RSS 1.0Theses (Civil and Environmental Engineering)
Recent Submissions
-
The role of tundra vegetation in the Arctic water cycleVegetation plays many roles in Arctic ecosystems, and the role of vegetation in linking the terrestrial system to the atmosphere through evapotranspiration is likely important. Through the acquisition and use of water, vegetation cycles water back to the atmosphere and modifies the local environment. Evapotranspiration is the collective term used to describe the transfer of water from vascular plants (transpiration) and non-vascular plants and surfaces (evaporation) to the atmosphere. Evapotranspiration is known to return large portions of the annual precipitation back to the atmosphere, and it is thus a major component of the terrestrial Arctic hydrologic budget. However, the relative contributions of dominant Arctic vegetation types to total evapotranspiration is unknown. This dissertation addresses the role of vegetation in the tundra water cycle in three chapters: (1) woody shrub stem water content and storage, (2) woody shrub transpiration, and (3) partitioning ecosystem evapotranspiration into major vegetation components. In Chapter 1 I present a method to continuously monitor Arctic shrub water content. The water content of three species (Salix alaxensis, Salix pulchra, Betula nana) was measured over two years to quantify seasonal patterns of stem water content. I found that spring uptake of snowmelt water and stem water storage was minimal relative to the precipitation and evapotranspiration water fluxes. In Chapter 2, I focused on water fluxes by measuring shrub transpiration at two contrasting sites in the arctic tundra of northern Alaska to provide a fundamental understanding of water and energy fluxes. The two sites contrasted moist acidic shrub tundra with a riparian tall shrub community having greater shrub density and biomass. The much greater total shrub transpiration at the riparian site reflected the 12-fold difference in leaf area between the sites. I developed a statistical model using vapor pressure deficit, net radiation, and leaf area, which explained >80% of the variation in hourly shrub transpiration. Transpiration was approximately 10% of summer evapotranspiration in the tundra shrub community and a possible majority of summer evapotranspiration in the riparian shrub community. At the tundra shrub site, the other plant species in that watershed apparently accounted for a much larger proportion of evapotranspiration than the measured shrubs. In Chapter 3, I therefore measured partitioned evapotranspiration from dominant vegetation types in a small Arctic watershed. I used weighing micro-lysimeters to isolate evapotranspiration contributions from moss, sedge tussocks, and mixed vascular plant assemblages. I found that mosses and sedge tussocks are the major constituents of overall evapotranspiration, with the mixed vascular plants making up a minor component. The potential shrub transpiration contribution to overall evapotranspiration covers a huge range and depends on leaf area. Predicted increases in shrub abundance and biomass due to climate change are likely to alter components of the Arctic hydrologic budget. The thermal and hydraulic properties of the moss and organic layer regulate energy fluxes, permafrost stability, and future hydrologic function in the Arctic tundra. Shifts in the composition and cover of mosses and vascular plants will not only alter tundra evapotranspiration dynamics, but will also affect the significant role that mosses, their thick organic layers, and vascular plants play in the thermodynamics of Arctic soils and in the resilience of permafrost.
-
Alaska Arctic coastal plain gravel pad hydrology: impacts to dismantlement removal and restoration operations ; a study on the human - hydrology relationship in Arctic environmentsTo guard against thawing permafrost and associated thaw subsidence, the oil facilities in the Arctic are constructed on gravel pads placed on top of the existing arctic tundra, however the impacts of this infrastructure to the sensitive hydrology are not fully understood. Production in some of the older fields is on the decline; however oil exploration in the Arctic Coastal Plain is resulting in the discovery and development of new reserves. In the coming years, old sites will need to be decommissioned as production transitions to new sites. New facilities will also need to be designed and constructed. Oil companies in Alaska have historically conducted operations under leases issued through the Alaska Department of Natural Resources. The leases stipulate that once resource extraction operations are completed, the facilities must be decommissioned and the sites restored, however they are often vague in their requirements and are variable in their specifics from lease to lease. As the oil companies transition to the new sites, decisions must be made regarding what should be done with vacated gravel pads. The construction of gravel pads essentially destroys underlying arctic tundra. In undisturbed areas in the Arctic, the tundra itself creates an insulating layer that limits the seasonal thaw depth to around 0.5 m. Removal of this layer causes thaw depths to greatly increase impacting the stability of the ground and the hydrology of the surrounding area. Because of this impact, other possible restoration techniques are being considered, such as vegetating and leaving the pads in place. Water movement is one of the major driving factors in the arctic contributing to permafrost degradation. Groundwater carries with it heat, which is transferred to the soil as the groundwater moves. Therefore, hydrology plays a major role in the stability of the arctic environment. This is especially relevant in areas where gravel pads exist. Gravel pads are anthropogenic structures that have significant water storage potential. Because of the unique conditions in the Arctic, pore-water flow through these gravel pads is not yet well understood. The purpose of this study is to develop a more complete scientific understanding of the driving forces behind pad pore-water movement. This study expands on fieldwork from a prior hydrological field study conducted by others. The prior study is expanded through this work by developing an associated groundwater model to the gravel pad from the field study to examine the flow through it and the controlling factors for this flow. The study site used for this project is located in Prudhoe Bay and is the pad constructed for the very first production well in Prudhoe Bay in 1968. This study demonstrates that it is the topography of the silt layer beneath the gravel pads that is the most significant factor controlling pad pore-water movement. The results from the modeling study will assist engineers and environmental scientists in better understanding the groundwater flow. This understanding will aid in the decommissioning and restoration process and help inform decision making in regards to the future of the existing pads. The results may also be used to inform the development of new infrastructure such that any new pads which are built may be constructed with their relationship to the local hydrology more in mind.
