GEOTEXTILE TUBE APPLICATION AS THE COFFERDAM AT THE FORESHORE WITH LARGE TIDAL RANGE FOR INCHEON BRIDGE PROJECT

摘要

Design details and construction procedures of the large-scale geotextile tube works as the cofferdam of the temporary access road for Incheon Bridge constructions are introduced. 18.25 km long sea-crossing lncheon Bridge connects Incheon International Airport with the international free economic zone at New Songdo City in Incehon.Construction site is a foreshore which the tidal range is up to 9.27 m and the subsurface consists of soft silty clayey soil.There were so many difficulties in installation of the geotextile tube on the soft tidal flat due to huge differences in the water level between ebb and flow. The diameter of polyethylene tube is 4 m, or 5 m and the length of each tube is 50 m.Sands were used as a filling material instead of dredges soils which was originally planed to fill the tube. Hydraulic pumping of sand mixed water to the tube through multiple injection ports gave advantages to reduce the construction time and to maximize the tube size after the injection completion. Two sets of the 4 m diameter tubes were installed on the ground surface and 3 tubes of 5 m diameter were stacked on these tubes in sequence. Special featured sand filled fabric forms were spread at each stacked layer to increase the friction between the tube surfaces. Polyester geotextile mat was used as a scour protection apron and post piles fixed the mat to the ground. Various kinds of offshore equipment including flat barges were used and working schedule was planned according to the information of tidal range. Instrumentations have been also performed to monitor the behavior of the geotextile tube.