Abstract:

Honggu Tunnel in Nanchang is an immersed tunnel located in middle reach of Ganjiang River, where the flow velocity drop and water level drop are large. There are great difficulties in largescale cofferdam construction, segment prefabrication in two docks, segment floating transportation and docking and tunnel foundation treatment effect detection. As a result, a series of technologies are adopted. The technologies adopted include: 1) The complex structure of gravel filled tubular pocket + plastic concrete wall + reinforced concrete wall and dry out method for steel tube plug pile in foundation pit are adopted so as to realize rapid construction and flood prevention and antipermeability of the cofferdam. 2) The segment prefabrication quality and efficiency can be guaranteed by technologies used for mixing proportion design, casting, curing and temperature control of concrete, key equipments selection for segment prefabrication and replacing method for largescale steel mold. 3) The safe longdistance segment floating transportation can be guaranteed by using professional equipments, rational tugboats formation and multifunctional GPSRTK monitoring system. 4) The accurate docking of segments under high water level drop is realized by using visualized monitoring system, submarine survey work and watertightness control technologies for the connection between joints. 5) The realtime monitoring and comprehensive evaluation of gravel filling effect of tunnel foundation are carried out by using impact imaging method and underwater inspection method. The construction practice shows that the technologies adopted are rational and highefficient; and can reduce risks and the cost and shorten the construction period.

Key words: immersed tunnel, cofferdam construction, segment prefabrication, segment floating transportation, segment sinking and docking, foundation treatment