-
Establishing and testing detection methods for anti-icing and deicing chemicals using spectral dataSnow and ice accumulation on pavement reduce roadway surface friction and consequently result in diminished vehicle maneuverability, slower travel speeds, reduced roadway capacity, and increased crash risk. Though the use of chlorides and other freeze-inhibiting substances have been shown to reduce these negative factors, methods to quantify and analyze snow and ice remediation methods as well as the imposed loss of material are needed to allow state and municipal agencies to better allocate winter maintenance resources and funding. The use and application of chlorides, sand, and their related mixtures have proven to be highly effective for controlling or removing the development of ice on the roadway surface. However, if the amount of salt in solution becomes too dilute, then it no longer retains the capacity to control the development of, or to melt, ice on the roadway and may prove to be more detrimental by allowing the previously melted material to refreeze with a smoother (i.e., more slippery) surface state. The goal of this project was to determine to what extent winter roadway surfaces can be analyzed using spectrometry to determine the longevity and coverage of various types of applications. Using a systematically paired analysis of changes in spectrometric curves as solution concentrations change, relationships were generated which detected change in deicing and anti-icing compounds reliably in a lab setting. Field results were less reliable, suggesting that further comparisons and a more in-depth spectral library are needed.
-
Snowmelt hydrology in the upper Kuparuk watershed, Alaska: observations and modelingThe Fourth National Climate Assessment Report (2018) indicates that Alaska has been warming at a rate two times greater than the global average with the Arctic continuing to be experiencing higher rates of warming. Snowmelt driven runoff is the largest hydrologic event of the year in many Alaska Arctic river systems. Changes to air temperature, permafrost, and snow cover impact the timing and magnitude of snowmelt runoff. This thesis examines the variability in hydrometeorological variables associated with snowmelt to better understand the timing and magnitude of snowmelt runoff in headwater streams of Arctic Alaska. The objectives of this thesis are to: (1) use observational data to evaluate trends in air temperature, precipitation, snow accumulation, and snowmelt runoff data; (2) relate precipitation, snow cover, and air temperature to snowmelt runoff using the physically-based Snowmelt Runoff Model (SRM) to test the applicability of the model for headwater streams in the Arctic. The focus of this study is the Upper Kuparuk watershed area, located in Alaska on the north side of the Brooks Range, where several monitoring programs have operated long enough to generate a 20-year climate record, 1993-2017. Long-term air temperature, precipitation, and streamflow data collected by the University of Alaska Fairbanks at the Water and Environmental Research Center and other agencies were used for statistical analysis and modeling. While no statistically significant trends in snow accumulation and snowmelt runoff were identified during 1993-2017, observations highlight large year-to-year variability and include extreme years. Snow water equivalent ranges from 5.4 to 17.6 cm (average 11.0 cm), peak snowmelt runoff ranges from 3.84 to 50.0 cms (average 22.4 cms), and snowmelt peak occurrence date ranges from May 13 to June 5 for the Upper Kuparuk period of record. The spring of 2015 stands out as the warmest, snowiest year on record in the Upper Kuparuk. To further investigate the runoff response to snowmelt in 2015, remote sensing snow data was analyzed and recommended parameters were developed for SRM use in the Upper Kuparuk watershed. Recommended parameters were then applied to 2013 snowmelt runoff as a test year. Model results varied between the two years and provide good first-order approximation of snowmelt runoff for headwater rivers in the Alaska Arctic.
-
Pre-stress loss due to creep in precast concrete decked bulb-tee girders under cold climate conditionsThis report presents guidelines for estimating pre-stress loss in high-strength precast pretensioned concrete Decked Bulb-Tee (DBT) bridge girders in cold climate regions. The guidelines incorporate procedures yielding more accurate predictions of shrinkage and concrete creep than current 2017 American Association of State Highway and Transportation Officials (AASHTO) specifications. The results of this report will be of particular interest to researchers and cold climate bridge design engineers in improved predictions of design life and durability. The use of high-strength concrete in pre-tensioned bridge girders has increased in popularity among many state highway agencies. This fact is due to its many beneficial economic and constructability aspects. The overall cost of longer girders with increased girder spacing in a bridge that is precast with high strength concrete can be significantly reduced through the proper estimating factors. Recent research indicates that the current provisions used for calculating prestress losses in cold regions for high-strength concrete bridge girders may not provide reliable estimates. Therefore, additional research is needed to evaluate the applicability of the current provisions for estimating pre-stress losses in high-strength concrete DBT girders. Accurate estimations of pre-stress losses in design of pre-tensioned concrete girders are affected by factors such as mix design, curing, concrete strength, and service exposure conditions. The development of improved guidelines for better estimating these losses assists bridge design engineers for such girders and provide a sense of security in terms of safety and longevity. The research includes field measurements of an environmentally exposed apparatus set up to measure shrinkage, creep and strain in cylinders loaded under constant pressure for a full calendar year.
