ex Engelm.), an RBD of 0.60 - 0.63 corresponded to maximum height growth, while that of 0.78 - 0.84 appeared to limit height growth. The presence of surface organic material mitigated compaction and was often associated with lower RBD. Interior Douglas-fir and lodgepole pine planted in low elevation sites in north-central BC did not grow well and their height growth was weakly related to RBD. The results suggest that soil rehabilitation should be considered on disturbed sites where soil RBD is > 0.80. Findings in this study have implications in assessing forest soil compaction and its effect on site productivity. The results will help predict soil behaviour and associated tree growth in response to timber harvesting and site rehabilitation.

Large scale static lateral load tests were completed on a pile cap with wingwalls under several different sand backfill configurations: no backfill, loosely compacted unconfined, loosely compacted slip plane wall confined, loosely compacted MSE wingwall confined, and densely compacted MSE wingwall confined. The relative compaction of the backfill was varied during each test to observe the change in passive resistance provided by the backfill. The wall types were varied to observe the force placed on the walls and the wall displacement as a result of the laterally loaded pile cap and backfill relative compaction. Passive force-displacement curves were generated from each test. It was found that the densely compacted material provided a much greater passive resistance than the loosely compacted material by 43% (251 kips) when confined by MSE walls. The outward displacement of the MSE walls decreased noticeably for the dense MSE test relative to the loose MSE test. Backfill cracking and heave severity also increased as the relative compaction level of the backfill increased. As the maximum passive force was reached, the reinforcement reached their peak pullout resistance. Correlations were developed between the passive pressure acting on the pile cap and the pressure measured on the MSE wingwalls as a function of distance from the pile cap for both loose and dense backfills. The pressure measured on the wingwalls was approximately 3 to 9% of the pressure acting on the pile cap. As the distance from the pile cap increased, the pressure ratio decreased. This result helps predict the capacity of the wingwalls in abutment design and the amount of allowable wall deflection before pullout of the backfill reinforcement occurs. Three methods were used to model the measured passive force-displacement curves of each test. Overall, the computed curves were in good agreement with the measured curves. However, the triaxial soil friction angle needed to be increased to the plane strain friction angle to accurately model both the loose and dense sand MSE and slip plane wall confined tests. The plane strain friction angle was found to be between 9 to 17% greater than the triaxial friction angle.

The majority of therapeutic pharmaceutical formulations are presented in the solid form. Moisture is able to play an important role in the functional performance of pharmaceutical solids. Moisture profiling is able to provide novel information with regards to the behaviour of moisture within materials using equilibrium relative humidity as a measurement. The hypothesis investigated explores the changes in equilibrium relative humidity of pharmaceutical material induced by physical, chemical or storage conditions, these are able to be monitored using the innovative moisture profiler system. The aims within this were to primarily validate the moisture profiler and secondly evaluate the effects of moisture on physical forms and with respect to effects of compaction, finally this was compared to conventional characterisation methods. Preliminary explorations were conducted in order to assess the validity of the moisture profiler, from this lactose was selected as a suitable pharmaceutical material for further work. Processing effects were then examined, firstly storage at elevated relative humidity of different forms of lactose were explored, and this was carried out with supplementary analysis. Secondly the effects of tabletting were explored, different compaction forces were investigated to observe if this had any notable effects on equilibrium relative humidity of the different lactose forms. Finally subsequent storage of the compacts were examined in order to explore if there were any changes in the equilibrium relative humidity.

A uniaxial High-Velocity Compaction (HVC) process for polymer powder using a cylindrical, hardened steel die and a new technique with relaxation assist was tested with a focus on the compactibility characteristics and surface morphology of the compacted materials using various heights of relaxation assist device with different compacting profiles.

Relaxation assist device was presented as a new technique to reduce springback, pull-out phenomenon and to improve the compaction process.

