This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Thesis: Ph. D., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2019 / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (pages 237-251). / Quantifying chemical fluxes between natural waters and their benthic sediments is a central problem in biogeochemistry, yet it is notoriously challenging. A relatively new method for measuring benthic fluxes, Eddy Correlation (EC) addresses many shortcomings of traditional techniques. Minimally invasive and measured in situ, EC is based on high-speed, simultaneous, and co-located velocity and concentration measurements. It has been successfully used in a range of settings to determine benthic fluxes of dissolved oxygen, using an Acoustic Doppler Velocimeter (ADV) to measure water velocity and an oxygen microelectrode to measure concentration. Widespread application to a larger range of compounds is limited, however, by the lack of chemical sensors that are fast, small, and sensitive enough for EC. To address this need, a novel trimodal sensor has been developed that is capable of high-speed, high-resolution measurements of fluorescence, temperature, and conductivity. / The core of the instrument is an optical fiber spectrofluorometer, which utilizes an LED for low-cost excitation; pair of 1000 [mu]m optical fibers for minimal disruption to velocity measurements; a tunable monochromator to enable a wide range of detection wavelengths; and a custom photon counting detector for maximum sensitivity. It can be used in an EC system to measure benthic fluxes of fluorescing compounds, such as fluorescent dissolved organic material. A fast thermistor and conductivity cell are also located at the tips of the optical fibers, enabling heat and salinity flux measurements that can be used as tracers for submarine groundwater discharge. Additionally, the ability to measure three simultaneous fluxes enables exploration of the potential to use the measured flux of one compound to infer another. Such 'flux tracing' would vastly expand the range of chemicals measurable with EC. / After development and testing of the individual sensors, the ability of the instrument to take three simultaneous, co-located measurements was demonstrated in a flume: under turbulent flow, the three sensors were able to detect similar features from an injection of warm, salty, fluorescent dye. The instrument was then coupled to an ADV for flux measurements, and tested in a specially constructed laboratory tank whereby benthic fluxes were released at known rates from the tank floor. The fluxes measured by all three sensors compared favorably with expected values. In addition, fluxes measured by the three sensors were observed to track each other, demonstrating the viability of flux tracing in settings with co-transported compounds. / by Irene Helen Hu. / Ph. D. / Ph.D. Massachusetts Institute of Technology, Department of Civil and Environmental Engineering

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2019 / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 118-125). / Estimates suggest that the world needs a 50% increase in food production to meet the demands of the 2050 global population (Tilman et. al. 2011). Cropland expansion is unlikely to be sufficient, and yield improvements that require more inputs may lead to more environmental damage. This work focuses on reallocating limited land and water resources to optimize cropping patterns. By combining optimization methods, surrogate modeling, global data sources, data assimilation, and hydrologic modeling, we identify opportunities for increasing food-crop production and cash-crop revenue, while maintaining sustainability constraints that limit cropland expansion and prevent groundwater depletion. We apply the framework in India's Krishna river basin and find that reallocating resources to meet or exceed current production can lead to 96% gain in net revenue as resources over an estimated current baseline. Resources in this case are moved to high-yielding cash crops. Imposing a self-sufficient southern diet which depends on rice reduces the gains to 77% while imposing a self-sufficient national diet with more emphasis on wheat eliminates all net revenue gains to the region. The approach described in this thesis, highlights the trade-offs between food production, cost and environmental impacts in achieving specified food-security objectives. This research contributes to the field in two ways: 1) it provides a novel method for combining remotely sensed data, surrogate models and optimization to understand agricultural trade-offs, and 2) it furthers the discussion on food and water security and sustainable resource management by demonstrating that resource reallocation with sustainability constraints provides revenue gains in certain situations. / by Anjuli Jain Figueroa. / Ph. D. / Ph.D. Massachusetts Institute of Technology, Department of Civil and Environmental Engineering