-
Numerical simulation of thermo-mechanical behavior of gypsum board wall assemblyFire safety has become a significant concern to public safety; especially in the aftermath of 9/11 attack where, according to official reports, three World Trade Center buildings collapsed because of fire. Therefore, the level of thermal insulation required from building material and structural elements has increased. In recent years, gypsum board wall assemblies have been increasingly used as compartmentation for high-rise residential and commercial buildings. The increasing popularity of gypsum board wall assemblies is due to their relatively high strength-to-weight ratio, ease of prefabrication, fast erection and good thermal insulation. Before implementation of any building material or structural element, its Fire Resistance Rating must be determined by subjecting the material or element to a standard furnace fire test. Over the years, a large database has been collected for the Fire Resistance Rating of building materials and structural elements. However, due to the expensive and time-consuming nature of the standard fire tests, determining an accurate Fire Resistance Rating can be a difficult task. In this study, the author numerically evaluated the Fire Resistance Rating of a new gypsum board wall assembly. Composite steel-EPS (Expanded Polystyrene) insulation is added to a traditional gypsum board wall assembly. The author first did numerical simulation of an experiment on the thermal response of a non-load-bearing gypsum board wall assembly to verify the thermal modeling methodology. The author then did numerical simulation of an experiment on the mechanical response of a load-bearing gypsum board wall assembly to verify the mechanical modeling methodology. Finally, the author used the verified thermal and structural modeling methodology to simulate the new composite steel-EPS gypsum board wall assembly and obtained its numerical Fire Resistance Rating. This Fire Resistance Rating should be compared with future experimental results of the new wall assembly. All modeling was done with ABAQUS V6.14.
-
2-D bed sediment transport modeling of a reach on the Sagavanirktok River, AlaskaConducting a 2-D sediment transport modeling study on the Sagavanirktok River has offered great insight to bed sediment movement. During the summer of 2017, sediment excavation of two parallel trenches began in the Sagavanirktok River, in an effort to raise the road elevation of the Dalton Highway to remediate against future floods. To predict the time in which the trenches refill with upstream sediment a 2-D numerical model was used. Three scenarios: (1) a normal cumulative volumetric flow, (2) a max discharge event, and (3) a max cumulative volumetric flow, were coupled with three sediment transport equations: Parker, Wilcock-Crowe and Meyer Peter and Müller for a total of 9 simulations. Results indicated that scenario (1) predicted the longest time to fill, ranging from 1-6 years followed by scenario (2), an even shorter time, and scenario (3) showing sustained high flows have the capability to nearly refill the trenches in one year. Because the nature of this research is predictive, limitations exist as a function of assumptions made and the numerical model. Therefore, caution should be taken in analyzing the results. However, it is important to note that this is the first time estimates have been calculated for an extraction site to be refilled on the Sagavanirktok River. Such a model could be transformed into a tool to project filling of future material sites. Ultimately, this could expedite the permitting process, eliminating the need to move to a new site by returning to a site that has been refilled from upstream sediment.
-
Near-roadway air pollution: evaluation of fine particulate matter (PM₂.₅) and ultrafine particulate matter (PM ₀.₁) in Interior AlaskaParticulate air pollution in the form of fine (PM₂.₅) and ultrafine (PM₀.₁) particles has become a global concern, especially in urban areas with high population and vehicular traffic. Considerable research has been carried out to understand the underlying processes that impact particulate pollution, but most studies have been conducted in warmer and urban regions such as in California. The Fairbanks North Star Borough (FNSB), in Interior Alaska, provides an interesting example of a relatively small- to mid-sized northern locality (population ~100,000) with persistent air quality issues and extremely cold climatic conditions for a major part of the year. Since December 2009, the FNSB has been designated a nonattainment region by the U.S. Environmental Protection Agency for the federal PM₂.₅ standard. As part of their remediation efforts, the borough and state have undertaken increased monitoring by using an on-roadway monitoring vehicle (sniffer vehicle) and stationary near-roadway sites for air quality measurements, beyond what is required for regulatory compliance. One of the goals of this project was to develop a novel data investigation and analyses methodology for the geospatial air quality data collected by the borough's mobile monitoring vehicle (years 2012-15), to shed light on the PM₂.₅ issues faced by the FNSB. In addition, this research also undertook measurements of ultrafine particle (UFP) concentration levels at four road weather information system (RWIS) sites in the FNSB region. UFPs, though unregulated, are considered to have significant human health impacts and no known studies have investigated UFPs in FNSB. In addition to UFPs, other parameters such as PM₂.