GENEVA'S LATEST weapon in the battle against congestion is a six-level car park built 3m beneath Lake Geneva.
The 900 space car park is being built under a marina to provide easy parking for traffic approaching from the east along the shore.
A joint venture of German contractor Bauer Spezialtiefbau and Swiss firm Perrin Freres carried out the extremely complex foundation work for client Fondation des Parkings Geneve.
First step was to enclose the marina within a square sheet pile cofferdam. Water was pumped out and an embankment built inside to provide a working platform for installing the 36m deep, 1m thick diaphragm wall forming the permanent car park structure.
Bauer used a hydraulic grab to socket the 8,500m 2of diaphragm walls into the underlying rock-like molasse formation. Excavations were complicated by a layer of gravel with high artesian water pressure, which was controlled using a heavy slurry.
Bauer's contract included installation of anchors, groundwater control and sheet piling for the entrance ramps.
The finished diaphragm walls were propped by four rows of struts which were removed as the car park's internal structure was built.
On completion, the cofferdam will be removed and the marina restored.