Free-fall penetrometers (FFP) are useful instruments for the rapid characterization of seabed sediments. However, the interpretation of FFP data remains largely a skilled task. In order to increase the reliability of results obtained using these instruments, in both expert and non-expert hands, it is advantageous to establish well defined and repeatable procedures for instrument use and data interpretation. The purpose of this research was therefore to develop and refine methods for the interpretation of FFP data.
Data were gathered with the FFP Nimrod during two surveys following dredging in Sydney Harbour, Nova Scotia. The challenge of interpreting the data from these two surveys in an efficient and consistent manner was the basis of this work and led to the development of new techniques for improving resolution of the mud-line, identifying areas of erosion and deposition, and qualitatively evaluating the consolidation state of cohesive marine sediments.
The method developed for improving the resolution of the mud-line simply describes a procedure of combining the data from different accelerometers with different accuracies and ranges to more clearly define the point of impact with the sea-floor. The method developed to evaluate in-situ sediment consolidation state combines theories of self-weight consolidation and ultimate bearing capacity to predict a range of potential bearing capacities for normally consolidated cohesive sediments. Finally, by combining the previous two methods a third method is proposed for locating areas of potential erosion and deposition. / Master of Science / Human interaction with the marine environment takes many forms. For example, in the case of marine/civil engineering projects these interaction may include: erecting off-shore wind turbines, installing oil rigs, and building break waters. All of these activities involve installing structures with foundations on or attached to the seafloor. In order for these structures to be effective and for there foundation to not fail a knowledge of the physical conditions <i>at</i> the seafloor is required.
Physical characterization of the seafloor involves describing three interdependent processes: hydrodynamics (the movement of water), morphodynamics (the dynamic processes which shape the seafloor), and sediment dynamics (the movement of sediments). Together, these three form a complex and interacting feedback loop in which a change in one will affect the states of the others and eventually itself. For example, energetic hydrodynamic conditions may erode sediment from the seabed. As this sediment is transported and deposited elsewhere by the flow of water, the initial features which make up the seafloor, such as dunes, ripples, and sand-waves, are reshaped. These forms may grow or shrink, migrate, or be wiped out and replaced entirely. The changed shape of the seabed will then in turn influence the flow of passing waves, tides, and currents. The newly changed flow patterns then restarting the cycle anew. Understanding the interactions of these processes is vital to designing effective engineering works in the marine environment.
Free-fall penetrometers (FFP) are useful instruments for the rapid characterization of seabed sediments and can therefore provide information about the sediment dynamics at the seafloor’s surface. However, the interpretation of FFP data remains largely a skilled task. In order to increase the reliability of results obtained using these instruments, in both expert and non-expert hands, it is advantageous to establish well defined and repeatable procedures for instrument use and data interpretation. The purpose of this research was therefore to develop and refine methods for the interpretation of FFP data.
During two surveys in Sydney Harbour, Nova Scotia, data were gathered from the seafloor’s surface with the FFP <i>Nimrod</i>. The challenge of interpreting this data in an efficient and consistent manner was the basis of this work and resulted in the development of new methods and techniques for data interpretation and analysis. These methods will allow for the improved characterization of sediment processes and properties at the uppermost seafloor, contributing to a better understanding of the seafloor environment as a whole and improving engineering designs.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/73216 |
| Date | 13 October 2016 |
| Creators | Dorvinen, Jared Ian |
| Contributors | Civil and Environmental Engineering, Stark, Nina, Castellanos, Bernardo Antonio, Irish, Jennifer L. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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