₅, traffic, and weather data were measured at the same locations to investigate any underlying trends/correlations with UFPs. In the first part of the research with mobile monitoring, data were categorized in nine different groups based on their mean and standard deviation values to determine the spatiotemporal distribution of PM₂.₅. This novel way of grouping data allows identification of locations with consistently poor and consistently better air quality, by going beyond the simple analyses of means and accounting for variability and standard deviation in the data. In addition to hotspot identification, analyses found that average on-roadway PM₂.₅ concentrations were higher in North Pole (27.2 μg/m³) than in Fairbanks (12.9 μg/m³), and that average concentrations were higher in the background stationary monitoring data (29.4 μg/m³) than in the mobile monitoring data (20.0 μg/m³) for the study period. Not surprisingly, significant negative correlations (R² = 0.49 for Fairbanks, and R² = 0.31 for North Pole) were found between temperature and PM₂.₅. Temporal distribution of the data suggests that PM₂.₅ levels increase gradually in the months of October and November, peak during the months of December, January, and February, and quickly plummet beginning March. In the latter part of the study, data on UFP measurements were collected at four RWIS sites in the FNSB for four days between March 1 and 18, 2017, for five continuous hours each day. Among other parameters, PM₂.₅ concentrations, temperature, relative humidity, wind speed, and traffic volume data were collected. Data were analyzed to develop correlations between UFPs and other parameters, to compare data from this study with other studies, and to determine current roadside UFP concentration levels in interior Alaska. Fairbanks roadside locations showed higher mean UFP counts (41,700 particles/cm³) than the North Pole (22,100 particles/cm³) locations. Similarly, for the period of study, Fairbanks roadside locations showed higher PM₂.₅ concentrations and traffic counts (6.3 μg/m³; 15 vehicles/min) than the North Pole (4.6 μg/m³; 10 vehicles/min) locations, both being well below the on-roadway and background PM₂.₅ concentrations estimated in the first part of this report. Multilinear predictive models were developed for estimation of UFPs and PM₂.₅ based on weather and traffic parameters. This first study of UFPs in Alaska improves our understanding of near-roadway UFPs in cold regions.
-
An evaluation of the use of moderate resolution imaging spectroradiometer (MODIS)-derived aerosol optical depth to estimate ground level PM2.5 in AlaskaThe air quality monitoring (AQM) network in Alaska is limited to major urban areas and national parks thus leaving a large proportion of the state unmonitored. To evaluate the use of Moderate Resolution Imaging Spectroradiometer (MODIS)-derived aerosol optical depth (AOD) to predict ground-level PM2.5 concentrations and thereby increase the spatial coverage of the AQM network in Alaska, MODIS AOD was first validated against ground-based measurements of AOD in Utqiagvik and Bonanza Creek Alaska. MODIS AOD from 2000 to 2014 was obtained from MODIS collection 6 using the dark target land and ocean algorithms between the months of April and October. Based on validation results, individual Aqua and Terra products are valid for both locations at 10-kilometer and 3-kilometer resolution. In addition, combined Aqua and Terra MODIS AOD products are valid for both locations at 3-kilometer resolution and 10-kilometer resolution for Utqiagvik. The available PM2.5 data was then compared for satellite retrieval and all retrieval days to determine if there was sufficient data and the amount of bias introduced by possible low retrieval rates. Overall, Juneau had the lowest retrieval rates while Fairbanks and North Pole had the highest retrieval rates. In addition, Juneau appeared to have relatively high bias while stations located in Anchorage, Palmer, Fairbanks and North Pole had relatively low bias. Based on these findings, no models were developed for Juneau (southeast Alaska). Multilinear regression models were then developed for southcentral (Anchorage and Palmer) and interior (Fairbanks and North Pole) Alaska where the log-transform of PM2.5 was the response and meteorological data and the log-transform of MODIS AOD were the predictors. MODIS AOD appeared to be most highly correlated with PM2.5 in interior Alaska, while there was little to no correlation between MODIS AOD and PM2.5 in southcentral Alaska. All models underestimate surface PM2.5 concentrations which may be due to the high percentage of low PM2.5 values used to develop the models and the limited retrieval rates. Alternative modeling methods such as mixed-effects modeling may be necessary to develop adequate models for predicting surface PM2.5 concentrations. The MLR models did not perform well and should not be used to predict ground-based PM2.5 concentrations. Further research using alternative modeling methods should be performed. Model performance may also be improved by only using higher concentrations of PM2.5 to develop models. Overall, the limited spatial coverage of Alaska's air quality monitoring network and the low temporal resolution of MODIS-derived AOD make modeling the relationship between MODIS AOD and PM2.5 difficult in Alaska.
