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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Dam-break Induced Scour and Pore Water Pressure Variations Around a Vertical Structure

Rajaie, Marieh 10 December 2021 (has links)
Coastal areas in many parts of the world are vulnerable to tsunami waves. Large tsunamis are strong enough to bring about a substantial amount of sediment mobilization. Several post-tsunami field investigations performed in recent years have documented destruction induced by scouring process. For example, the 1993 Nicaraguan earthquake centred 100km off the Nicaraguan coast caused devastating tsunami-induced scour around structures and bridges (Satake et al., 1993). Differences in the scour depths were related to soil properties, shapes of structures, and tsunami hydrodynamics (Jayaratne et al., 2016). Furthermore, depending on the soil permeability, the flow and pressure propagate at different speeds within the soil, which affects water table fluctuations and the soil strength (e.g., Tonkin et al., 2003; Yeh and Li 2008). The primary objective of this research was to study the effect of different inland-propagating dam-break bore heights on pore pressure variations and scour evolution in saturated beds with two different bed slopes (i.e., zero and +5% slope) by performing comprehensive laboratory studies at a 1:40 scale. To achieve the objective, tsunami-like dam-break bores generated by rapidly opening a swing gate and propagated towards and over a sediment section and hit a structure centred within a sediment bed. The secondary objective of this experimental investigation was finding a relation between scour depths and pore pressure values as a function of still-to-impoundment water depth ratio. The results of this experimental investigation showed that effective pore pressures were consistently greater in the front face of a model than in the side face. Besides that, the highest effective pore pressures took place near the saturated bed surface. Such that, due to the propagation of supercritical bores the maximum effective pore pressure in the bottom of the front corner was 50% larger than the exact same location in the side face. While, this difference decreased to 10% in the case of subcritical bores. For the same hydrodynamic bore conditions, the maximum difference between effective pore pressure in the two faces of the model reduced by 70% in the inclined bed test than the horizontal bed tests and this difference was only 15%. However, the peak effective pore pressure around the model doubled in the inclined bed tests compared to the horizontal ones. The 5% upsloping decreased the maximum scour depths by two times as a result of the same hydrodynamic loading conditions.

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