Thesis defence N. Hermidas: flows

17 June 2019 12:30 - Location: Science Centre, TU Delft - By: webredactie

Clay-laden subaqueous gravity flows: flow structures, deposites and run-out distance. Promotor: Prof.dr. S.M. Luthi (CiTG).

Submarine gravity flows constitute the last link in the source-to-sink sediment transport chain. They are the main mechanism for the transportation of sediment from the shallower to the deeper parts of the ocean. Due to their great volume, mobility, and power, they pose a formidable threat to the offshore infrastructures. In addition, deposits of ancient submarine gravity flows host many hydrocarbon reservoirs.

The principle questions that were investigated in this study were: (1) How are the dynamics of subaqueous gravity flows related to their deposits?, and, (2) Why are these flows able to travel so far?
In an attempt to address these questions, a series of laboratory flume experiments and a series of rheometry tests were carried out on mixtures with different sediment concentrations composed of sand, silt, kaolinite clay, and tap water.

Based on the results obtained from the flume experiments a new classification for clay- rich subaqueous gravity flows was proposed. According to this classification, a clay-rich flow may fall within one of four distinct flow types. Study of the deposits emplaced by the experimental flows revealed some specific signatures for each flow type. The results suggest that the bottom sand layers in hybrid beds can be deposited gradually from the body of a variety of flows, including highly cohesive plug flows, due to shearing. According to the results obtained from the rheometry tests it was proposed that the run- out distance and the structures of clay-laden subaqueous gravity flows are to a large extent dictated by the rheology of the materials inside these flows. A new rheological model was therefore proposed for the thixoelastic materials inside these flows. The model can capture the flow structures and the run-out distance of these flows. Finally using the rheological model a set of equations was proposed for modelling of free surface clay-laden gravity flows.

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