-
Phytoremediation strategies for recalcitrant chlorinated organicsThe purpose of the research was to investigate novel strategies for the phytoremediation of recalcitrant chlorinated organic soil contaminants. The recalcitrance of many chlorinated organics is related to chemical stability and bioavailability. Mycorrhizal fungi have the potential to enhance the degradation of such compounds through the action of lignolytic enzyme systems, and to increase the bioavailability of such compounds through increased root surface area and reach. Furthermore, the addition of surfactants has the potential to increase compound bioavailability via increased solubility. The organochlorine pesticide aldrin, and the polychlorinated biphenyl 3,3'4,4 '-tetrachlorobiphenyl (TCB) were chosen as representative recalcitrant contaminants. Feltleaf willow (Salix alaxensis) and balsain poplar (Populus balsamifera) were chosen as vegetative species likely to be useful for phytoremediation in sub-arctic ecosystems. Mixed-culture mycorrhizal fungi were first shown to be capable of taking up the hydrophobic contaminants in vitro. In the same experiments, surfactant addition increased the level of contaminant uptake. In subsequent vegetative uptake studies, mycorrhizal infection was highly correlated with the uptake of aldrin and TCB in the willow systems. In the poplar systems, this correlation was not as strong. Once taken up into the vegetative matrix of either species, most of the carbon originating from the chlorinated compounds existed as bound transformation products. Additionally, water-soluble transformation products of aldrin were formed in all of the soils tested, and such transformations were enhanced in the presence of vegetation. TCB transformation products were not detected in any of the soils tested. Surfactant addition did not impact the fate of either contaminant in the vegetative uptake studies. The surfactants, in the concentrations added, did not sufficiently solubilize the contaminants into the soil solution. The results of these studies indicated that the phytoremediation of recalcitrant chlorinated organics such as aldrin and TCB could be enhanced through the action of mycorrhizal fungi, and that surfactant addition has the potential to increase mycorrhizal uptake. Field studies were recommended, involving the use of specific degradative fungal species and effective surfactants.
-
Fatigue behavior of conventional and rubberized asphalt mixesOne of the main distress modes of flexible pavements is the fatigue cracking of the asphalt concrete surface layer. The addition of crumb-rubber modifier (CRM), obtained from scrap tires, to asphalt-aggregate mixtures has shown promise in enhancing their fatigue behavior. In this study, conventional unmodified and CRM modified asphalt-aggregate mixtures are evaluated in terms of their fatigue behavior. Controlled-strain flexural beam fatigue tests are conducted in the laboratory over a wide range of temperatures. Experimental results are compared in terms of flexural, tensile and compressive stiffnesses, phase angle, fatigue life and cumulative dissipated energy. Results showed that CRM mixes are more flexible than unmodified mixes, and that mix fatigue resistance is enhanced by the addition of CRM. Furthermore, a method of converting controlled-strain test data into equivalent controlled-stress behavior is presented. Experimental results revealed the existence of two types of controlled-strain stiffness-ratio variations. For each type of variation, an equivalent controlled-stress stiffness-ratio variation with cycles is derived. Using the predicted variations, fatigue lives for both modes of loading are determined. Predictions showed that, at a given temperature, controlled-stress mode of loading yields, as expected, shorter fatigue lives than its controlled-strain counterpart. An implicit validation of the proposed conversions revealed that fatigue equation parameters K and n for the different mixes fit within the range of values obtained from the literature for controlled-stress conditions. In addition, a fatigue life model, applicable to the haversine pattern of loading used in this study, is presented. The model takes into account the cumulative dissipated energy to failure, mode-of-loading, and initial phase angle, strain and stiffness of the mix. Analogy with the traditional strain-based fatigue equation revealed that K is a temperature-dependent parameter, whereas n and m are independent of mix temperature. A decrease in K is associated with an increase in temperature. The newly developed model is then used to predict fatigue lives of conventional and CRM mixes in typical pavement structures. For this purpose, a finite element-based mechanistic analysis is used. Results revealed the enhanced fatigue resistance of CRM mixes in comparison to unmodified conventional mixes.
-
Tests and analysis of geogrids as base-reinforcing materialsA quantitative assessment of geogrids as base reinforcing material in paved roads is clearly necessary when a design is needed and decisions are to be made as a consequence. Two full scale single wheel load tests were conducted to determine the performance of geogrids as base reinforcing materials in paved roads. These two full scale tests were set up with different base thicknesses, material properties, loading conditions and geogrids. Load, speed, and direction of a test cart were controlled with a computer. Although many types of instruments were installed, measurements of vertical deformation of the pavement surface proved to be the most useful. The Traffic Benefit Ratio (TBR), defined as the ratio of the life of a reinforced section to the life of a similar unreinforced section, was used as a primary design parameter. Comparisons between reinforced and unreinforced bases are presented. The parameters used for comparison were permanent vertical deformation, number of repetitions to failure, tire load, and thickness of base course. Test results showed that the maximum TBR for a Tensar BR2 geogrid was 10. This TBR was obtained at a design deformation of 1.0 inch with 2 inches of asphalt over 10 inches of base over a CBR 3 clay subgrade. TBR's for other conditions ranged between 1 and 10. A design reference chart is presented for using Tensar BR1 and BR2 Geogrids.