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2019 / Cataloged from PDF version of thesis. / Includes bibliographical references. / Submerged outfalls consisting of multiple, closely spaced jets are often used to discharge industrial effluents in coastal waterbodies. Examples of such effluents include heated water from thermal power plants, treated wastewater effluent from sewage treatment plants, and reject brine from desalination plants. At locations with shallow water depth, the interaction between adjacent jets is enhanced and can affect mixing. The mixing of submerged outfalls in shallow water is studied in this thesis with particular emphasis on discharge of dense treated brine from desalination plants. Treatment options for brine involve blending it with less saline effluents or its concentration, and can have significant effect on the design of outfall and its mixing. The effect of shallow water depth on dilution of submerged outfalls is determined first for quiescent conditions, and a unified theory is developed for single and multiple jets discharging in shallow water. / The effect of shallowness is shown to be characterized by a non-dimensional parameter, which depends on the receiving water depth and the effluent momentum and buoyancy fluxes. The effect of brine treatment processes, which affect both discharge momentum and buoyancy, on the dilution of various contaminants is determined next. The effect of brine treatment on outfall design is also explored, and optimum outfall design variables are calculated for a range of conditions. In the presence of a crossflow, the mixing dynamics of multiple port outfalls are quite different, and can give rise to complex jet interactions and even reversing flow close to the upstream jets. Laboratory experiments, in which discharge and ambient parameters are varied, have led to an improved empirical expression for dilution. In addition to the strength of crossflow, outfall length and spacing of jets are also found to significantly affect dilution. / A numerical model, capable of modeling the discharge of multiple jets in a crossflow, is developed and shows significant improvement over existing models. / by Ishita Shrivastava. / Ph. D. / Ph.D. Massachusetts Institute of Technology, Department of Civil and Environmental Engineering

Thesis: Ph. D. in the field of Geotechnical and Geoenvironmental Engineering, Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2019 / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 165-168). / Overpressure or fluid pressure in excess of hydrostatic pressure has been observed globally in many deep water sedimentary basins. One of the possible mechanisms for overpressure is the smectite-to-illite (S-I) transformation. During the transformation, the basal spacing of the smectite layer reduces. The interlayer water is released into pore space, causing an increase in pore pressure. This thesis investigates the compression and permeability behavior change due to S-I transformation. Uniaxial compression testing was performed on smectitic and illitic mudrocks. The original Gulf of Mexico - Eugene Island (GoM-EI) mudrock sets the baseline for smectitic mudrock in order to compare with illitic mudrocks. Two methods were used to create illitic mudrock from the GoM-EI sediment. / The illitic mudrock A was cooked in a high temperature constant rate of strain (CRS) device with effective stress applied (200 °C and 30 days); the illitic mudrock B was cooked in a hydrothermal cooker in a slurry state (250 °C and 18 days). The multi-functional high temperature CRS device was designed from scratch to tackle the challenge of measuring the mechanical properties of a mudrock and transforming the clay minerals. Although the methods of inducing S-I transformation are different, similar degrees of illitization for the illitic mudrock A and B was achieved by selecting the right temperature and time combination. The mineral transformation does not greatly alter the compressibility of the mudrocks. However, both the illitic mudrock A and B sit higher in porosity space than the smectitic mudrock at low stress level. / As effective stress increases, the illitic mudrock A converges with the smectitic mudrock, while the illitic mudrock B reverses order with the smectitic mudrock at 30 MPa. The permeability of the smectitic mudrock ranges over five orders from 10⁻¹⁶ to 10⁻²⁰ m² from a porosity of 0.58 to 0.23. The permeability of the mudrocks are greatly increased by the mineral transformation. The permeability ratio of the illitic mudrocks over the smectitic mudrock increases from 2 to 12 as porosity decreases. The creep rate (C[subscript alpha]) at room temperature and elevated temperature were measured during the transformation stage of the illitic mudrock A. C[subscript alpha] at elevated temperature increases by 50 % compared with that at room temperature. The increase in rate is caused by mineral transformation. Using the difference in rate, a model is proposed to estimate the effective stress reduction or overpressure generation based on the degree of mineral transformation. / by Chunwei Ge. / Ph. D. in the field of Geotechnical and Geoenvironmental Engineering / Ph.D.inthefieldofGeotechnicalandGeoenvironmentalEngineering Massachusetts Institute of Technology, Department of Civil and Environmental Engineering

