References
Carrefour Romarin - La Madeleine
FRANCE, 2006
Sensitive geotechnical works for the Grand Boulevard roadway drop.
The Romarin district in La Madeleine city has always been crossed by the “Grand Boulevard” (familiarly known as “the mini tunnels”), a major route through the Lille town (41,000 vehicles each day), doubled by a tramway route (32,000 passengers each day) linking Lille to Roubaix and Tourcoing.
As part of this district’s rapid development, we were asked by the Lille Métropole Communauté Urbaine to undertake works for lowering the Grand Boulevard, the first stage in the construction of the “Place du Romarin” which will link both banks of this district.
This drop in level consists in constructing two parallel diaphragm walls, each measuring 200 linear metres (at depths of between 9 and 16m, and measuring 600 and 800mm wide), a roof bearing on these walls and which will form the new square, 33 temporary ground anchors, underpass excavation and then “blind” excavation below the slab, and, finally building the road network.
Constraints and methods
The major constraint affecting this project was the timescale: 1 month for preparation and 4 months traffic closure of which 1 month was allocated to carrying out all diaphragm wall works. In order to meet this deadline, we mobilized up to 3 cable grabs and 3 handling cranes, in two shifts, on the boulevard. Between two and three concrete panels were cast every day.
Proximity to the tramway catenaries, the confined nature of the site and on-going simultaneous activities made site safety a priority. The project was completed without the occurrence of any accidents.
The pedestrian walkway straddling the Grand Boulevard was retained and remained operational throughout the project. Micropiles were used to underpin this walkway.
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.
A pile is a structural element driven into the soil for transferring loads and prevent deformation. Its slenderness ratio is not limited.
Pile shafts can be uniform and rectilinear, telescopic and belled out.
Piles can be installed either separately or in groups. They can also form a retaining wall, a mixed curtain wall, contiguous piles, secant piles and composite curtain walls, such as Berlin walls and similar. Piles are also used as precast beams to be placed in the structure of the building they support.
Ouvrages
Soletanche Bachy has developed a number of techniques for use in road structures; cut and cover tunnels, viaduct etc.
Voyage au coeur de l'ingénierie de pointe
Find out more about our expertise by:
