Browsing by Author "Martin, James R."

Now showing 1 - 7 of 7
  • Thumbnail Image
    Deep Energy Foundations: Geotechnical Challenges and Design Considerations
    Abdelaziz, 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 The heat energy is fed into the ground for cooling in the summer and withdrawn from the ground for heating in the winter.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.
  • Thumbnail Image
    Finite element modeling of contaminant transport through confined disposal facilities
    Tyler, Timothy N. (Virginia Tech, 1996)
    The US Army Corps of Engineers is responsible for regular dredging of shipping channels which produces about 300 million yd³ of dredged sediments annually. Many of these sediments have to be contained within confined disposal facilities (CDFs) due to the presence of heavy metals, PCB’s and other harmful constituents within the pore water of the dredge soils. However, these contaminants frequently seep back into the water from which the dredge was removed. The primary objective of this research was to modify the existing finite element program POLUT2D to evaluate the rate and quantity of contaminant transport through CDFs. Two actual field problems were evaluated using the modified program. One of these problems was a new CDF to be located along the US coast and the other was the existing Buffalo Harbor Dike facility located on Lake Erie in Buffalo, New York. The analyses of the coastal facility indicated that a cumulative quantity of about 43 kilograms of arsenic will seep back into the bay at the end of 50 years following filling of the CDF with arsenic contaminated dredge. Analyses of the Buffalo Harbor facility indicated that about 45 kilograms of chlorobenzene seeps annually into Lake Erie from the dredge material contained within this structure. Sensitivity analyses were also performed to evaluate the effect of soil properties, boundary conditions, etc. on contaminant transport through CDFs. The results indicated that some soil properties such as unit weight, molecular diffusion, and transverse dispersivity have little impact on contaminant transport. Other properties, such as the distribution coefficient and the longitudinal dispersivity, have only a slight to moderate impact on contaminant transport, while the coefficient of hydraulic conductivity can have a significant impact on contaminant transport though CDFs. Analyses also indicated that tidal fluctuations and infiltration from precipitation impact contaminant transport and must be modeled. Additional studies indicated that a slurry trench may provide better containment than a soil liner, and that a combination of a slurry trench and soil cover can reduce contaminant loading by a factor of about 4 depending on the thickness of the soil cover.
  • Thumbnail Image
    Implications from a geotechnical investigation of liquefaction phenomena associated with seismic events in the Charleston, SC area
    Martin, James R. (Virginia Tech, 1990)
    First-hand accounts of sand boils and other liquefaction-related phenomena associated with the Charleston, SC earthquake of 1886 provide clear evidence that liquefaction was common in this event. Recent geologic investigations in the Charleston area have found evidence for the repeated liquefaction of sandy soils in the Charleston area due to recurring large seismic events. Although this information has led to an improved understanding of seismicity in the Charleston region, little hard data exists in terms of ground motion characteristics or levels of seismic loading. A two-year field investigation was undertaken by Virginia Tech to study the liquefaction findings associated with the 1886 event from the perspective of geotechnical engineering. This involved defining the engineering parameters of the Charleston soils on the basis of in-situ and laboratory tests, and estimating the levels of seismic loading required to produce the observed liquefaction phenomena. Of the sites where field tests were performed, the surficial soils were largely formed from ancient beach ridge deposits. The findings showed that soil conditions within these deposits are appropriate for liquefaction. Also, there is clear evidence that soils as old as 230,000 years have liquefied multiple times in the past 10,000 years. Many of these soils remain susceptible to liquefaction at relatively low levels of seismic shaking, although there is some evidence for progressive densification. With respect to the seismic loadings, evidence is presented which suggests that both the magnitude and peak acceleration of the 1886 earthquake were less than what has been proposed by the seismological community (M = 7.7 and 0.5 - 0.6g peak acceleration). The findings of this study indicate that for an M = 7.5 event, peak accelerations in the 0.3 to 0.4g range would serve to explain the observed 1886 liquefaction phenomena. If it is assumed that the magnitude of the 1886 earthquake was less than 7.5, then the estimated peak accelerations increase.
