Browsing by Author "Muller, Gert Victor"

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    An appropriate size of toe rock for vertical seawalls
    (Stellenbosch : Stellenbosch University, 2016-12) Muller, Gert Victor; Schoonees, J. S.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT: The design and construction of an appropriate vertical seawall/breakwater is an important part of an engineering project since the incident and reflective wave forces acting on the vertical seawall cause severe turbulence at the toe of the structure. The continuous wave action makes the toe of the structure vulnerable towards the erosion of the seabed material and scouring. The determination of the size of the toe rock, needed for the toe of the rubble foundation, is under investigation in this study. The present empirical design formulas used to determine the adequate rock sizes are based on limited data in the relative foundation depth ranges of *0.35 ≤ d1/d ≤ 0.55+, where d represents the water depth and d1 the depth of the still water level above the foundation mound. In this thesis, the required information is provided regarding the response characteristics of the armour layer in transitional water depths. A hypothesis is thus put forward that for a certain fixed relative foundation depth (d1/d) and wavelength (L), the significant wave height, Hs, will have an exponential relationship with the number of rocks displaced in the armour layer of the toe of the vertical structure. Apart from the wave height, the influence of the wave period is also expected to affect the overall stability of the armour layer. The wave overtopping for the specific cross-sections is expected to be well within the overtopping rules stated in the literature and the rate is anticipated to increase gradually with an increase in the wave height and wave period. A series of physical model tests, conducted at the Council of Scientific and Industrial Research (CSIR) laboratory, was undertaken. It entailed setting up a two-dimensional model in a glass flume. By measuring the essential parameters, the hydraulic stability and response characteristics of the armour layer could be determined and analysed. The test results of the model confirmed the hypothesis stated. The evaluation of data proved that the results obtained by the author were an accurate representation of the response characteristics expected during the stability analysis. With the credibility of the results verified, a design approach was implemented to determine a proposed formula for the relative foundation depth ranges outside of the previous data in the literature. The proposed formula proved to be an accurate representation of the minimum stability numbers needed for the determination of an appropriate size of toe rock for vertical seawalls. The overtopping rates measured during the physical model tests were lower than the predicted values proposed by the EurOtop (2007). The scattered comparison of the results highlights the fact that there are still a lot of uncertainties not accounted for in the EurOtop (2007) formula for the estimation of overtopping for vertical structures with a wave recurve wall.