M.S. - Civil and Environmental Engineering

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    Numerical Load Testing of a Geosynthetic Reinforced Soil
    ([Honolulu] : [University of Hawaii at Manoa], [December 2016], 2016-12) Kaya, Landon
    Geosynthetic reinforced soil (GRS) abutments have been increasingly used due to several advantages over traditional concrete abutment walls. Two notable advantages include: (1) Fast and cost-efficient method of construction due to the elimination of cast-in-place reinforced concrete abutments; and (2) Reduced carbon footprint due to less use of cement since cement production produces an enormous amount of carbon dioxide. GRS abutments have to be designed for settlement and bearing capacity. Available design procedures are often based on large scale load tests on GRS columns which is expensive and not routinely performed. Therefore, using a numerical model to simulate these load or performance tests would offer a more economical alternative. The FEMtij program was used for analyzing GRS load tests in 2-D and 3-D. In 2-D , the ideal constitutive models for the soil, CMU blocks, geotextile, and footing were the subloading tij, Drucker-Prager, linear elastic with post-yield softening, and linear elastic, respectively. Three factors that greatly affect the GRS capacity were investigated by performing a sensitivity analysis. These factors were the effects of soil-footing friction angle, the constitutive model of the CMU (Drucker Prager vs linear elastic), and the constitutive model of the geotextile (linear elastic with post-yield softening vs linear elastic). The 3D analyses were less successful, details of which can be found in the thesis. From the calculated 2D load-settlement and lateral displacement curves, and heat maps of shear strain, the following observations and conclusions were made: (1) The capacity of the GRS increased with increasing soil-footing friction angle. (2) Using a Drucker-Prager model for the CMUs caused the GRS to have a smaller capacity than if they were linear elastic. (3) Modelling CMU blocks with an elasto-plastic model is important due to some of the CMUs crushing during the performance tests. (4) By allowing the geotextiles to soften after exceeding its tensile strength, the GRS capacity was less than if the geotextiles were linear elastic. (5) It is important to model a softening geotextile because of the observed ripping of the geotextiles during the performance tests. (6) Shear bands were observed in the GRS columns. They are inclined at 45° and 50° to the horizontal for GRS columns without and with CMU blocks, respectively.
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    Design Guidelines for Impact Mechanical Frequency Up- Conversion Piezoelectric Energy Harvesters
    ([Honolulu] : [University of Hawaii at Manoa], [December 2016], 2016-12) Corr, Lawrence
    Vibration energy harvesters based on the impact mechanical frequency up-conversion technique utilize an impactor, which gains kinetic energy from low frequency ambient environmental vibrations, to excite high frequency systems tuned to efficiently convert mechanical energy to electrical energy. In order to design energy harvesters to take full advantage of the impact mechanical frequency up-conversion technique, it is prudent to understand the mechanisms of energy transfer from the low frequency excitations, to the impactor, and finally to the high frequency systems. The purpose of this work is to develop design guidelines for impact mechanical frequency up-conversion piezoelectric energy harvesters. The specific objectives are to develop guidelines for: • Maximum energy transfer from the impactor to high frequency system • High frequency system design to maximize energy generation from piezoelectric device • Impactor size and placement of high frequency system to maximize impactor / high frequency system interaction for a given excitation spectrum
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    Unconfined Compression Tests on Basalt Rocks from Hawaii
    ([Honolulu] : [University of Hawaii at Manoa], [May 2016], 2016-05) Yamada, Miles
    Unconfined compression tests were performed on 66 basalt samples to obtain index properties and elastic constants. The samples were obtained from a boring drilled at the University of Hawaii at Manoa. These values were compared to results obtained from other studies to determine correlations and observe vertical trends at the site. Properties obtained from nondestructive tests on the basalt rocks included unit weight (oven-dried, saturated-surface-dry, and apparent), unit weight through the use of a CoreLok machine, absorption, RQD, and percent recovered. Properties obtained from compression tests included unconfined compressive strength, Young’s Modulus, axial strain at failure or at 50% of ultimate load, failure type, and failure plane angle to horizontal. The results indicate that there appears to be two different layers of rock at the location of the boring. There is an upper layer of rock characterized by lower unit weights, higher absorption and lower strength and stiffness, compared to the lower layer of rock. This points to significantly different rock types, probably from different lava flows with somewhat different original magma composition and viscosity. It is worth noting that RQD, percent recovery and axial strain do not show discernible distinctions between these two rock units and thus appear to be less useful as indicators of distinct rock units, at least as encountered at the site. Strong correlations were observed between absorption and unit weight, as expected. Strong correlations were also noted between the various unit weights and the results of the unconfined compression tests. In particular, there are reasonably strong correlations between index properties in terms of unit weight and absorption, and test results in terms of unconfined compression strength and stiffness. No discernible correspondence was observed between field parameters in terms of RQD, percent recovery or axial strain versus index parameters and strength test results.
