Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item PARAMETRIC STUDY OF SOIL DRYING IN THE FIELD FOR COMPACTION QUALITY ASSURANCE(2017) Afsharikia, Zahra; Schwartz, charles W.; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Moving towards modulus based methods of soil compaction quality assurance using lightweight deflectometers (LWD) requires evaluation of the LWD measured modulus in the field. The resilient modulus of geomaterials is not only influenced by the moisture content (MC) at the time of compaction, but also by the MC at the time of testing, which may be up to few hours after compaction. A parametric study was performed using SoilVision’s SVFlux analysis package to model the variation of soil moisture profile with depth versus time as a function of environmental factors. Then the drying in a compacted soil layer was modeled and compared to the volumetric water content measurements in an instrumented large-scale test pit. Finally, LWD modulus values in the field were captured immediately and a few hours after compaction to exhibit the variation of modulus with time and to identify if the stiffness gain in geomaterial is significant.Item Induced Soil Liquefaction for the Freeing of Grounded Ships(2017) Cerquetti, Jeffrey; Aggour, Mohamed S.; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The objective of this study is to determine the feasibility of freeing a grounded ship by liquefying the surrounding soils. Ships either moored or traveling in near-shore waters and subjected to storm events, will experience waves energetic enough to direct the ship toward the shore. The ship can then become embedded in the soils (grounded) close to the shore. The study included two phases. Phase one was an experimental study where models of three ship sections representing standard classes of ships were constructed. These models were embedded in a saturated sand in an especially constructed tank. Pull tests were done initially to establish benchmark freeing forces and then air blasts were used to produce the dynamic force needed to liquefy the surrounding soils. The models subsequently regained buoyancy. The second phase of the study utilized the data obtained from the testing program to extrapolate those data to a response of an actual-size ship. The conclusion showed that ships grounded can be freed by liquefaction of the surrounding soils. This novel technique of restoring a ship’s buoyancy and thus refloating it was demonstrated experimentally on model ships and analytically by determining the air pressure needed to free an actual ship in a grounding event. This new technique will have an economical value for the shipping industry and could provide an environmentally safe approach in dealing with grounded ships.Item Evolution of strength and physical properties of ultramafic and carbonate rocks under hydrothermal conditions(2016) Lisabeth, Harrison; Zhu, Wenlu; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Interaction of rocks with fluids can significantly change mineral assemblage and structure. This so-called hydrothermal alteration is ubiquitous in the Earth’s crust. Though the behavior of hydrothermally altered rocks can have planet-scale consequences, such as facilitating oceanic spreading along slow ridge segments and recycling volatiles into the mantle at subduction zones, the mechanisms involved in the hydrothermal alteration are often microscopic. Fluid-rock interactions take place where the fluid and rock meet. Fluid distribution, flux rate and reactive surface area control the efficiency and extent of hydrothermal alteration. Fluid-rock interactions, such as dissolution, precipitation and fluid mediated fracture and frictional sliding lead to changes in porosity and pore structure that feed back into the hydraulic and mechanical behavior of the bulk rock. Examining the nature of this highly coupled system involves coordinating observations of the mineralogy and structure of naturally altered rocks and laboratory investigation of the fine scale mechanisms of transformation under controlled conditions. In this study, I focus on fluid-rock interactions involving two common lithologies, carbonates and ultramafics, in order to elucidate the coupling between mechanical, hydraulic and chemical processes in these rocks. I perform constant strain-rate triaxial deformation and constant-stress creep tests on several suites of samples while monitoring the evolution of sample strain, permeability and physical properties. Subsequent microstructures are analyzed using optical and scanning electron microscopy. This work yields laboratory-based constraints on the extent and mechanisms of water weakening in carbonates and carbonation reactions in ultramafic rocks. I find that inundation with pore fluid thereby reducing permeability. This effect is sensitive to pore fluid saturation with respect to calcium carbonate. Fluid inundation weakens dunites as well. The addition of carbon dioxide to pore fluid enhances compaction and partial recovery of strength compared to pure water samples. Enhanced compaction in CO2-rich fluid samples is not accompanied by enhanced permeability reduction. Analysis of sample microstructures indicates that precipitation of carbonates along fracture surfaces is responsible for the partial restrengthening and channelized dissolution of olivine is responsible for permeability maintenance.