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The Global ETD Search service is a free service for researchers
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Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
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Showing 41 to 46 of 46 (0.013 seconds)| 41 |
Electrical resistivity measurements of mechanically stabilized earth retaining wall backfillSnapp, Michael Andrew January 1900 (has links)
Master of Science / Department of Civil Engineering / Stacey Kulesza / In Kansas, mechanically stabilized earth (MSE) retaining walls are typically backfilled with coarse aggregate. Current backfill material testing procedures used by the Kansas Department of Transportation (KDOT) utilize on-site observations for construction quality assurance and the American Association of State Highway and Transportation Officials standard T 288-12 (“Standard Method of Test for Determining Minimum Laboratory Soil Resistivity”). AASHTO T 288-12 is designed to test a soil sample’s electrical resistivity (ER) that correlates to its corrosion potential. However, the test, based on material passing through a No. 10 sieve, is inappropriate for coarse aggregate typically used by KDOT as the aggregate will be retained on a No. 10 sieve and potentially leads to over-conservative designs. However, ER imaging provides a two-dimensional (2D) profile of bulk ER of backfill material, thereby yielding more information regarding backfill uniformity compared to traditional sampling. The objective of this study was to characterize bulk ER of in-place MSE wall backfill aggregate.
In this study, MSE walls selected by KDOT were tested using ER imaging during construction to determine bulk ER of the backfill. Variations within backfill ER may be a result of varying aggregate material, inclusions of fines, thoroughness of compaction, and the presence of water. ER imaging was used on five walls: four MSE walls and one gravity retaining wall that contained no reinforcement. One MSE wall contained metal reinforcement, while the other four walls contained geosynthetic. The ER imaging field method produced a 2D profile that depicted ER uniformity for bulk analysis. A post processing algorithm was generated to remove the subjective nature of the ER imaging results. The program determines the bulk ER based upon the ER imaging results. These results indicate that the laboratory analysis of AASHTO T 288-12 under-estimates the bulk ER of in-situ backfill material. Identification of a material’s bulk ER will help characterize the ER of aggregates in a complementary KDOT project. Results of this study will be used to recommend an in-situ test method for aggregate used by KDOT.
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Effet de la végétation sur la variabilité de la profondeur de dégel à petite échelle dans un paysage de tourbières en forêt boréale dans les Territoires du Nord-OuestHiggins, Kellina Leslie 08 1900 (has links)
Afin de mieux comprendre les effets des changements climatiques sur le pergélisol, il s’avère essentiel d’obtenir une meilleure connaissance des facteurs physiques et biologiques l’influençant. Même si plusieurs études font référence à l’influence de la végétation sur le pergélisol à grande échelle, l’effet de la végétation sur la profondeur du front de dégel du pergélisol à l’échelle de mètres, tel qu’exploré ici, est peu connu. L’étude s’est effectuée dans une forêt boréale tourbeuse dans la zone à pergélisol discontinu au sud des Territoires du Nord-Ouest (N61°18’, O121°18’). Nous avons comparé la profondeur de dégel aux mesures du couvert végétal suivantes : densité arborescente, couvert arbustif, indice de surface foliaire et présence de cryptogames (lichens et bryophytes). Nous avons trouvé qu’une plus grande densité arborescente menait à une moins grande profondeur de dégel tandis que le couvert arbustif (<50cm de hauteur) n’avait aucune influence. De plus, la profondeur de dégel dépendait de l’espèce des cryptogames et des microformes. Cette recherche quantifie l’influence de la végétation par strate sur la dégradation du pergélisol. Ultimement, les résultats pourront être pris en considération dans la mise en place des modèles, afin de valider les paramètres concernant la végétation, la dégradation du pergélisol et le flux du carbone. / In order to better understand the impacts of climate change on permafrost degradation, it is important to understand the influence of abiotic and biotic factors on permafrost dynamics. While studies allude to the effect of broad vegetation groups on permafrost dynamics at landscape-scale, the role vegetation plays in affecting the spatial variability of active-layer development on the scale of metres, as explored here, is largely unknown. The study was carried out in a boreal forest-peatland landscape in the discontinuous permafrost zone in the southern Northwest Territories (N61°18’, W121°18’). We examined the influence of the following vegetation characteristics on the spatial variability of thaw depth: tree density, shrub cover, leaf area index, and cryptogam presence (lichen and bryophyte). We found that greater tree density was associated with shallower thaw depths while shrub cover (<50cm height) had a negligible influence. Furthermore, thaw depth depended on the cryptogam species cover and microform. This research quantifies the impact of vegetation by strata on thaw depth and may ultimately serve to refine vegetation parameters in ecosystem models and land surface schemes as part of climate models.