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    Evaluation of GSSHA for Simulating Sediment Concentrations in Steep Hawaiian Watersheds
    ([Honolulu] : [University of Hawaii at Manoa], [May 2016], 2016-05) Nielson, Jeffrey
    Physics-based hydrological models, like GSSHA, potentially have an accuracy advantage over empirical or semi-empirical models, when simulating processes in steep Hawaiian watersheds, which can be very dissimilar to lands (or field plot experiments) where the empirical relationships were developed. GSSHA, therefore, could potentially be a valuable tool for hydrology projects in Hawaii, but is seldom used in Hawaii. In this study, GSSHA was evaluated and used to predict streamflow and sediment concentrations in the upper region of Halawa watershed on leeward Oahu—a watershed with an average overland basin slope of 0.65—during single-event storms. Single-event simulations were the focus here, because of the importance of single-event storms to Hawaii’s sediment issues (other studies claim that a large portion of annual sediment flux occurs during low-frequency, high-magnitude storms). Streamflow and sediment concentration data collected at 15-minute intervals were used to calibrate and validate the simulations. Several case studies were developed to test findings from past studies, including the finding that GSSHA tends to over predict sediment for low-frequency, high-magnitude storms, when calibrated with only high-frequency, low-magnitude storms (as stated in the GSSHA manual). It was found that GSSHA becomes less accurate in sediment concentration predictions for low-frequency storms (>2-year recurrence interval) when calibrated with only high-frequency storms (<2-year recurrence interval). It is shown that the degradation in accuracy was likely a result of over prediction in streamflow. It was also found that GSSHA made more accurate predictions of streamflow when the validation storm events were similar to calibration events in rainfall duration, accumulation, and peak intensity, indicating that one set of calibration parameters may not be sufficient for all storm events. Distinctively, however, it is shown that one set of calibration parameters may be sufficient for all storm events for predicting sediment concentrations. GSSHA predicted sediment load with an 8.8% error for a validation storm six times larger (based on streamflow) than calibration. Additionally, in response to studies that have shown that many sediment transport equations over predict sediment flux in steep terrain by orders of magnitude, two sediment transport equations—Engelund-Hansen and Kilinc-Richardson—were tested and compared to determine which equation is better for steep terrain. It was found that the Engelund-Hansen equation consistently outperformed the Kilinc-Richardson equation, indicating that the Engelund-Hansen equation is a better choice for use in steep Hawaiian watersheds.
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    Designing High Performance Geopolymer Concrete Using Fly Ash and Slag
    ([Honolulu] : [University of Hawaii at Manoa], [August 2015], 2015-08) Li, Yanping
    A fly ash-based geoploymer was studied as a potential alternative to traditional Portland cement since fly ash has significantly lower CO2 contribution than traditional cement production. The fly ash-based geopolymer was developed using fly ash, slag, and alkali solution, which when combined with aggregate produces a material that has high compressive strength, acceptable workability, and suitable setting time. The compressive strength and setting time of fly ash-based geopolymer paste/mortar were studied by varying the components of the alkali solution, slag replacement content, curing temperature, and liquid to binder ratio (L/B). The workability of the geopolymer paste/mortar was examined by introducing water and super plasticizer. The compressive strength development and cracking phenomenon of the geopolymer concrete were investigated by changing the L/B ratios and curing methods. The microstructural and mineralogical characteristics of geopolymer mortars were characterized using scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), and Raman spectroscopy. Due to the complex reactions involved in geopolymer formation, hydroxide concentration and slag replacement percentage on setting time, 7-day and 28-day compressive strength. The results revealed that the compressive strength was dramatically enhanced by introducing slag into the fly ash-based geopolymer due to the formation of C-S-H and a large amount of geopolymer gel. In addition, the compressive strength was controlled by the [OH-] and [Si] concentrations of alkali solution. OH- accelerated the dissolution of glass, while silicate had a more complex role of maintaining the balance of species in solution. Elevated curing temperature resulted in higher compressive strength than room temperature. Higher compressive strength was obtained by using lower L/B ratio. The workability was controlled by L/B ratio and silicate concentration. The setting time was controlled by solution chemistry and slag content. The formation of C-S-H and geopolymer gel was confirmed using SEM/EDS and Raman spectroscopis analyses. The DOE results showed that: for setting time, [OH-], the interaction of [Si] and [OH-], and quadratic (second-order) effect of [Si] were considered significant; for 7-day compressive strength, only [Si], [GGBS/cem] and their interaction were considered significant, while [OH-] was considered not significant; for 28-day compressive strength, all factors appeared to be important.