Under water unloading process of saturated sand through a small discharge opening - without the use of water jets

Under water unloading process of saturated sand through a small discharge opening - without the use of water jets

Van Aalderen, M.W.

Van der Schrieck, G.L.M. (mentor)
Biesheuvel, M. (mentor)
Miedema, S.A. (mentor)
Van Rhee, C. (mentor)

Civil Engineering and Geosciences

Hydraulic Engineering

2009-04-24

Royal Boskalis Westminster nv is an international group with a leading position in the world market for dredging services. In most practical cases a jet installation or a big discharge aperture is used for the fast unloading of a load of sand. When a relative small discharge opening, without the use of a jet installation, is used to unload a hopper, the unloading time will increase. Uncertain is how much longer this type of unloading will take and what kind of mechanisms play a crucial role in this unloading procedure. The goal of this study is to analyse and describe this unloading process. An attempt is made to model the processes in such a way that an estimation can be made for the unloading time. During this research two sets of experiments were executed, the preliminary and the main experiments, each with a different experiment set-up, to obtain more insight in the unloading process. The goal of both sets of experiments was to get a two dimensional view on the sand-water-processes above the discharge opening. The most important parameters which are varied during the experiments are the width of the discharge opening (wdo) and the height of the sand at the start of the unloading process. Out of the preliminary and main experiment comes the qualitative description of the unloading process in time: 1. Coming into existence of a dome. 2. The failure of the dome. 3. Fluidization of sand mass. 4. Break through of water through the sand-water mixture 5. Breaching of sand from the walls at both sides of the discharge opening. For two components out of the unloading process a first set-up for a quantitative model is made with as final goal a good prediction of the total unloading time of a barge. These two components are: 1. The dome that comes into existence 2. The moment of failure of the dome With the theory in this thesis and the data of the executed experiments can be concluded: Total unloading time: o The total unloading time decreases for an increasing width of the discharge opening Expanding velocities: o A new approach has been developed for the single particle mode in which the perpendicular expanding velocity for the roof of the dome (?=180 degrees) is approximately 2.2 times larger than expanding velocity perpendicular to the vertical walls (?=90 degrees). This new approach fits a lot better with the data out of the experiments for the expanding velocities of the dome, but is not yet completely satisfying.

saturated sand
dredging
unloading process
discharge opening
water jets

http://resolver.tudelft.nl/uuid:1fca2eee-5e1f-4e28-99aa-f13c035e6442

Student theses

master thesis

(c) 2009 Van Aalderen, M.W.