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An Investigation of the ca. 2.7 Ga Late Archean Magmatic Event (LAME) in the Superior Province using 1-D Thermal ModellingAhmad, Seema 03 March 2010 (has links)
The Late Archean Magmatic Event (LAME), ca. 2.7 Ga, was the greatest crustal addition event in Earth history. My focus is the Superior Province of Canada, where LAME occurred ca. 2.75 – 2.65 Ga. Mantle plumes impinged on the Abitibi subprovince, where ~ 16 km regional thickness of tonalite-trondhjemite-granodiorite (TTG) melt was produced. Granites (sensu stricto) were the last magmatic phase of LAME, with a Superior-wide regional thickness of ~ 1 – 3 km.
Assuming a crustal source for both TTG and granites, I use 1-D thermal models to investigate the origin of TTG in the Abitibi subprovince and that of late granites in the Superior Province. Melting curves appropriate to the source of TTG and granites are used to determine the thickness of melt produced in the models.
I show that the incorporation of upward melt transfer into a standard model of lower crustal melting may increase the amount of predicted melt by ~ 1/(1-f), where f denotes the fraction of melt that is on average being extracted from the source rocks. Partitioning of heat producing elements between melt and restite reduces the amount of melt produced, but the effect is secondary compared to the increase in melt production through upward melt transfer.
For the Abitibi subprovince, I show that the emplacement of a single plume coupled with the emplacement of a 12-km-thick greenstone cover can generate a maximum of ~ 9-km-thickness of TTG melt. However, the emplacement of a series of plumes, each coupled with the emplacement of a 3-km-thick greenstone cover and a 10-km-thick sill results in ~ 20-km-thickness of TTG melt. My model incorporates delamination of restitic eclogite.
Finally, I show that late granites in the Superior Province may have resulted from thickening of a crust that had been “pre-heated” during earlier arc activity and that prolonged granitic magmatism observed in some areas of the Superior Province may be explained by late underthrusting of fertile source rocks into deeper and hotter regions of the crust.
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An Investigation of the ca. 2.7 Ga Late Archean Magmatic Event (LAME) in the Superior Province using 1-D Thermal ModellingAhmad, Seema 03 March 2010 (has links)
The Late Archean Magmatic Event (LAME), ca. 2.7 Ga, was the greatest crustal addition event in Earth history. My focus is the Superior Province of Canada, where LAME occurred ca. 2.75 – 2.65 Ga. Mantle plumes impinged on the Abitibi subprovince, where ~ 16 km regional thickness of tonalite-trondhjemite-granodiorite (TTG) melt was produced. Granites (sensu stricto) were the last magmatic phase of LAME, with a Superior-wide regional thickness of ~ 1 – 3 km.
Assuming a crustal source for both TTG and granites, I use 1-D thermal models to investigate the origin of TTG in the Abitibi subprovince and that of late granites in the Superior Province. Melting curves appropriate to the source of TTG and granites are used to determine the thickness of melt produced in the models.
I show that the incorporation of upward melt transfer into a standard model of lower crustal melting may increase the amount of predicted melt by ~ 1/(1-f), where f denotes the fraction of melt that is on average being extracted from the source rocks. Partitioning of heat producing elements between melt and restite reduces the amount of melt produced, but the effect is secondary compared to the increase in melt production through upward melt transfer.
