Civil & Environmental Engineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2753
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Item Stress-Controlled Versus Strain-Controlled Triaxial Testing of Sand(1994) Alqutri, Samir Ahmed; Goodings, Deborah J.; Civil Engineering; University of Maryland (College Park, Md); Digital Repository at the University of MarylandThe purpose of this research was to compare the strength characterizations of Mystic White Silica Sands using stress-controlled loading versus strain-controlled loading in a standard compression triaxial tests. To this end one hundred sixty-six tests were conducted involving two types of quartz sand, one fine MWSS45 and one medium coarse MWSS18 , tested at three low to intermediate confining stresses of 14 kN/m2, 28 kN/m2 and 55 kN/m2 with only one specimen diameter size of 71.1 mm. Of the one hundred sixty-six tests, eighty-six were stress-controlled tests and eighty were strain-controlled tests. All specimens were dry, but both loose and dense specimens were tested. The results were evaluated individually and as group. Comparison of the two types of loading tests were evaluated for repeatability, stress-strain characteristics and strength parameters. The plots show that stress-controlled loading in general gives more reproducible results with smoother. steeper stress-strain plot s and a larger average deviator stresses at failure than strain-controlled loading at all three levels of confining stresses for both sands. This results in somewhat larger values of Φ' . Stress-controlled specimens were stiffer and failed with a clear cut failure surface while strain-controlled specimens mostly barreled.Item SCALING OF SURFACE ENERGY FLUXES USING REMOTELY SENSED DATA(2001) French, Andrew Nichols; Brubaker, Kaye L.; Civil and Environmental Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Accurate estimates of evapotranspiration (ET) across multiple terrains would greatly ease challenges faced by hydrologists, climate modelers , and agronomists as they attempt to apply theoretical models to real-world situations. One ET estimation approach uses an energy balance model to interpret a combination of meteorological observations taken at the surface and data captured by remote sensors. However, results of this approach have not been accurate because of poor understanding of the relationship between surface energy flux and land cover heterogeneity, combined with limits in available resolution of remote sensors. The purpose of this study was to determine how land cover and image resolution affect ET estimates. Using remotely sensed data collected over El Reno, Oklahoma, during four days in June and July 1997, scale effects on the estimation of spatially distributed ET were investigated. Instantaneous estimates of latent and sensible heat flux were calculated using a two-source surface energy balance model driven by thermal infrared, visible- near infrared, and meteorological data. The heat flux estimates were verified by comparison to independent eddy-covariance observations. Outcomes of observations taken at coarser resolutions were simulated by aggregating remote sensor data and estimated surface energy balance components from the finest sensor resolution (12 meter) to hypothetical resolutions as coarse as one kilometer. Estimated surface energy flux components were found to be significantly dependent on observation scale. For example, average evaporative fraction varied from 0.79, using 12-m resolution data, to 0.93 , using 1-km resolution data. Resolution effects upon flux estimates were related to a measure of landscape heterogeneity known as operational scale, reflecting the size of dominant landscape features. Energy flux estimates based on data at resolutions less than 100 m and much greater than 400 m showed a scale dependent bias. But estimates derived from data taken at about 400-m resolution (the operational scale at E l Reno) were susceptible to large error due to mixing of surface types. The El Reno experiments show that accurate instantaneous estimates of ET require precise image alignment and image resolutions finer than landscape operational scale. These findings are valuable for the design of sensors and experiments to quantify spatially-varying hydrologic processes.Item PERFORMANCE OF REPAIRED CONCRETE COLUMNS UNDER AXIAL LOADING(2019) Seyidoglu, Murat; Zhang, Yunfeng; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The purpose of this research was to determine the performance and axial load capacity of repaired reinforced concrete columns under compressive loading. While various concrete column strengthening methods, using concrete or carbon fiber reinforcing polymer (CFRP) jacketing, have been exhaustively researched, there is an insufficient amount of research regarding the performance of column repairs utilizing concrete removal and replacement. To research this topic, nine reinforced, one-third scale concrete columns were cast; and, six of these columns were repaired with conventional concrete repair methods recommended by the American Concrete Institute’s Guide to Concrete Repair (546-14). Shallow (extending up to the exterior faces of column ties) and deep repairs (extending behind the vertical bars) were performed at the bases of the columns by chipping the concrete with a handheld chipping hammer and patching with a shrinkage compensated repair mortar as it is commonly done for repairing corrosion related spalls. Results of the axial compression loading tests and failure patterns of the repaired columns were compared