The basic phenomena associated with HVC are explained and the general energy principle is introduced to explain pull-out phenomenon during the decompacting stage. In this study, polyamide-11 powders with different particle size distributions have been compacted with the application of different compaction profiles, e.g. different energies and velocities. It was found that the relative green density is influenced more by the pre-compacting (primary compaction step) than by the post-compacting (secondary compaction step).

Experimental results for different compaction profiles were presented showing the effect of varying the opposite velocity during the decompacting stage and how to improve the homogeneous densification between the upper and lower surface and the evenness of the upper surface of the compacted powder bed by using relaxation assists, and the influences of the relaxation assist device on the process characteristics. It was found that the relaxation assist improves the compaction of the polymer powder by locking the powder bed in the compacted form. In addition, the relative times of the compacting stage, decompacting stage and the reorganisation of the particles can be controlled by altering the height of the relaxation assist. It was found that the high-velocity compaction process is an interruption process and that the delay times between the pressure waves can be reduced by increasing the height of the relaxation assist device. Furthermore, the first gross instantaneous springback and the total elastic springback are reduced.

Two bonding strain gauges and a high-speed video camera system were used to investigate the springback phenomenon during the compaction process. Scanning electron microscopy (SEM) and image computer board Camera (IC-PCI Imaging Technology) were used to the study the morphological characteristics, the limit of plastic deformation and particle bonding by plastic flow at contact points, and pull-out phenomena.

QC 20100506

L'objectif de ce travail a été d'étudier l'effet de la compaction du sol sur l'activité photosynthétique, la répartition des assimilats et la morphologie du maïs en phase de croissance végétative, jusqu'à la sortie de la panicule mâle. Nous nous sommes en particulier intéressés à la rhizodéposition du carbone et à ses conséquences sur la biomasse microbienne du sol. Nous avons comparé des plantes cultivées dans des pots contenant un mélange de terre et de sable (2/1) présentant deux densités apparentes : 1,45 g cm-3 pour le sol compacté et 1,30 g cm-3 pour le témoin. Les expériences ont été conduites dans un phytotron pendant 21 à 42 jours. La répartition du carbone a été établie à l'aide des techniques de marquage court au 14 C. La densité apparente élevée du sol induit une diminution de l'activité photosynthétique et de la quantité de carbone fixée. La compaction du sol provoque un ralentissement du rythme d'émission foliaire, réduisant ainsi la hauteur des plantes, la biomasse des parties aériennes et la surface foliaire. La biomasse et la longueur racinaires sont inférieures chez les plantes subissant la compaction du sol. Simultanément, une forte augmentation de la rhizodéposition est observée dans le sol compacté. Ainsi, la biomasse microbienne du sol augmente fortement grâce à l'abondance de substrats, carbonés et à la protection physique que la compaction assure à la microflore en réduisant la porosité du sol. Pour expliquer ces résultats, nous avons émis trois hypothèses : 1- une diminution du potentiel hydrique ou une limitation de la force de puits. Des racines est à l'origine de la baisse de l'activité photosynthétique, 2- l'expansion du diamètre racinaire permet de surmonter la résistance du sol à la pénétration et 3- l'augmentation de la libération du carbone dans le sol réduit les effets de la contrainte mécanique. Les effets de la compaction persistent avec l'âge des plantes bien qu'ils diminuent en termes de pourcentage entre les deux traitements
The objective of this work was to investigate the effects of soil compaction on carbon assimilation, photosynthate partitioning, and morphology of corn plants during vegetative growth period up to tassel initiation. We were particularly interested in carbon input into the soil and soil microbial biomass. Corn plants were grown in culture pots containing compacted soil (bulk density of 1. 45 g cm-3 ) or loose soil (bulk density of 1. 30 g cm-3). Experiments were conducted in a growth chamber and lasted for 21 to 42 days. Carbon partitioning in the plant-soil system was evaluated using 14C pulse-labeling techniques. The increase in soil bulk density decreased carbon assimilation rate and total carbon fixation. Furthermore, soil compaction delayed leaf appearance rate decreasing therefore plant height, shoot dry weight, and leaf area. In addition, root biomass and root elongation were also inferior when plants were grown in compacted soil and root length appeared to be the most sensible parameter to high soil mechanical resistance. Simultaneously, a great increase in carbon input into the soil occurred to the detriment of root carbon. Soil microbial biomass increased considerably in compacted soil thanks to this increase in carbon substrates and to physical protection provided for soil microflora as a result of the reduced porosity in compacted soil. Three hypotheses were formulated to explain these results: 1- a decrease in soil or root water potential or a sink limitation induces a down-regulation of photosynthetic activity, 2- the increase in root diameter decreases soil mechanical resistance, and 3- the increase in carbon rhizodeposition alleviates the effects of mechanical constraint. The effects of soil compaction persisted with plant age although the difference between the two treatments decreased in terms of percentage