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 1999. / Includes bibliographical references (leaves 107-111). / by Li Yu. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2017 / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 178-190). / The Nile basin is an ecosystem under stress due to rapid population growth, urgent needs for more efficient utilization of natural resources, potential impacts of climate change, and persistent conflicts between riparian countries on the limited set of resources. This thesis develops a framework for optimal allocation of land and water resources to agriculture and hydropower production in the upper Blue Nile (UBN) basin, which contributes about 60 percent of the Nile river flow. The framework consists of three optimization models that aim to: (a) provide accurate estimates of the basin water budget components, (b) allocate land and water resources optimally to rain-fed, and irrigated agriculture, and (c) allocate water to agriculture and hydropower production, and investigate trade-offs between them. This thesis makes two methodological contributions. / First, a data assimilation procedure suitable for data-scarce basins is proposed to deal with data limitations and produce estimates of hydrologic components especially evaporation, consistent with the principles of mass and energy conservation while also fitting closely available observations from satellite remote sensing and ground stations. The spatial distribution of evaporation from the UBN basin is poorly known. This thesis provides new spatial maps of the monthly evaporation. Second, the most representative datasets on topography and soil properties are objectively identified, compared to other datasets, and used to delineate the arable land in the basin. Maps of suitable soils are incorporated into a land-water allocation model that allows for enhancement of the soils from one suitability class to another to increase agricultural productivity in return for an investment in soil inputs such as fertilizers. / The assimilated hydrology and the delineated arable lands are used as input to an optimization model that allocates land to rain-fed agriculture while maximizing the total net economic benefits. The same framework is extended to incorporate irrigated agriculture in the basin. Eleven proposed irrigation projects are screened, and only three of them were found economically attractive. This optimal agricultural expansion, including rain-fed and irrigated agriculture, is expected to reduce the basin flow by 7.6 cubic kilometres, impacting countries downstream from the UBN. Cooperation scenarios that limit the magnitude of this reduction are studied and their impact on the net economic benefit is quantified. The optimization framework is expanded further to include hydropower production. Optimal operation rules for the Grand Ethiopian Renaissance dam (GERD) are identified to maximize annual hydropower generation from the dam while achieving a relatively uniform monthly production rate. / Trade-offs between agricultural expansion and hydropower generation are analysed in an attempt to define scenarios for cooperation that would achieve win-win outcomes for all riparian countries of the basin. / by Mariam M. Allam. / Ph. D. / Ph.D. Massachusetts Institute of Technology, Department of Civil and Environmental Engineering