to that of the control samples. It was found that all repaired concrete columns achieved comparable load capacity values and exhibited the same failure mode as the intact columns.Item Environmental Advocacy Messages: Relationships Between the Messages that Constituents Send to Decision Makers and Organizational Engagement(2019) Choy, David F; Skibniewski, Miroslaw J; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Environmental advocacy organizations aim to help citizens contact their policymakers, to recruit new members, and to increase their contacts’ level of engagement with organization issues. They use online petitions and form-letter services for these purposes. These services put citizens in contact with policymakers and encourage citizens to take follow-up actions, such as sending another message, referring a friend, or making a donation. While these services effectively recruit members, they marginally influence policymakers. To increase influence, organizations now ask petitioners to include personal messages in their communications. This dissertation asks if text analysis of these personal messages can help advocacy organizations further fulfill their recruitment and engagement goals. It investigates text-metrics both for predicting engagement from existing contacts and for services, such as chatbots, to suggest follow-up actions to new contacts. Methods employ rule-based text analysis tools (LIWC, VADER, Flesch Reading Ease, and Regular Expressions) to pilot the use of pronouns, sentiment, writing complexity, and the identification of personal stories as predictors of engagement. Data include over two million messages and nearly 500,000 personal messages from over 150,000 individuals supporting sustainable policies and projects. Results reveal relationships between messages and two engagement factors: (1) the number of messages that groups of contacts send and (2) payment of membership dues. Results also bolster research that highlights the importance of identifying contacts who can share stories about how environmental issues have affected them. Conclusions encourage advocacy organizations and policymakers to analyze messages to increase engagement and understand constituency support of policies and projects. Future work may integrate text analysis into membership models and advocacy services. Future work may also improve personal story classification and investigate machine-learning for identifying potential members.Item MULTIMODAL TRAVEL BEHAVIOR ANALYSIS AND MONITORING AT METROPOLITAN LEVEL USING PUBLIC DOMAIN DATA(2019) PENG, BO; Zhang, Lei; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Travel behavior data enable the understanding of why, how, and when people travel, and play a critical role in travel trend monitoring, transportation planning, and policy decision support. Conventional travel behavior data collection methods such as the National Household Travel Survey (NHTS) have been the primary source of travel behavior information for transportation agencies. However, the relatively high cost of traditional travel surveys often prohibits frequent survey cycles (currently once every 5-10 years). With decision makers increasingly requesting recent and up-to-date information on multimodal travel trends, establishing a sustainable and timely travel monitoring program based on available data sources from the public domain is in order. This dissertation developed advanced data processing, expansion, fusion and analysis methods and integrated such methods with existing public domain data into a comprehensive model that allows transportation agencies to track monthly multimodal travel behavior trends, e.g., mode share, number of trips, and trip frequency, at the metropolitan level. Advanced data analytical methods are developed to overcome significant challenges for tracking monthly travel behavior trends of different modes. The proposed methods are tailored to address different challenges for different modes and are flexible enough to accommodate heterogeneous spatial and temporary resolutions and updating schedules of different data sources. For the driving mode, this dissertation developed reliable methods for estimates of local road VMT, various temporal adjustment factors, truck percentage factors, average vehicular occupancy, and average trip length based on additional data from the Travel Monitoring Analysis System and the most recent regional household travel survey to translate HPMS data into monthly number of vehicular and person driving trips for a metropolitan area. For the transit mode, this dissertation collectively exhausted detailed transit network geo-data to complement NTD and developed advanced geo-analysis and statistical methods tailored to the service network of different types of operators to accurately and reliably allocate ridership data to the metropolitan area of interest, and to allocate annual ridership data to each month. The data for non-motorized is even more sparse, although the local government has growing interests and efforts on collecting such data. A two-step statistical model is developed to derive the trend for non-motorized modes and then integrating such trends with base-year number of trips number from most recent household travel survey conducted in the metropolitan areas of interest. Based on the number of trips by modes estimated using the proposed methods, the monthly trend in mode share can be timely estimated and continuously monitored over time for the first time in the literature using public domain data only. The dissertation has