Extreme long geotubes.
Type:
Presented during:
CEDA Dredging Days 2005 - Dredging: The Extremes, Rotterdam
Authors:
Zijl P.M.N. van, Vlasblom W.J., Gijt J.G. de, Broos E.J. and Boer J. de
Abstract: For several years geotextile-tubes (geotubes) have been applied in hydraulic and coastal engineering such as shore protection and breakwaters. With the present techniques it is not possible to apply geotubes in rough and relative deep water. In 2002 the CUR committee C129 presented a report that describes the expected problems in the concept device to fabricate a continuous geotube that can be used in open sea conditions. The main problems in the concept were:
-
Integration between sewing of the geotextile and filling of the tube with sand.
-
Stresses in the geotextile and a clamp system to transfer the forces to the pontoon
A master study was started at the Delft University of Technology to investigate these problems more in detail and if solutions were possible, To guarantee a constant production speed and a high-quality final product the geotextile tube is pre fabricated. The tube is folded to a compact package with an opening in the centre. Filling of the tube is now possible through this opening. The geotube is lowered vertical to the seabed and the height of the sand in the tube above the seabed (fill height) is kept constant. This results in a constant shape of the geotube on the seabed. To understand the static stresses acting in the geotextile, two mathematical models were made for calculating the stresses during and after placing on the seabed. The main simplification in the models is that the geotube is filled with a fluid of the same density as sand. Scale tests showed that a simple clamp system fixing the geotube on 40% of the circumference could transfer up to 75% of the total axial strength of the geotube. Finally a conceptual design was proposed for filling and placing the continuous geotube on the seabed.
Keywords: Geotextile, continues geotubes, dredging