  • Thumbnail Image
    Partitioning Uncertainty for Non-Ergodic Probabilistic Seismic Hazard Analyses
    Dawood, Haitham Mohamed Mahmoud Mousad (Virginia Tech, 2014-10-29)
    Properly accounting for the uncertainties in predicting ground motion parameters is critical for Probabilistic Seismic Hazard Analyses (PSHA). This is particularly important for critical facilities that are designed for long return period motions. Non-ergodic PSHA is a framework that allows for this proper accounting of uncertainties. This, in turn, allows for more informed decisions by designers, owners and regulating agencies. The ergodic assumption implies that the standard deviation applicable to a specific source-path-site combination is equal to the standard deviation estimated using a database with multiple source-path-site combinations. The removal of the ergodic assumption requires dense instrumental networks operating in seismically active zones so that a sufficient number of recordings are made. Only recently, with the advent of networks such as the Japanese KiK-net network has this become possible. This study contributes to the state of the art in earthquake engineering and engineering seismology in general and in non-ergodic seismic hazard analysis in particular. The study is divided in for parts. First, an automated protocol was developed and implemented to process a large database of strong ground motions for GMPE development. A comparison was conducted between the common records in the database processed within this study and other studies. The comparison showed the viability of using the automated algorithm to process strong ground motions. On the other hand, the automated algorithm resulted in narrower usable frequency bandwidths because of the strict criteria adopted for processing the data. Second, an approach to include path-specific attenuation rates in GMPEs was proposed. This approach was applied to a subset of the KiK-net database. The attenuation rates across regions that contains volcanoes was found to be higher than other regions which is in line with the observations of other researchers. Moreover, accounting for the path-specific attenuation rates reduced the aleatoric variability associated with predicting pseudo-spectral accelerations. Third, two GMPEs were developed for active crustal earthquakes in Japan. The two GMPEs followed the ergodic and site-specific formulations, respectively. Finally, a comprehensive residual analysis was conducted to find potential biases in the residuals and propose models to predict some components of variability as a function of some input parameters.
  • Thumbnail Image
    Q Models for Lg Wave Attenuation in the Central United States
    Conn, Ariel (Virginia Tech, 2013-03-22)
    A series of small- to moderate-sized earthquakes occurred in Arkansas, Oklahoma and Texas from 2010 to 2012, coinciding with the arrival of the EarthScope Transportable Array (TA). The data the TA recorded from those earthquakes provide a unique opportunity to study attenuation of the Lg phase in the mid-continent and Gulf Coastal region. The TA data reveal previously unrecognized regional variability of ground motion propagation in the central United States. A study of the Fourier amplitude spectra shows the Lg phase exhibiting strong attenuation for ray paths from Arkansas, southwest through the Ouachita Orogenic Belt and into central Texas, and south into the Gulf Coastal region. Less attenuation is seen in central Texas for ray paths extending directly south from Oklahoma, though attenuation remains strong along the Gulf Coast. In contrast, ray paths to the north, regardless of source location, exhibit very little attenuation, especially in northern Missouri and southern Iowa. Regression models that incorporate near-receiver (distance-independent) attenuation due to thick sediments in the Gulf Coastal Plain successfully reduce path-related bias in the regression residuals for stations near the Gulf Coast. Dividing the central United States into three regions (the Gulf Coastal Plain, the Great Plains and the Midwest) further reduced bias, and allowed for the development of Q models in the Gulf Coastal Plain and the Great Plains. In the Gulf Coastal Plain, the Q model for that part of the ray path through the basement, from the earthquake to the base of the sediment deposits below the receiver, was found to be Q=(295±11)*f^(0.645±0.029). The model for attenuation in the sediment section near the receiver in the Gulf Coastal Plain is Q=(72±6.7)*f^(0.32±0.06) (velocity through the sediments is unconfirmed but thought to be approximately 1 km/s). The Q model for the Great Plains is  Q=(692±61.3)*f^(0.43±0.07). The Midwest region exhibited extremely complicated behavior: the data indicate little or no attenuation of amplitudes in the frequency band from approximately 0.7 to 2.0 Hz. As a consequence, Q in the Midwest region in that frequency range could not be realistically determined.