-
Fracture and shakedown of pavements under repeated traffic loadsUnder repeated external loads, engineering structures or objects may fail by large plastic deformation or fatigue. Shakedown will occur when the accumulation of plastic deformation ceases under repeated loads; the response of the system is then purely elastic. Fatigue and shakedown have been individually studied for decades and no attempt has been made to couple these two mechanisms in the mechanics analysis. In this study, an attempt is made to couple shakedown and fatigue in pavement mechanics analysis using numerical simulation. The study covers three main areas: fatigue, static shakedown, and kinematic shakedown analysis. A numerical approach to fatigue analysis is proposed based on elastic-plastic fracture mechanics. The amount of the crack growth during each load cycle is determined by using the J-integral curve and $\rm R\sb{-}curve.$ Crack propagation is simulated by shifting the $\rm R\sb{-}curve$ along the crack growth direction. Fatigue life is predicted based on numerically estabiished fatigue equation. The numerical results indicate that the algorithm can be applied to fatigue analyses of different materials. A numerical algorithm based on the finite element method coupled with the nonlinear programming is proposed in static shakedown analysis. In this algorithm, both the inequality and equality constraints are included in the pseudo-objective function. These constraints are normalized by the material yield stress and the reference load, respectively. A multidirectional search algorithm is used in the optimization process. The influence of finite element mesh on shakedown loads is investigated. An algorithm that utilizes eigen-mode to construct the arbitrary admissible plastic deformation path is proposed in kinematic shakedown analysis. This algorithm converts the shakedown theorem into a convex optimization problem and can be solved by using a multidirectional search algorithm. Fatigue behavior of a two-layer full-depth pavement system of asphalt concrete is analyzed using the proposed numerical algorithm. Fatigue crack growth rate is estimated and fatigue life is predicted for the system. Shakedown analyses are also carried out for the same pavement system. The comparison between the shakedown load and the fatigue failure load with respect to the same crack length indicates that the shakedown dominates the response of the pavement system under traffic load.
-
Modeling Biosorption Of Cadmium, Zinc And Lead Onto Native And Immobilized Citrus Peels In Batch And Fixed Bed ReactorsBiosorption, i.e., the passive uptake of pollutants (heavy metals, dyes) from aqueous phase by biosorbents, obtained cheaply from natural sources or industrial/agricultural waste, can be a cost-effective alternative to conventional metal removal methods. Conventional methods such as chemical precipitation, membrane filtration or ion exchange are not suitable to treat large volumes of dilute discharge, such as mining effluent. This study is a continuation of previous research utilizing citrus peels for metal removal in batch reactors. Since fixed bed reactors feature better mass transfer and are typically used in water or waste water treatment using ion-exchange resins, this thesis focuses on packed bed columns. A number of fixed bed experiments were conducted by varying Cd inlet concentration (5-15 mg/L), bed height (24-75 cm) and flow rate (2-15.5 ml/min). Breakthrough and saturation uptake ranged between 14-29 mg/g and 42-45 mg/g respectively. An empty bed contact time of 10 minutes was required for optimum column operation. Breakthrough curves were described by mathematical models, whereby three popular models were shown to be mathematically identical. Citrus peels were immobilized within an alginate matrix to produce uniform granules with higher uptake capacity than raw peels. All breakthrough curves of native and immobilized peels were predicted using external and intra-particle mass transfer resistances from correlations and batch experiments, respectively. Several analogous mathematical models were identified; other frequently used models were shown to be the approximate derivatives of a single parent model. To determine the influence of competing metals, batch and fixed bed experiments were conducted in different binary combinations of Pb, Cd, Zn and Ca. Equilibrium data were analyzed by applying competitive, uncompetitive and partially competitive models. In column applications, high affinity Pb replaced previously bound Zn and Cd in Pb-Zn and Pb-Cd systems, respectively. However, the Cd-Zn system did not show any overshoot. Calcium, which is weakly bound, did not affect target metal binding as much as other metals. Saturated columns were desorbed with 0.1 N nitric acid to recover the metal, achieving concentration factors of 34-129. Finally, 5 g of citrus peels purified 5.40 L mining wastewater.
-
Permafrost Settlement Caused By Climate Warming In Alaska And The Estimation Of Its Damage Costs For Public InfrastructureClimate models and studies indicate that the changes in the northern latitudes will be serious and accelerated. Climate warming may impact structures in the northern latitudes through permafrost settlement affecting the performance of infrastructure and increasing costs for maintenance. The material presented is organized in three main chapters. Chapter 1 describes the motivation for the research. Chapter 2 addresses the permafrost settlement hazard in Alaska. I developed the Permafrost Settlement Hazard Index, which considered anticipated climate warming and ecological characteristics which regulate permafrost settlement. I found that the discontinuous permafrost region is at more risk due to permafrost settlement than other regions of Alaska. I also found that the correlation that the areas with high settlement hazard value have higher road maintenance costs. Chapter 3 is an estimate of damage cost caused by permafrost settlement related to climate warming in the field of public infrastructure. I concluded that climate warming may add about $106 million annually from 2010 to 2050 to annual costs for public infrastructure in Alaska. This amount of damage cost is the relative size of damage cost that is caused by climate warming. In order to understand the broader idea of adaptation methods, a case study of Alaska roads for discontinuous permafrost regions is presented in Chapter 4. Some alternative construction methods were chosen as adaptation methods. Then, the comparison of the cost effectiveness of each adaptation method was shown to identify the most economical option when the cost estimation includes the effect of the additional permafrost settlement caused by climate warming. I concluded that pre-thaw method was the most cost effective method. I also recommended Air-Cooled Embankment on a condition that coarse rocks are available to create a convection cell. Chapter 5 summarizes the research and indicates possibilities for future research directions. I employed an interdisciplinary approach combining engineering knowledge with environmental impact assessments, utilizing economic tools in estimating damage costs, and analyzing the cost effectiveness of adaptation options to climate induced permafrost settlement. Nevertheless, this interdisciplinary analysis was not intended as a civil engineer design but intended for these economic estimates.
-
Detecting Methane Ebullition In Winter From Alaskan Lakes Using Synthetic Aperture Radar Remote SensingMethane (CH4) is a greenhouse gas with a high radiative forcing attribute, yet large uncertainties remain in constraining atmospheric CH4 sources and sinks. While freshwater lakes are known atmospheric CH4 sources, flux through ebullition (bubbling) is difficult to quantify in situ due to uneven spatial distribution and temporally irregular gas eruptions. This heterogeneous distribution of CH4 ebullition also creates error when scaling up field measurements for flux estimations. This thesis reviews estimates of CH4 contribution to the atmosphere by freshwater lakes presented in current literature and identifies knowledge gaps and the logistical difficulties in sampling CH 4 flux via ebullition (bubbling). My research investigates various imaging parameters of space-borne synthetic aperture radar (SAR) to constrain current CH4 emissions from northern lakes. In a GIS spatial analysis of lakes on the northern Seward Peninsula, Alaska, comparing field data of ebullition to SAR, I found that SAR L-band backscatter from lake ice was high from lakes with CH4 bubbles trapped by lake ice and low from lakes with low ebullition activity. The 'roughness' component of a Pauli polarimetric decomposition of quad-pol SAR showed a significant correlation with the percentage of lake ice area containing CH4 bubbles and with CH4 ebullition flux. This indicates that the mechanism of SAR scattering from ebullition bubbles trapped by lake ice is single bounce. I conclude that SAR remote sensing could improve our ability to quantify lake ebullition at larger spatial scales than field measurements alone, could offer between-lake comparison of CH 4 ebullition activity, and is a potential tool for developing regional estimations of lake-source CH4.
-
The Hydrologic Regime At Sub-Arctic And Arctic Watersheds: Present And ProjectedThe wetlands in the Arctic Coastal Plain, Northern Alaska, support a multitude of wildlife and natural resources that depend upon the abundance of water. Observations and climate model simulations show that surface air temperature over the Alaskan arctic coast has risen in recent history. Thus a growing need exists to assess how the hydrology of these arctic wetlands will respond to the warming climate. A synthesis study was conducted combining the analysis of an extensive field campaign, which includes direct measurements of all components of the water balance, with a physically-based hydrologic model forced by downscaled climate projections. Currently, these wetlands exist despite a desert-like annual precipitation and a negative net summer water balance. Although evapotranspiration is the major pathway of water loss, there are multiple non-linear controls that moderate the evapotranspiration rates. At the primary study site within the Barrow Environmental Observatory, shallow ponding of snowmelt water occurs for nearly a month at the vegetated drained thaw lake basin. Modeling studies revealed that the duration and depth of the ponding are only replicated faithfully if the rims of low-centered polygons are represented. Simple model experiments suggest that the polygon type (low- or high-centered) controls watershed-scale runoff, evapotranspiration, and near-surface soil moisture. High-centered polygons increase runoff, while reducing near-surface soil moisture and evapotranspiration. Soil drying was not projected by the end-of-the century but differential ground subsidence could potentially dominate the direct effects of climate warming resulting in a drying of the Arctic Coastal Plain wetlands. A drier surface would increase the susceptibility to fire, which currently is a major part of the Alaskan sub-arctic but not the arctic landscape. High quality pre- and postfire data were collected in the same location in central Seward Peninsula, uniquely documenting short-term soil warming and wettening following a severe tundra fire. Overall, this research concludes that arctic and sub-arctic watershed-scale hydrology is affected by changes in climate, surface cover, and microtopographic structures. It is therefore crucial to merge hydrology, permafrost, vegetation, and geomorphology models and measurements at the appropriate scales to further refine the response of the Arctic Coastal Plain wetlands to climate warming.
-
Multi-Dimensional Frost Heave Modeling With Sp Porosity Growth FunctionThis dissertation presents a multi-dimensional frost-heave modeling with coupled heat transfer, moisture transfer, and mechanical analysis. A series of laboratory frost-heave tests was conducted to determine segregation potential (SP) values using the effect of cooling rate and overburden pressure in two different freezing modes. Regardless of the freezing mode, consistent SP values were obtained at the formation of the final ice lens. Continuous heave and water-intake measurements made it possible to determine the time at the formation of the final ice lens. The SP porosity growth function was developed using simulations of the growing ice lens and frozen fringe. The developed frost-heave model was verified by laboratory frost-heave tests in one dimension. The simulated temperature distribution and amount of heave were in good agreement with experimental values. The SP porosity growth function was then expanded to two dimensions to simulate the soil-pipeline interaction of an experimental buried chilled pipeline constructed in Fairbanks, Alaska in the early 2000s. A two-dimensional frost-heave simulation was conducted at the free-field area, where the influence of pipeline resistance in frozen ground was negligible. This model, which considers the effect of frozen soil creep on stress distribution due to temperature variation, analyzed the influence of stress fields on soil frost-heave susceptibility and deformation. Simulations of pipe displacement were conducted for two cases, with and without the use of the long-term creep characteristics of frozen soils. Using the long-term creep characteristics, the simulated result agreed well with the observed value, differing by only a few percentage points. However, without using long-term creep characteristics, the simulated pipe heave was approximately 75% of the observed heave because of an unrealistic stress buildup. Finally, the SP porosity growth function was expanded to predict soil-pipeline interaction around a frozen-unfrozen boundary. Temperature distribution was successfully predicted in both the pre-frozen soil and the unfrozen zones, as well as at the time when differential pipeline movement started. The developed three-dimensional frost-heave model could predict pipe movement and induced bending due to differential frost heave for a 20-year period.
-
Impact Of Freeze -Thaw On Liquefaction Potential And Dynamic Properties Of Mabel Creek SiltIn the early winter of 2002 (November), the Alaska Denali earthquake (Mw=-7.9) caused significant damage in partially frozen fine-grained soil and extensive liquefaction was observed in glacial fine-grained saturated soil surface deposits near Tok, Alaska. It illustrated that there was a need to evaluate the seismic response and liquefaction potential of fine-grain soil in cold regions; however, until now most of the research on the liquefaction phenomenon and seismic response were mainly about soil in non-cold regions. The seismic response and liquefaction potential of soils in cold regions, especially those of fine-grained nature, has not been studied thoroughly and therefore is not well-understood. This document presents a laboratory study on liquefaction potential and cyclic response of fine-grained soil in cold regions. As the main features of the soil in the ground of cold regions, temperature change at below freezing temperatures or near-freezing temperatures, and the seasonal climate change were evaluated on liquefaction potential, dynamic properties, and post-cyclic-loading settlement of fine-grained soils. Increasing temperatures from near freezing to the completely thawed temperature (i.e., 24�C, 5�C, 1�C, and 0.5�C) were used to thaw the frozen Mabel Creek silt to simulate temperature change on it, or the Mabel Creek silt experienced several freezing and thawing alternating processes (i.e., 1, 2, and 4 freeze-thaw cycles) to simulate seasonal climate change. Triaxial strain-controlled cyclic tests were conducted to evaluate liquefaction potential, dynamic properties, and post-cyclic-loading settlement. Based on this limited laboratory effort, results show that in most cases, temperature rise and freeze-thaw cycles can impact: (a) liquefaction potential, (b) dynamic properties and (c) post-cyclic-loading settlement of fine-grained soils. However, there was one case exception and this is decribed in the following sentence. When a fine-grained soil was conditioned in a partially frozen state, the possibility and threat of liquefaction significantly increased.
-
Biodegradation Of Petroleum And Alternative Fuel Hydrocarbons In Moderate To Cold ClimateMicrobial degradation of hydrocarbon fuels contaminating soil in the Arctic and subarctic environment is a relatively slow process. Nevertheless, due to transportation and logistical limitations in rural Alaska, biodegradation might be the best and cheapest contaminant removal option. The aim of this thesis was to investigate the environmental effects on biodegradation by naturally occurring microorganisms for some innovative hydrocarbon fuels and to determine the overall fate of hydrocarbons in soil, including degradation by fungi and bacteria, volatilization, and transport in the soil. Three major types of fuels were investigated in small scale microcosms and larger soil columns: conventional diesel as a control substance, synthetic diesel (arctic grade Syntroleum) and different types of fish oil based biodiesel. The environmental conditions investigated included different soil types (sand and gravel), different temperatures (constant 6�C, 20�C, and fluctuating between 6 and 20�C), moisture levels (from 2% to 12% GWC), fuel concentrations (from 500 to 20,000 mg fuel/kg soil) and nutrient dosages (0 or 300 mg N/kg soil). Microbial response times and growth phases were also investigated for different inoculum types. Conditions of 20�C, 300 mg N/kg soil, sand, ?4000 mg of fuel/kg soil and ?4% GWC were favorable for bioremediation, with a short lag phase lasting from one day to less than a week, and pronounced peaks of daily CO 2 production between week 2 and 3. At suboptimal conditions, all phases were extended and slow, however at low temperatures steady metabolization continued over a longer time. The relative importance of fungal and bacterial remediation varied between fuel types. Diesel fuel degradation was mainly due to bacterial activities while fish biodiesel degradation occurred largely by mycoremediation. For Syntroleum both bacterial and fungal remediation played key roles. Volatilization contributed up to 13% to overall contaminant removal. In soil columns, degradation was slower than in microcosms, due to an uneven concentration profile of contaminants, nutrients and oxygen with depth. In general, biodegradation showed promising results for soil remediation and the alternate fuel types were more biodegradable compared with conventional diesel fuel.