For the Abitibi subprovince, I show that the emplacement of a single plume coupled with the emplacement of a 12-km-thick greenstone cover can generate a maximum of ~ 9-km-thickness of TTG melt. However, the emplacement of a series of plumes, each coupled with the emplacement of a 3-km-thick greenstone cover and a 10-km-thick sill results in ~ 20-km-thickness of TTG melt. My model incorporates delamination of restitic eclogite.
Finally, I show that late granites in the Superior Province may have resulted from thickening of a crust that had been “pre-heated” during earlier arc activity and that prolonged granitic magmatism observed in some areas of the Superior Province may be explained by late underthrusting of fertile source rocks into deeper and hotter regions of the crust.
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Temporal Variations in the Compliance of Gas Hydrate FormationsRoach, Lisa Aretha Nyala 20 March 2014 (has links)
Seafloor compliance is a non-intrusive geophysical method sensitive to the shear modulus of the sediments below the seafloor. A compliance analysis requires the computation of the frequency dependent transfer function between the vertical stress, produced at the seafloor by the ultra low frequency passive source-infra-gravity waves, and the resulting displacement, related to velocity through the frequency. The displacement of the ocean floor is dependent on the elastic structure of the sediments and the compliance function is tuned to different depths, i.e., a change in the elastic parameters at a given depth is sensed by the compliance function at a particular frequency. In a gas hydrate system, the magnitude of the stiffness is a measure of the quantity of gas hydrates present. Gas hydrates contain immense stores of greenhouse gases making them relevant to climate change science, and represent an important potential alternative source of energy. Bullseye Vent is a gas hydrate system located in an area that has been intensively studied for over 2 decades and research results suggest that this system is evolving over time.
A partnership with NEPTUNE Canada allowed for the investigation of this possible evolution. This thesis describes a compliance experiment configured for NEPTUNE Canada’s seafloor observatory and its failure. It also describes the use of 203 days of simultaneously logged pressure and velocity time-series data, measured by a Scripps differential pressure gauge, and a Güralp CMG-1T broadband seismometer on NEPTUNE Canada’s seismic station, respectively, to evaluate variations in sediment stiffness near Bullseye. The evaluation resulted in a (- 4.49 x10-3± 3.52 x 10-3) % change of the transfer function of 3rd October, 2010 and represents a 2.88% decrease in the stiffness of the sediments over the period. This thesis also outlines a new algorithm for calculating the static compliance of isotropic layered sediments.
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Temporal Variations in the Compliance of Gas Hydrate FormationsRoach, Lisa Aretha Nyala 20 March 2014 (has links)
Seafloor compliance is a non-intrusive geophysical method sensitive to the shear modulus of the sediments below the seafloor. A compliance analysis requires the computation of the frequency dependent transfer function between the vertical stress, produced at the seafloor by the ultra low frequency passive source-infra-gravity waves, and the resulting displacement, related to velocity through the frequency. The displacement of the ocean floor is dependent on the elastic structure of the sediments and the compliance function is tuned to different depths, i.e., a change in the elastic parameters at a given depth is sensed by the compliance function at a particular frequency. In a gas hydrate system, the magnitude of the stiffness is a measure of the quantity of gas hydrates present. Gas hydrates contain immense stores of greenhouse gases making them relevant to climate change science, and represent an important potential alternative source of energy. Bullseye Vent is a gas hydrate system located in an area that has been intensively studied for over 2 decades and research results suggest that this system is evolving over time.
A partnership with NEPTUNE Canada allowed for the investigation of this possible evolution. This thesis describes a compliance experiment configured for NEPTUNE Canada’s seafloor observatory and its failure. It also describes the use of 203 days of simultaneously logged pressure and velocity time-series data, measured by a Scripps differential pressure gauge, and a Güralp CMG-1T broadband seismometer on NEPTUNE Canada’s seismic station, respectively, to evaluate variations in sediment stiffness near Bullseye. The evaluation resulted in a (- 4.49 x10-3± 3.52 x 10-3) % change of the transfer function of 3rd October, 2010 and represents a 2.88% decrease in the stiffness of the sediments over the period. This thesis also outlines a new algorithm for calculating the static compliance of isotropic layered sediments.
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