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2017 / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 399-408). / The development of constitutive models that can realistically represent the effective stress-strain-strength of the soil properties is essential for making accurate predictions using finite element analysis. Currently, most of the existing constitutive models are based on the framework of incrementally-linearized elasto-plasticity. However, most of these models do not typically consider energy conservation and are also phenomenological. This means that they can only be used to predict the behavior/ loading conditions for which they have been developed and that they often employ artificial mathematical formulations. This research proposes an improved constitutive model for sands based on the framework of Granular Solid Hydrodynamics [GSHJ. The GSH framework considers energy and momentum conservation simultaneously and, by combining them with thermodynamic considerations, develops constitutive relations for a given energy expression. / This thesis offers a detailed study of the element level behavior of the Tsinghua-Thermosoil model [TTSI (Zhang and Cheng, 2016) based on the GSH. Through this study, we identify and propose a series of modifications to the original formulation in order to improve predictions of well-established soil behavior. The proposed formulation, MIT-GH, introduces a new expression of the free energy and modifies the evolution laws and the steady state values for the internal variables. The model can successfully predict phenomena such as a unique compression response at high confining pressures (Limiting Compression Curve [LCC]) and at large shear strain conditions (Critical State Line [CSL]), and a State Boundary Surface [SBS] that limits the peak shear resistance measured in drained shear tests. The LCC and CSL conditions are defined solely from the evolution of elastic strains while the SBS is defined from the free energy expression. / Finally, our work also offers a novel use of the "double" failure mechanism -- inherent in the GSH framework. Using these mechanisms, MIT-GH can model not only Critical State conditions but also localization phenomena. The proposed criterion for the localization is the maximum expected peak friction angle that a specimen can develop at different void ratios and stress levels. This study also includes a detailed parametric analysis of the model and a proposal for the calibration of the model. The proposed MIT-GH model should be considered as a first generation formulation based on the principles of granular solid hydrodynamics and how it ties to classic knowledge of soil behavior and prior elasto-plastic models. Further research is now needed to extend the framework to address more complex features of sand behavior including the cyclic response and liquefaction. / by Andriani-loanna Panagiotidou. / Ph. D. / Ph.D. Massachusetts Institute of Technology, Department of Civil and Environmental Engineering

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2005. / Includes bibliographical references (leaves 211-235). / (cont.) characterization, and kink criterion implementation, form a synergistic analysis of the mechanistic debonding behavior affected by moisture. Results have shown that moisture affected debonding is a highly complex phenomenon that involves physical changes in the bond as well as in its constituent materials. In particular, moisture can initially enhance or reduce the interface fracture toughness, depending on the epoxy formulation being used. The toughness can, however, decrease by as much as 60% and become asymptotic upon reaching a certain moisture concentration threshold, which can be attained in as short as 2 weeks in case of peel fracture. While various debonding modes have been observed for dry specimens, epoxy/concrete interface separation, which has generally been considered an unlikely debonding mode, is observed consistently in all wet fracture specimens. Interface fracture analysis indicates that this newly discovered interfacial debonding mode is attributed to various interfacial material toughening or weakening mechanisms, and has also hinted on the possible interphase formation as a consequence of moisture diffusion. The new knowledge and results obtained from this research provide a basis for further analysis directions and for design of FRP bonded concrete systems against moisture affected debonding. / The objective of this research is to develop new mechanistic understanding of moisture affected debonding failures in carbon fiber-reinforced plastic (FRP) bonded concrete systems by means of an interface fracture approach. Central to the investigation is the use of interface fracture toughness as the quantification parameter, which is considered a bond property, to analyze, compare, and correlate physical observations of FRP bonded concrete joints. Owing to the non-negligible epoxy bond line thickness found in real-world retrofitted systems, a new tri-layer fracture energy model is derived to facilitate the computation of interface fracture toughness values. Also, with this model, the five possible debonding scenarios in FRP bonded concrete that include interface separation and material decohesion, are quantitatively distinguished and precisely described for the first time. Debonding characterization is conducted using mesoscale peel and shear fracture models manufactured with full-scale bond lines. These models are subjected to accelerated moisture conditioning to achieve various levels of moisture content in the bond region. They are then mechanically tested at selected time intervals for capturing the change in bond property and debonding mode with respect to increasing moisture concentration, which is evaluated by means of 3-dimensional moisture diffusion simulations. Diffusion and mechanical properties of the constituent materials with respect to moisture uptake are physically determined to act as inputs in the diffusion simulation and in the computation of toughness values. The knowledge of computed toughness values, simulated diffusion behavior, and observed debonding modes, combined with finite element fracture computation, mode-mix / by Ching Au. / Sc.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, February 1999. / Includes bibliographical references (leaves 73-75). / by Coach K. Wei. / S.M.

Massachusetts Institute of Technology. Dept. of Civil Engineering. Thesis. 1966. M.S. / MICROFICHE COPY ALSO AVAILABLE IN BARKER ENGINEERING LIBRARY. / Bibliography: leaves 36-38. / M.S.