Numerical modelling of coastal structures armoured with concrete units

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Title: Numerical modelling of coastal structures armoured with concrete units
Authors: Anastasaki, Eleni
Item Type: Thesis or dissertation
Abstract: Looking to a future where the structural stability of single concrete armour layers is based upon numerical investigation, this thesis addresses the first major task, which is the representation of real structures. Coastal structures armoured with concrete units are created in prototype dimensions in a numerical model with satisfied realism for first time. The available 3D computer model based on FEMDEM (the combined finite-discrete element method), which has the capability for multi-body simulation of complex shaped objects, was used. A major challenge was to develop a methodology for the numerical creation of concrete armour layers that would satisfy the stringent criteria required by the designers of breakwater units for on-site constructed ‘random’ and ‘interlocking’ systems. A novel feature to obtain realistically tight systems is the use of four initial types of regular orientations of units, which are sequenced appropriately on a pre-defined positioning pattern grid. This new methodology enables different armour layer models to be built, characterised and examined. The scope of the study is limited to dry conditions and performance under oscillatory loading is investigated by means of vibration. Design variables such as initial packing density, underlayer roughness and number of rows are evaluated and the technical criteria are challenged. The use of a different type of unit shape is also examined to show the potential of the developed technology. A set of analysis tools including accurate calculation of packing density on a local and global basis and the distribution of unit displacements after disturbance were developed to evaluate designs. It is confirmed that the packing density is the most important parameter, which influences the performance of armour layers; the tighter the packs, the less are the displacements of units under disturbance. A single armour layer with low number of rows of units also proved to be stable. It is easier for units placed on a relatively smooth underlayer to find tighter positions, causing higher values of total average packing density. But when disturbed, armour layers placed on a rough underlayer are more stable. The use of a different type of unit shape is also examined in this thesis, with the purpose to present the potential of the developed technology to such applications. Results may be considered to have limited applicability to the real behavior of structures under wave action. However, they provide some insights into how such complex coastal structures behave. This research constitutes a stepping stone on the way to models that accommodate wave action and will may one day improve the engineering design and understanding of movement of these concrete armour units.
Content Version: Open Access
Issue Date: Mar-2015
Date Awarded: Oct-2015
Supervisor: Latham, John-Paul
Sponsor/Funder: Engineering and Physical Sciences Research Council
Funder's Grant Number: EP/H030123
Department: Earth Science & Engineering
Publisher: Imperial College London
Qualification Level: Doctoral
Qualification Name: Doctor of Philosophy (PhD)
Appears in Collections:Earth Science and Engineering PhD theses

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