demonstrated that it is feasible to develop a comprehensive model for multimodal travel trend monitoring and analysis by integrating a wide range of traffic and travel behavior data sets of multiple travel modes. Based on findings, it can be concluded that the proposed public-domain databases and data processing, expansion, fusion and analysis methods can provide a reliable way to monitor the month-to-month multimodal travel demand at the metropolitan level across the U.S.Item INVESTIGATING THE DYNAMICS OF VOLATILE SULFUR COMPOUNDS FROM PRIMARY AND SECONDARY SYSTEMS IN WASTEWATER RESOURCE RECOVERY FACILITIES(2019) Bazemo, Ulrich Yoan Yanick; Torrents, Alba; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study quantifies volatile sulfur compounds (VSCs) emissions from Wastewater Resource Recovery Facilities (WRRFs) and investigate their mechanisms of generation. In primary treatment, of the VSCs analyzed, hydrogen sulfide (H2S) and methyl mercaptan (MM) concentrations in the off gas were dominant, while dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) were under their odor threshold for most sampling dates. H2S emission in primary settling tanks was mainly the result of the stripping of dissolved sulfide (64%) generated in the sewers. MM emission was more dependent on the conditions in the primary clarifiers (only 16% stripping). Most significant prevention of odor emission in primary settling tanks can be achieved by managing biofilms and microbial reactions in the sewer network. This would control the biomass seeding and fermentation product availability in the primary settling tanks directly and will decrease the observed kinetics of H2S and MM production. Overall, management of sludge blanket heights and thus avoiding time at low oxidation reduction potential (ORP) minimized odor emission independent of sewer conditions. Our investigations in secondary reactors have shown that MM was 2 to 3 order of magnitude higher than dissolved MM in primary effluent, revealing that the production of MM took place in the activated sludge process itself, and the stripping of MM from the feed was very minimal. Furthermore, data showed that the depth of secondary sludge blanket plays an important role on the extent of MM emission. At high sludge blanket height, high MM emission was observed. It was concluded that low ORP conditions in sludge blanket, selector zones and RAS was the major source of VSCs. Increasing ORP could decrease odor emissions by targeting the zones where MM is emitted. This could be achieved by addition of nitrate in secondary settling tanks.Item PREVENTION AND TREATMENT OF POLYCHLORINATED BIPHENYLS IN SEDIMENTS - SOURCES AND SOLUTIONS(2019) Jing, Ran; Kjellerup, Birthe Veno; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)PCBs are classified as one of the persistent organic pollutants (POPs) with high toxicity and have undesirable effects on the environment and on humans. Once released into the environment PCBs could bioaccumulate within the food chain, due to their high affinity for organic materials. Recently, studies indicated PCBs can potentially enter a wastewater treatment plant (WWTP) system and be discharged via wastewater effluents thereby further contaminating the downstream environments. This study evaluated the potential for bioremediation of polychlorinated biphenyls (PCBs) in the effluent from a large WWTP. It was found that the continuous effluent was responsible for the majority of the discharged PCB into the receiving river (1821 g for five years), while the intermittent discharge contributed 260 g over the five years. The average number of chlorine per biphenyl for the detected PCB congeners showed a 19% difference between the two types of effluent, which indicated a potential for organohalide respiration of PCBs during the continuous treatment. This was further supported by a high level of tri-, tetra- and penta- chlorinated congeners accounting for 75% of the anaerobically respired PCBs. Potential for aerobic degradation and thus biomineralization of PCBs were identified for both effluents. In addition, the similarity of organohalide respiring (OHR) microbial populations in biosolids and intestinal human biofilms was determined by applying a bioinformatics approach. The OHR populations of the communities were analyzed from existing American and Chinese human intestinal microbiomes. The results of the biosolids analysis showed increased amounts of products from PCB respiration. Simultaneously, experiments with organohalide respiration of PCE in biosolids samples showed significant decreases in PCE concentration after 46 days (28-92%). Subsequently, it was evaluated if the OHR microbial populations in biosolids were similar to those present in intestinal human biofilms by applying a bioinformatic approach. The OHR populations of the communities were analyzed from existing American and Chinese human intestinal microbiomes. The overall groups Proteobacteria, Bacteroides, Actinobacteria, and Firmicutes phyla dominated the microbiomes in all datasets. The OHR groups in biosolids and intestinal biofilms included Dehalogenimonas, Dehalobacter, Desulfitibacter, Desulfovibrio, Sulfurospirillum, Clostridium, and Comamonas. The results of this study showed that several OHR phyla were present in all samples independent of origin. Wastewater and intestinal microbiomes also contained OHR phyla. Finally, biofilms made up by the OHR bacteria Dehalobium chlorocoercia DF-1 were inoculated on the surface of the pinewood biochar particles. The mole percent of the total PCE in