THE COPENHAGEN METRO CIRCLE LINE-TUNNELLING AND STATION CONSTRUCTION CHALLENGES IN URBAN CONDITIONS

摘要

The paper will describe challenges for design and construction of the tunnels and stations in soft ground conditions in an urban environment for the Copenhagen Metro Circle Line. The project consists of 15.5 km metro line with 17 underground stations. The ground conditions are 10–15 m of glacial deposits overlying a limestone, which are fissured and include hard layers of flint. The stations will be constructed as Cut & Cover structures using top-down construction technique and retained within a station box of either secant piles or diaphragm walls. The tunnels located in the glacial deposits and in the limestone will be constructed using closed face TBM’s of either EPB or slurry type. As many of the old buildings in Copenhagen are founded on wooden piles which will deteriorate if exposed to oxygen, there are requirements for not lowering the groundwater table. One of the major challenges for the project is to control the groundwater during tunnel and station construction. A system of combined dewatering and recharge of groundwater in places in combination with grouting will be utilised. The paper describes the challenges in selection of construction methods dealing with the strict requirements for groundwater control, noise and vibrations and settlement control. The project is tendered as a design and construct project during summer/autumn 2010 and construction contract signed in January 2011.