Ever-growing discharges of various emerging chemical contaminants are imposing a great threat of pollution to the coastal environment. Adsorption by sediment plays an essential role in the transport and fate of pollutants in the aquatic system. The sorption of emerging contaminants onto sediment is believed to be largely dependent on the sediment organic matter (SOM). In the present study, laboratory experiments were carried out on the changes of the adsorption behavior of sediment during the sediment aging and diagenesis process. A few EDCs and antibiotics were selected as the model emerging compounds for the adsorption tests. The results demonstrated that both the quantity and the quality of the SOM affected the adsorption of the model pollutants, such as 17α-ethinyl estradiol (EE2) and bisphenol A (BPA), onto the marine sediment collected from Victoria Harbour, Hong Kong. The adsorption isotherms can be well described by the linear partition model. Natural and artificial sediment with a high SOM content was incubated for 4-6 months to simulate the natural diagenesis process. The most rapid degradation of labile SOM occurred in the first 1 month or so and afterward, SOM reduction became slower. Microbial activity played an important role in SOM degradation and transformation. A rapid initial bacterial growth was observed in the sediment, followed by a slow endogenous decay. The dynamics of biomass growth and decay first transformed the labile SOM into biomass and microbial byproducts. After the exhaust of readily biodegradable SOM, the biomass decay produced humic-like substances, resulting in more refractory and condensed SOM residues in the sediment. More importantly, the degradation and transformation of SOM displayed a profound impact on the adsorption behavior of the sediment. For the selected EDCs and antibiotics, including BPA, EE2, nonylphenol (NP), phenanthrene (PHE) and tetracyclines (TCs), the adsorption capacity indicated by the partition coefficient, Kd, decreased at the beginning of SOM diagenesis. The Kd values for different chemicals recovered lately to different extents as the result of the SOM condensation and humification. All of the organic matter normalized partition coefficients, KOM, of the concerned pollutants increased considerably in the late phase of SOM diagenesis. Based on the experimental results, a general conceptual model was established to describe SOM diagenesis and its impact on chemical adsorption by the sediment. According to the model prediction, the SOM profile would become more dominated by the condensed and refractory fractions during sediment diagenesis with an increasing affinity and partition capacity for organic contaminants. Moreover, the release of adsorbed contaminants from marine sediment in the simulated digestive fluids was investigated. In general, the presence of gastric pepsin and bile salts helped the desorption of hydrophobic pollutants from the sediment into the digestive solutions. The influence of the SOM diagenetic status on chemical desorption from the sediment varied between EDCs of different chemical properties. It is apparent that aged sediment could bring more emerging pollutants into the digestive system of receiving organisms, imposing a potential risk to human health through the food chain.
published_or_final_version
Civil Engineering
Doctoral
Doctor of Philosophy

