In the coming weeks, construction will once again be seen at Lezennes Station. In fact, work never actually stopped, but had to go back to the engineering consulting office. After the first phase of underground construction and reinforcement, building operations are returning to the surface in order to create two new points of access to the platform.
The 52 meters passage at Lezennes Station requires the opening of two new additional access points, as is the case for many other stations. Since the Lille metro became operational, the legislation has evolved. It is now necessary to have two emergency exits for each platform, and escalators are not considered acceptable for emergencies.
However, before the first pickaxe strike, it was necessary to know the exact routes of the numerous cables and pipes that run under our feet such as water, gas, electricity, telephones and more. They are often grouped together close to the sidewalks in order to facilitate interventions without completely blocking the flow of traffic.
The opening of new metro exits on either side of the Roger Salengro Roadway means that the cable and pipe networks will need to be moved more towards the center of the street. Examination of the first plans and surveys of the street left no doubt: the European Métropole of Lille (Métropole Européenne de Lille) had to ask distributors to move their networks. This operation lasted several months. It required decreasing the traffic in one direction, while maintaining alternative routes for both pedestrian and vehicular traffic—the only solution to avoid completely shutting down the road.
After the completion of this first step, excavation for the new exits was scheduled to begin. However, before cutting into the slab that covers the station, Norpac, the company in charge of construction, proceeded with surveys to measure the resistance of the rock. The engineers estimated that the available plans didn’t provide precise information on the reinforcement of the concrete slab (the plans dated from the construction of the station, in the 1970’s). Three months were necessary to get more accurate measurements on the slab. The result? The slab had to be reinforced before cutting it and making new openings. The engineers therefore conducted complementary studies and developed a solution.
Norpac will elevate four support posts around each funnel opening. This technique presents no particular difficulties. The subterranean work will take place within an enclosed space inside the station and will take place during daytime. At the end of June, a construction train brought the necessary materials for the creation of the pillars: rebar and metal beams. The company will install a small concrete mixing plant close to the building site.
When the reinforcement columns are finished, dry and ready for use, the drilling operations can start: cutting into the slab with a suitable saw, molding the structure of the stairs…Construction operations will then, finally, be moved to the surface, in a consecutive way. This will allow the street to be only half occupied each time in order to maintain alternated traffic. The entirety of the work will last several weeks. This long project will finish with the restoration of the sidewalks.
Are you surprised by the complexities involved in the construction and engineering process? Does further insight increase your appreciation for the infrastructure in your city?
Original article, originally published in French here.
Credits: Data and images linked to sources.