References
Oxygene tower, Lyon
FRANCE, 2007 2008
The 115m high Tour Oxygène building backs on to the Part Dieu shopping centre in the heart of the business quarter of Lyon.
The 115m high Tour Oxygène building backs on to the Part Dieu shopping centre in the heart of the business quarter of Lyon. A second building, the Cours Oxygène, links the Tour Oxygène with the shopping centre and forming an extension to it. The site also includes four levels of underground parking. Solétanche Bachy was appointed as the specialist foundations subcontractor. The site is located in an extremely densely populated area where access is difficult: the site is close to bus, tramway and trolleybus routes; access is by the Bonnel open cut with a height limit of 4.10m. A single access served for both site ingress and egress. In addition, working space was limited since there was little available area outside the confines of the 5000m2 site. Furthermore, the site is located in the immediate vicinity of sensitive shared boundaries: the La Part Dieu shopping centre on the South and West (at a distance of 30cm), the Brotteaux Servient open cut to the East (at a distance of 20cm) and the Bonnel open cut to the North. Below ground, the metro B line is only a few tens of metres away. Preliminary works such as a campaign of percussive investigation, grouting, the demolition of a technical gallery and overhanging foundation had to be carried out. The diaphragm wall and barrette works were then carried out with two KS2 hydraulic grabs.
The diaphragm wall
Outside the area of the tower the wall was constructed to a depth of 27m. In this area the reinforcement was discontinued at a depth of 21m with the remaining 6m being required for the hydraulic cut off In the tower area, the reinforcement was continued to the bottom of the wall (27 or 30m). The cut-off level of the diaphragm wall was -2.10m for the area outside the tower and -3.25m for the tower zone. The water table is -1m below working platform level.
The barrettes
The barrettes were installed under a certain number of constraints: a very congested layout, low cut-off (-15m), different lengths (2.8m to 10m) and thicknesses (820mm and 1020mm). In addition, the working platform was close to the water table.
Ground Anchors
In general, the diaphragm walls were stabilised by 2 levels of temporary ground anchors though the curved section was designed as an arch and salient corners were stabilised by oblique struts. The ground anchors wre installed through blow out preventers.
Techniques
A diaphragm wall is a reinforced concrete wall that is made in situ. The trench is prevented from collapsing during excavation, reinforcing and casting by the use of supporting bentonite slurry. The slurry forms a thick deposit (the cake) on the walls of the trench which balances the inward hydraulic forces and prevents water flow into the trench. A slurry made of polymers can also be used.
A ground anchor is a load transfer system designed to transfer the forces applied to it to a competent stratum. An anchor is said to be temporary if it has a lifespan of under two years and permanent if the lifespan is over two years.
Ouvrages
Suitable foundations are required for all building and civil engineering structures to ensure that they perform within the settlement criteria established in the design of the structure. Special foundations are used where shallow footings do not provide adequate support for a structure.
Major urban excavations are one of the specialist activities of Soletanche Bachy. Such excavations are required for basements to buildings that are usually part of the foundations of the structure and also used for under-street car parks, cut and cover tunnels for roads, rail, metro and storm water tank...
Voyage au coeur de l'ingénierie de pointe
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