Increased snowmobile use in mountainous terrain has been highlighted as a conservation concern for some Canada lynx (Lynx canadensis) populations. Snow compaction resulting from winter recreation may potentially facilitate access by coyotes (Canis latrans) to habitats used by lynx during winter. Increased interactions could result in either exploitation or interference competition between the two species. Two recent, yet geographically distinct, studies showed contrasting findings regarding coyote movements and their use of snow-compacted trails during the winter. These findings suggest coyote association with snow-compacted trails may be regionally specific and dependent upon ecosystem dynamics and snow characteristics. The objectives of this study were to document diet, space use, and movements of coyotes occupying deep snow regions and explore whether a potential existed for increased interactions between coyotes and lynx due to snowmobile activity. We documented seasonal variation in coyote diets using scat collections to assess dietary overlap with lynx. Coyote resource use within and among habitats containing snowmobile activity was examined using coyote backtrack surveys during two consecutive field seasons in northwestern Wyoming. Although scat analysis findings suggest dietary overlap was not significant between coyotes and lynx during the winter or overall (all seasons combined), we lacked adequate sample size of lynx scats to determine if dietary overlap occurred during the fall, when coyote use of snowshoe hare peaked (24.1 % of all fall occurrences). Coyote backtrack surveys revealed that coyotes not only persisted in habitats used by lynx throughout the winter, but that snow compaction resulting from winter recreation use appeared to influence coyote movements during the winter months. Microhabitat analysis revealed that snow conditions influenced coyote behaviors and habitat use. This research provided insight into the impacts of winter recreation on coyote diet and habitat use during the winter months in northwestern Wyoming. In addition, these results have implications for local lynx populations in the southern periphery of their natural range. These results may assist land management agencies in planning and implementing management strategies to enhance lynx recovery, and may be used to guide decisions regarding areas designated for winter recreation and areas proposed for expansion of winter activities.