the headspace decreased from 100% to 70.4%±17.6% for the rest of nine mesocosms which suggested that the D. chlorocoercia DF-1 biofilm converted PCE to TCE. The gene copy numbers of DF-1 biofilm from nine mesocosms which are ranging from 1.95×108 to 8.30×108 gene copies/g pinewood biochar. The biochar-biofilms were subsequently applied to PCB contaminated sediment from the Grass River in Michigan, USA. The goal was to evaluate the organohalide respiration of the PCB contaminated sediments in the absence/presence of the biofilm and free-floating inoculum.Item RELATING RISKS TO PAY FACTORS FOR HIGHWAY PAVEMENTS THROUGH MONTE CARLO SIMULATION(2019) Zhao, Yunpeng; Goulias, Dimitrios G; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The majority of State Highway Agencies (SHAs) now employ statistical-based specifications for the acceptance of highway materials and pavement construction. The parameters of these statistical acceptance plans are specified based on engineering judgment and may result in a high level of risk to both agency and contractor. In order to appropriately apply such specifications to the pavement construction industry, the associated production quality (i.e., materials and construction variability) needs to be well understood by all parties involved and its potential impacts require to be assessed. To address this objective of this study was to: (i) quantify the risks to the agencies and contractors (i.e., Type I and Type II errors); (ii) examine how the key components in a statistical acceptance plan impact its performance; and, (iii) identify a methodology to balance the risks and pay factors. Risk and pay factor analysis were conducted for both single and multiple quality characteristics through Monte Carlo simulation, and the development of Operating Characteristic, OC, curves. Furthermore, case studies were presented to demonstrate the value of the analyses proposed in this study. The methodology and findings identified in the study can be applied elsewhere to evaluate the acceptance plans and the associated risks pertinent to pavement construction and the production of highway materials.Item Seismic Resilience Study of Steel Concentrically Braced Frame Structure with Dual Viscous and Metallic Hysteretic Damper(2019) Xu, Jianshu; Zhang, Yunfeng; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Steel concentrically braced frames（CBF）are popular seismic resistant structural systems widely used all over the world due to their high elastic stiffness and moderate ductility for many decades. However, conventional CBFs are subject to soft-story damage pattern which may lead to collapse caused by overly large drift concentrated in one story in strong earthquakes; measures to enhance the seismic resilience of CBFs is thus desirable. This study looks into quantifying the seismic resilience of CBFs with and without dual-action damping devices by following the newly released 2018 ed. FEMA P58 procedure. The dual-action damping device includes a viscous damper and metallic hysteretic dampers which are activated at different timing: viscous damper always active and effective in controlling story drift during small and moderate earthquakes, while metallic hysteretic dampers are activated only when the story drift exceeds a pre-specified value during strong earthquakes. A six-story steel CBF and a three-story steel CBF buildings designed by SAC Steel Project research (1999) are adopted as prototype building to demonstrate the effectiveness of dual-action damping device in enhancing the seismic resilience of CBFs. Nonlinear static analyses as well as nonlinear time-history analysis are performed to obtain the Engineering Demand Perimeters (EDP) required for seismic resilience evaluation. Collapse Fragility is developed based on incremental dynamic analysis (IDA) by SPO2IDA Tool. The distribution function of Decision Variables (DV), including Repair cost, Repair time, Casualties etc., is obtained through Monte-Carlo simulation of prior nonlinear time-history analysis EDP by Performance Assessment Calculation Tool (PACT). It is found from this study that the Collapse Risk and the Potential Loss of the prototype structure with dampers have been significantly reduced, suggesting the dual-action damping device provides a beneficial alternative for enhancing the seismic resilience of CBFs.Item Evaluating Gutter Filter Performance After 10 Years Operation(2019) Greenfield, Madeleine; Davis, Allen P; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Urban stormwater runoff contains various pollutants that degrade downstream water quality. Gutter filters, below-grade filtration devices that capture sheet flow, are an ideal stormwater control measure for urban retrofits because of their small footprint. A 10-year-old gutter filter system in Mt. Rainier, MD was monitored for 18 storm events over 13 months for total suspended solids, nitrogen, phosphorus, and copper, zinc, and lead in the downstream stormwater. The filters had received no maintenance since their construction. The stormwater quality was compared to studies conducted prior to installation and immediately after installation of the filters. Total Kjeldahl Nitrogen concentrations displayed a statistically significant increase since installation. All other pollutants did not show a significant change over the 10 years. Nonetheless, overall runoff water quality was not good. Event mean concentrations are comparable to highway runoff and annual pollutant loadings are comparable to untreated runoff from other urban drainage areas in the region.