Stability of rock on beaches

Stability of rock on beaches

Ye, L.

Schiereck, G.J. (mentor)
Fontijn, H.L. (mentor)
D' Angremond, K. (mentor)

Civil Engineering and Geosciences

Hydraulic Engineering

1996-08-01

This report is a graduation thesis of a fourth-years student of the Delft University of Technology, Faculty of civil Engineering. The object of this thesis is to research the stability of stones on a mild slope under wave attack. A possible application is the protection of a pipeline crossing a beach exposed to hydrodynamic forces. For many years, a lot of research has been done on the stability of rock on slopes under wave attack. But until now, there is no systematic description of the stability of rock in the breaking zone on gentle slopes under irregular waves, and only empirical or semi-empirical design rules are available. The idea for this graduation thesis is to use the method of Jonssen & Sleath (1978) and the method of Rance & Warren (1968) dealing with the static stability of stones in oscillating flow on a horizontal bottom to predict the stability of stones on a gentle slope. In order to obtain this aim, the computer simulation programme ENDEC, which is able to predict the wave parameters on slopes relatively correctly, was used. with the help of the results of ENDEC the maximum velocity including the influence of energy dissipation due to breaking has been calculated. Finally, this maximum velocity and the other wave parameters calculated by ENDEC are substituted into the formulae of Rance & Warren (1968) to predict whether the stones placed on a gentle slope are going to move or not. This idea must be verified by experiments. Experiments were carried out in a large wave flume of the Laboratory of Fluid Mechanics at the Delft University of Technology. In order to get more systematic information on the stability of stones in the breaking region on mild slopes under irregular wave attack, four different stone types were tested on two different slopes. A JONSWAP energy spectrum was used to represent the irregular wave condition. The damage and the wave heights along the slope were measured during the experiments. Experimental results have shown that waves with lower wave steepness are not favourable to the stability of the stones. The stones with a large stone diameter lead to high stability. An increase of the stone diameter, however, is not an efficient way to make the stones more stable. The experimental results show that on a mild slope, an increase of the mass density is an efficient way to increase the stability of the stones. On a steep slope, however, an increase of the mass density is not an efficient way to increase the stability of the stones. And the transition from spilling to plunging waves is a continuous curve. Furthermore, the theoretical results using the maximum velocity and the experimental results show the same trends. Moreover, the theoretical methods could predict the influence of the wave height, the mass density, the wave steepness, the stone diameter and the slope angle on the stability of the stones quite well, except the influence of the mass density of the stones on a steep slope. The methods using the maximum velocity can be used to predict the stability of the stones in the breaking region on mild slopes under irregular wave attack.

rock stability
cobble beach
gravel beach

http://resolver.tudelft.nl/uuid:597b65b3-6e4d-495a-b86e-81213a439e61

Student theses

master thesis

(c) 1996 Ye, L.