Roadside verge vegetation is a complex, unusual community, poorly understood and researched and a typical example of a “novel ecosystem”. The land has been altered by humans, the topsoil introduced from elsewhere, a seed mixture added and a management regime implemented. Vegetation is a cost effective, sustainable method for improving slope stability on steeper roadside slopes. On newly constructed roadside verges its rapid establishment prevents soil erosion and provides an aesthetic cover. The standard grass seed mixture sown includes grass species which are quick growing, vigorous and competitive. The belowground root system increases soil strength and the aboveground canopy reduces surface erosion, although soil compaction can restrict root and shoot growth. Morphological differences between grasses and wildflowers allow the root systems to utilise different soil strata and the aboveground canopy to fully exploit aboveground niches. Therefore maybe a species-rich grassland seed mixture should be sown to improve slope stability? The BIONICS Embankment at Nafferton Farm was used to investigate aspect and soil compaction on the establishment of a species-rich grassland. A second smaller Mesocosm experiment investigated the effects of aspect, soil compaction and cutting regimes on the aboveground composition and biomass, and the belowground rooting depths of two different seed mixtures. Also a survey of the plant communities and environmental characteristics of grass cuttings was carried out along the A303 and A38 in Wiltshire and Devon. On the BIONICS embankment 14 generalist plant species germinated from the seed mixture and arable and injurious weeds colonised. More wildflowers, e.g. Lotus corniculatus, grew on the south-facing slopes while more grasses and some herbs, e.g. Ranunculus repens, grew on the north-facing slopes. Ellenberg Indicator Values for fertility and moisture were higher on north-facing slopes, with light values greater on south-facing slopes. Lolium perenne, Medicago lupulina and Achillea millefolium were associated with the less compacted subsoil. In the Mesocosm experiment, L. perenne, Cynosurus cristatus, Phleum bertolonii, Daucus carota, Leucanthemum vulgare, Plantago lanceolata, Rumex acetosa and Sanguisorba minor were common. More wildflowers were found on the south-facing plots, such as L. vulgare and P. lanceolata, whereas the grasses L. perenne and C. cristatus preferred the north-facing plots. Frequent cutting increased species richness and diversity, favoured C. cristatus and L. 4 vulgare and reduced L. perenne and P. lanceolata. Grasses such as L. perenne and P. bertolonii were more reduced by compaction than the wildflowers such as Rhinanthus minor and Trifolium pratense. Plots sown with a mixture of grasses and wildflowers had greater above-ground biomass than the grasses-only plots and on the north-facing aspect had greater biomass than the flat and south-facing plots. Plots just sown with grasses had higher biomass on the flat plots. R. minor did not germinate well in the plots with high biomass but survived in regularly cut plots. Plant roots in the Mesocosms grew down the whole soil profile in all treatments (40 cm). The total root mass was greater in the grasses-only plots in comparison to the grass and wildflower plots. However, the grass roots were smaller and finer, whereas the wildflower roots were bigger, yet lighter. Although the grasses-only plots had greater root mass, these plots had lower aboveground biomass, while the grass and wildflower plots had lower root mass, but greater aboveground biomass. Bulk density (BD) and Penetrometer resistance (CI) was greater in the compacted treatment, although this did not reduce root mass, or reduce aboveground biomass. However, CI was greatest in the flat and south-facing plots where root mass was less, and CI was lower in the north-facing plots where root mass was greater. The roadside survey showed that natural colonisation could produce species-rich habitats over time with 116 species found. Arrhenatherum elatius was the commonest grass, Cirsium arvense and Senecio jacobaea were frequent and scrub encroachment was widespread. These roadside verges were not cut frequently enough to prevent succession into scrub and woodland. Centaurea nigra, L. vulgare and D. carota had higher cover on south-facing slopes, contributing to the higher diversity on this aspect. Signs of bareground and desiccation were greater on south-facing slopes. Grasses were more abundant on the north-facing slopes leading to mesotrophic communities on this aspect. Many sites had a unique and unusual combination of species that didn’t fit into the National Vegetation Classification (NVC). Roadside embankment construction does not hinder the establishment of a species-rich seed mixture, although a regular cutting regime is required of at least once a year to prevent scrub encroachment and to reduce the spread of injurious weeds. A grass and wildflower seed mixture containing a range of functional types will have greater aboveground biomass, with a denser canopy and heterogeneous root system, which will help to prevent surface erosion and runoff and increase soil strength.

La Compaction à Grande Vitesse (CGV) est un procédé efficace pour mettre en oeuvre par frittage, et dans un temps court, des poudres polymères semi-cristallins quelle que soit leur viscosité en partant d’une température inférieure au point de fusion. L’échauffement et la fusion du matériau est obtenu par une succession d’impacts à une énergie donnée ce qui offre la possibilité de définir finement la quantité d’énergie que l’on souhaite apporter au matériau et la qualité du frittage. Une fusion partielle de la poudre permet de profiter de la cristallinité élevée de la poudre native, un compromis est alors possible entre de hautes propriétés élastiques et une ductilité élevée. La contre-partie de cette efficacité est une mise au point délicate du procédé. Dans le cas du polyéthylène ultra haute masse molaire (UHMWPE), il a été montré que le procédé permet une quasi-abstraction des effets de la masse molaire. Le frittage du UHMWPE demande seulement une réorganisation à courte distance des chaînes qui peut se faire dans un temps très limité. La cohésion de la poudre est assurée essentiellement par la cocristallisation et la création de nouveaux enchevêtrements. La modélisation du procédé a permis de comprendre comment l’énergie cinétique lors des impacts est transformée en chaleur dans la poudre et elle a permis l’établissement d’un critère de processabilité par CGV. Ce critère de processabilité repose sur la déformabilité de la poudre contenu dans la matrice au moment de l’impact. Celle-ci doit être suffisante pour que l’énergie dissipée dans le matériau permette sa fusion en moins de cent coups. Ceci a permis de comprendre pourquoi le polyoxyméthylène peut difficilement se mettre en forme par CGV
High Velocity Compaction (HVC) is an efficient process to mold, in a short time, semicrystalline polymers powders any about their viscosity by starting from a temperature below melting point. Heating and melting occur by successive impacts at a preset energy that offers the possibility to set accurately the energy amount that we would bring to the material and the sintering quality. Partial melting of powder enable to take advantage of the high cristallinity of nascent powders, a compromise is possible between high elastic properties and high ductility. The flip-side of this efficiency is a delicate process settings. For the ultra high molecular weight polyethylene (UHMWPE), it has been shown that the process makes it possible a quasi abstraction of molecular weight effects. UHMWPE sintering needs only a short length reorganisation of chains that could be done in a really short time. Powder cohesion is essentially bring by cocrystallisation and by new entanglements creation. Process modelling allowed to understand how kinetic energy during hits is converted into heat in powder and it’s enable to define a HVC processability criterion. This processability criterion rests on the strainability of powder place in a die during a hit. It has to be sufficient to the dissipated energy in material allows his melting in less than one hundred impacts. This criterion allows to understand why the polyoxymethylene is hard to mold by HVC

