Browsing by Author "Abdelaziz, Sherif Lotfy Abdel Motaleb"
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- Deep Energy Foundations: Geotechnical Challenges and Design ConsiderationsAbdelaziz, Sherif Lotfy Abdel Motaleb (Virginia Tech, 2013-05-07)Traditionally, geothermal boreholes have utilized the ground energy for space heating and cooling. In this system, a circulation loop is placed in a small-diameter borehole typically extending to a depth of 200-300 ft. The hole is then backfilled with a mixture of sand, bentonite and/or cement. The loop is connected to a geothermal heat pump and the fluid inside the loop is circulated. The heat energy is fed into the ground for cooling in the summer and withdrawn from the ground for heating in the winter. Geothermal heat pumps work more efficiently for space heating and cooling compared to air-source heat pumps. The reason is ground-source systems use the ground as a constant temperature source which serves as a more favorable baseline compared to the ambient air temperature. A significant cost associated with any deep geothermal borehole is the drilling required for installation. Because Energy Piles perform the dual function of exchanging heat and providing structural support, and are only installed at sites where pile foundations are already required, these systems provide the thermal performance of deep geothermal systems without the additional drilling costs. Low maintenance, long lifetime, less variation in energy supply compared to solar and wind power, and environmental friendliness have been cited as additional Energy Pile advantages. Case studies show that they can significantly lower heating/cooling costs and reduce the carbon footprint. Energy cost savings for typical buildings outfitted with Energy Piles could be as much as 70 percent. The use of Energy Piles has rapidly increased over the last decade, especially in Europe where more than 500 applications are reported. Primary installations have been in Germany, Austria, Switzerland and United Kingdom. Notable projects include the 56-story high Frankfurt Main Tower in Germany, Dock E Terminal Extension at Zurich International Airport in Switzerland and the One New Change building complex in London U.K. Energy piles have seen very little use in the North America, only a handful of completed projects are known; Marine Discovery Center in Ontario, Canada, Lakefront Hotel in Geneva, New York and the Art Stable building in Seattle, Washington. Energy Piles are typically installed with cast-in-place technology (i.e. drilled shafts, continuous flight auger piles, micropiles etc.) while some driven pile applications are also reported. Other types of geotechnical structures in contact with the ground, such as shallow foundations, retaining walls, basement walls, tunnel linings and earth anchors, also offer significant potential for harnessing near-surface geothermal energy. Energy Pile design needs to integrate geotechnical, structural and heat exchange considerations. Geotechnical characteristics of the foundation soils and the level of the structural loads are typically the deciding factors for the selection and dimensioning of the pile foundations. The geothermal heat exchange capacity of an Energy Pile is a key parameter to be considered in design. Thermal characteristics of the ground as well as the heating and cooling loads from the structure need to be considered for the number of piles that will be utilized as heat exchangers. Therefore, the thermal properties of the site need to be evaluated for an Energy Pile application in addition to the traditional geotechnical characterization for foundation design. Energy Piles bring new challenges to geotechnical pile design. During a heat exchange operation, the pile will expand and contract relative to the soil as heat is injected and extracted, respectively. These relative movements have the potential to alter the shear transfer mechanism at the pile-soil interface. Furthermore, the range of temperature increases near the pile surface, though limited by practical operational guidelines, can have a significant effect on pore pressures generation and soil strength. This dissertation provides answers for several research questions including the long-term performance of Energy Piles, the applicability of the thermal conductivity tests to Energy Piles. Furthermore, it presents the results and a detailed discussion about the full scale in-situ thermo-mechanical pile load test conducted at Virginia Tech.
- Liquefaction Triggering Model for Subduction Zone EarthquakesAnbazhagan, Balakumar (Virginia Tech, 2021-09-14)Liquefaction is one of the major causes of ground failures during an earthquake. Recent evidence shows that the existing variants of the "simplified" liquefaction evaluation procedure lead to inaccurate results for megathrust earthquakes in subduction interfaces. To overcome this drawback and to achieve better prediction of liquefaction cases in subduction zones, this research intends to develop new empirical models that could be used for the prediction of liquefaction triggering in subduction zones. Towards this goal, new models for number of equivalent cycles (n_eq) and stress-reduction factor (r_d) have been proposed. The models are developed by regressing site response data obtained from 254 pairs of subduction ground motions and 77 representative soil profiles. To account for tectonic differences and magnitude scaling, separate models are developed for interface and intraslab earthquakes. The uncertainties involved in the proposed models are quantified through standard deviations of regression coefficients, event, site, and residual terms. The resulting models differ from other published models, especially the model for number of equivalent cycles. It was found that n_eq is greatly influenced by the fundamental site period. The model for r_d predicts higher values at shallow depths and lower values at deeper layers than other published models. Comparing the factors of safety against liquefaction with those from other existing models revealed that the use of models proposed in this research is more likely to reduce the "false positives" in liquefaction predictions, especially when design ground motion acceleration is high.
- Study and Evaluation of Traffic Responsive Control on a Large Arterial NetworkAbdelaziz, Sherif Lotfy Abdel Motaleb (Virginia Tech, 2008-08-04)Traffic responsive mode of operation with its two mechanisms, threshold-based and pattern matching, is considered one of the effective and efficient signal control modes. This operation mode is underutilized due to its cumbersome configuration procedure. The research presented in this thesis aims to give some guidelines regarding traffic responsive and issues that might improve the system performance. Four different issues related to traffic responsive are considered: The first issue is the generation of different traffic scenarios that drive the design of the system. This point is not limited to traffic responsive only but it is more general for different traffic engineering applications that need different traffic scenarios. The second issue is presenting an approach to implement traffic responsive control mode of operation in a large arterial network in Northern Virginia. Pattern matching mechanism is used for this application. Compared to time-of-day control mode, traffic responsive control saves up to 26.94% of the average delay and 21.13% of average number of stops for Reston Parkway network. The third issue is an attempt to improve the current threshold mechanism by relaxing the threshold constraints and using variable thresholds for different levels of plan selection parameters. The last issue is a study for the pedestrian effect on the performance of networks operating by traffic responsive control. The effects of pedestrian calls and pedestrian phases on traffic responsive control are compared and the results shows that pedestrian calls are better for low pedestrian volumes while pedestrian phases are better for high pedestrian volumes.