Hydro-geotechnical behaviour of porous coastal structures

Abstract

Theoretical modeling of the flow field in the vicinity of a porous coastal structure was carried out to investigate the hydro-geotechnical behaviour of such a structure. The area of interest consists of the regions in front of and within the structure and in the sub soil below the sea bed, resulting in three inter-related flow models, External Flow, Internal Flow and the Pore Pressure Response Models. In the External Flow Model, the governmg equations are based on the principles of conservation of mass and momentum and were solved numerically by an explicit finite difference method. The model was shown to yield the flow characteristics and the computed wave run-up, run-down and reflection coefficient were shown to be in qualitative agreement with the available empirical formulae. The governing equations in the Internal Flow Model are also based on the principles of conservation of mass and momentum and were solved by a mixed numerical technique involving a combined finite difference-method of characteristic scheme and a finite element method. The model was shown to represent the two dimensional nature of flow and yield satisfactory agreement with the experimental data for the position of the phreatic surface. In the Pore Pressure Response Model, the governing equation for the flow in the soil is based on the principle of conservation of mass with the generation of pore pressure represented by an empirical expression. An explicit finite difference method was used to solve it and the solution provides the complete time history of pore water pressure response due to cyclic wave loading. With the flow models shown to be capable of simulating the flow field in the vicinity of a porous coastal structure, this study forms a basis for further studies aiming at supplementing the design practices of such structures presently based on physical modeling and empirical formulations.