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Over the past two centuries, coastal wetlands have become increasingly threatened by accelerated relative sea-level rise and anthropogenic modification. Engineered structures such as sea walls, levees, and drainage systems prevent natural processes of sediment distribution, reducing the resilience of coastal ecosystems. Land subsidence and shoreline erosion combine with global sea-level rise to make low-elevation coastal zones increasingly vulnerable to submergence. This dissertation examines processes of sediment accumulation, compaction, and relative sea-level rise in coastal wetlands and assesses strategies for restoration. I find that organic content strongly controls sediment compaction in wetland sediments. At least 80% of compaction happens quickly, largely within the first 100 years after deposition and in the top 1 m of the subsurface. This rapid shallow compaction is generally not recorded by traditional methods of measuring relative sea-level rise in low-elevation coastal zones (i.e., tide gauges and global navigation satellite systems). As a result, tide gauges generally underestimate rates of relative sea-level rise in low-elevation coastal zones and these areas may be at a greater risk of flooding than previously realized. However, despite accelerated rates of relative sea-level rise and rapid sediment compaction, coastal restoration efforts such as river diversions can be successful in building new land in some areas. I find that sediment deposition responds non-linearly to water discharge, reaching a maximum at moderate discharge. Wetlands are more likely to keep up with relative sea-level rise if hydrodynamic conditions are optimized to retain mineral sediment in targeted restoration areas.
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Margaret Keogh

Subband coding schemes have been widely used to encode signals from speech, high quality audio, and image sources. The theory of perfect reconstruction filter banks has also been studied extensively. The purpose of this thesis is to study the properties of the so-called paraunitary systems, and issues pertaining to their applications and implementations. We will begin by proving several properties of paraunitary filter banks. For example, we will prove that all orthonormal discrete-time wavelets can be generated using paraunitary binary trees. We will also extend this result to arbitrary tree-structures and wavelet packets. Next, we will address the two issues involved in the design of a paraunitary subband coding system. 1) the problem of optimal bit allocation among various channels given a fixed bit-rate, and 2) the problem of finding the optimal filter bank (by optimization) to encode a given signal. We will prove several interesting results in this regard. We will then show how generalized polyphase representations can be used to enhance the coding gain of transform coding systems. In practical applications, one often imposes several other conditions on the individual filters in a filter bank. For example, the linear phase property is found to be important for encoding image signals, whereas the 'pairwise mirror-image' property generally yields filters with better responses and, therefore, better frequency selectivity. The final part of the thesis deals with the implementions of paraunitary systems having such additional properties. We will obtain factorizations for such systems which will be proved to be minimal as well as complete. These factorizations yield structures which are robust, i.e., all the desired properties are retained in spite of coefficient quantization.