  • Thumbnail Image
    A study of the effects of differential loadings on cofferdams
    Martin, James R. (Virginia Polytechnic Institute and State University, 1987)
    Conventional design of cellular cofferdams is largely based upon semi-empirical concepts derived from classical earth pressure theories. Recent studies have suggested that most existing design methods are excessively conservative. In part, this derives from an inability to fully describe the true, relatively complex soil-structure interaction process which occurs in the flexible cellular cofferdam. In addition to the apparent conservatism in the conventional theories, they provide no means to predict movements of cofferdams. This deficiency has become more important with time, since performance and safety monitoring systems are largely oriented towards measuring deformations, and it is not possible to define reasonable levels of movements before construction. Further, finite element analysis techniques are being developed which are designed to predict cofferdam deformations, but the means for verifying the predictions are not definitive because of the lack of a broad data base on cofferdam performance. This investigation is directed towards providing a data base through the documentation and comparison of five case histories where instrumentation was used to monitor the behavior. Primary consideration was given to the response of the cofferdams under differential loading. In the course of the investigation, the response of each cofferdam was documented and dissected in terms of the behavior at each stage of the differential loading. A strong correlation is found to exist between the lateral cell deflection and the level of differential loading, with the exact nature of the correlation depending on certain key parameters including cell foundation, cell fill material, cell width to height ratio, presence of a stabilizing berm, and nature of loading. It is found for conservatively designed cells that the response falls into a predictable pattern which can be characterized in terms of non-dimensionalized parameters for both normal and more severe levels of loading. In addition to deformations, information is provided on interlock tensions where available. The results are believed to provide a baseline for cofferdam behavior that can be useful in gaging the expected behavior of other cofferdams and for verifying the accuracy of new forms of predictive tools such as the finite element method.
  • Thumbnail Image
    The undrained behavior of saturated, dilitant silts
    Rose, Andrew Thomas (Virginia Tech, 1995-01)
    An extensive literature review and experimental study were performed to investigate whether cavitation and dissolved gases exiting solution from soil pore water are the cause of the erratic undrained behavior often observed in triaxial tests on saturated, dilatant silts. The literature indicates that ground water contains various amounts of dissolved gases and that gases dissolved in soil pore water will have sufficient time to exit solution to some extent, due to the pore pressure reductions which occur during sampling and unconsolidated-undrained triaxial tests. The exit of dissolved gases from solution would increase the soil volume and affect its undrained behavior. Experiments were performed on saturated silts to measure the pore pressure reductions which occur during sampling and unconsolidated-undrained triaxial tests. The amount of dissolved air that could come out of solution and the desaturation that a saturated soil sample could experience were also estimated. Gas bubble formation and growth within the pores of a saturated silt could affect intergranular forces and influence the stress-strain behavior of the soil in undrained tests. Variations in the amount of dissolved gas exiting solution and forming bubbles from one specimen to another could be the cause of the erratic undrained behavior often observed for saturated silts. Bubble growth within the soil pores is believed to have lead to abrupt strain-softening in a number of the undrained tests performed in this research. Variations in specimen disturbance may also contribute to the erratic behavior observed in undrained tests on silts. Disturbance levels and their influence on soil behavior are difficult to quantify. Due to the unusual properties of water under negative pressure, the initial value of pore water pressure within the soil appears to have a direct influence on the undrained strength of the soil. As a result, laboratory pore water pressures should be similar to in-situ pore water pressures, in order to give reasonable undrained strength measurements. The findings of this research are believed to be worthy of further study.