ORCID Identifier(s)

0000-0002-6809-5953

Graduation Semester and Year

2018

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Civil Engineering

Department

Civil Engineering

First Advisor

Anand Puppala

Abstract

The stability and serviceability of earthen embankment structures such as dams and levees are extremely crucial to avoid the catastrophic consequences of the failure of these structures. Such man-made geo-structures are usually stable under normal working conditions; however, the stability and subsequent functionality may be affected during earthquake events. Hence, the evaluation of seismic response and structural stability of earthen dams is an important facet in the field of geotechnical earthquake engineering. Dams and levees built in earthquake-prone regions are usually designed to withstand expected seismic events, and in-depth time-history-based dynamic analyses are typically performed to assess the behavior of these structures during earthquakes. However, earthen dams located in regions of newly declared induced-seismicity, like Texas, may not have been specifically designed to withstand these dynamic excitations. Hence, it is imperative to evaluate the performance of dams and levees located in such zones of induced seismicity. In this study, the stability of the Eagle Mountain dam, an 85-year-old hydraulic-fill dam, located in Fort Worth, Texas, is evaluated. Historical evidence concerning the poor performance of hydraulic-fill dams around the world during earthquake events further necessitates the assessment of seismic stability of the Eagle Mountain dam. Moreover, there is an inherent variability associated with the material properties along the body of the dam due to the hydraulic-fill method of construction that is not often captured in the traditional method of analysis. In this research, a framework is developed to study the seismic response and stability of hydraulic-fill dams incorporating the effect of material variability and induced seismicity. Three-dimensional models of the dam, depicting the variations in different shear strength properties, were developed by interpolating the in-situ test results using geostatistics-based kriging analysis. These models along with additional available bore log information were used to assign the material properties to the finite-element models of the dam. In the absence of earthquake time-history data recorded at the dam site, a new natural-frequency-based approach was devised to select the acceleration-time data required for the analysis. A novel method was also developed to determine the strain-dependent natural frequency of the earthen embankment structures. To comprehensively characterize the performance of the dam in the event of probable earthquakes, a broad spectrum of earthquake data having varying peak accelerations and frequency contents were selected. Extensive stability analyses, including static, pseudo-static, Newmark deformation, and dynamic analyses, were performed to identify the critical sections of the dam. A reliability-based pseudo-static analysis and a sensitivity analysis were also performed to gauge the effect of uncertainty associated with the estimation of the strength parameters and small strain shear modulus of subsurface layers, respectively. Results indicate that the dam is safe under static conditions and during earthquakes with peak ground accelerations (PGA) of 0.02g, similar to what the dam has already experienced in the past. Moreover, the dam is expected to be safe during earthquakes with PGA less than 0.09g, provided that the predominant frequency of the earthquake is not close to the natural frequency of the dam. Some parts of the upstream shell and foundation sand layers, especially near the toe of the dam, may liquefy. However, flow liquefaction of the foundation sand layers is not expected to happen. The middle portion of the dam, from stations 14.5 to 27, were found to be the most critical, based on the results of the pseudo-static and dynamic analyses.

Keywords

Hydraulic-fill dam, SASW, Slope stability, Liquefaction, Natural frequency, Reliability analysis, Seismic response

Disciplines

Civil and Environmental Engineering | Civil Engineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

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