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The City of Luxembourg is currently building a wastewater drainage system connecting the water treatment plants in Bonnevoie and Beggen. The works owner – the Service Canalisation (Sewer Department) – will undertake this work together with various internal and external service providers.
The total length of the piping system will be 6,150 metres, and the average depth will be 10–15 metres. A reinforced concrete pipe of DN 2,000 mm and internal protection with PE coating will be used. There will be nine access points to the site. Installation will be carried out through underground passages.
Commencement of work: February 2012
Planned completion: end of 2020
Why do we need new drains?
Following the introduction of new European directives in the early 1990s, Luxembourg City faced the following choice: either the Bonnevoie water treatment plant had to be upgraded to be able to treat nitrogen as well, or the plant had to be connected to the Beggen water treatment plant, resulting in the permanent shut-down of the Bonnevoie plant.
Following a technical and financial study, Luxembourg City opted for the latter alternative. This led to the idea of drains to transport waste water from the capital's southern neighbourhoods (Bonnevoie, Cents, Hamm, Pulvermühl and Gasperich) to the Beggen water treatment plant. This would also make it possible to collect water from Luxembourg City's other neighbourhoods and thus take the load off the existing drains.
There are further advantages still. A collector of this kind can also serve as a water retention basin and thus regulate the flow of water into the Beggen plant, or as an emergency basin in the event of a breakdown at the plant.
A few important dates
As with all of Luxembourg City's major construction projects, the project to build the drains connecting the Bonnevoie and Beggen water treatment plants had to go through several stages before construction actually began:
1993: technical and financial study on combining the two water treatment plants.
16 October 2002: the municipal council votes in favour of the draft proposal.
6 May 2004: the Chamber of Deputies votes in favour (Law of 6 May 2004).
26 June 2006: the municipal council votes in favour of the final plan. Applications for authorisation (Services Voirie, Eau, Environnement, CFL, "commodo" operating permit, etc.) Agreements with property owners.
Studies (project, hydraulic, risk, geology, insurance, materials, etc.)
9 December 2009: outcome of the bidding process is announced. Legal appeal against the decision.
9 January 2012: work begins.
2015: Temporary pumping station in the Pétrusse begins feeding water to the Beggen water treatment plant.
2020: Civil engineering works completed by the end of the year; new wastewater drainage system fully operational, feeding water from Bonnevoie to Beggen; temporary pumping station dismantled.
Work has been done in parallel in different locations. This has allowed us to make rapid progress, optimise the use of our financial and human resources, and minimise disruption to residents and visitors.
Main work-site challenge: sheer size of the project
Building such a huge drain network is an extraordinary, technical challenge. How can over six kilometres of pipes be built in the heart of the capital? What construction method should be used to ensure minimum disruption and maximum efficiency? What equipment should be used for the job?
Selection of a route
During the planning stage, our Service Canalisation considered a number of different factors, such as how the current water treatment plants operate and the connection points of the existing drains.
Other criteria, such as respect for private property, also played a role. The route that was finally chosen prioritises the use of public land and property, avoids disturbing vehicular traffic to the extent possible, and takes the geology of the terrain into account.
Pipe jacking and construction principles
Drains located at great depth are installed by underground pipe jacking (Unterirdischer Rohrvortrieb). This means that over the 6.15 km, the site's teams dig nine trenches. These trenches are approximately 15 metres deep, and 10–15 metres in diameter. They are secured by concrete piles along their sides, and then excavated.
The pipe jacking machine is set up inside the trenches and digs the tunnels into which the reinforced concrete pipes, with an internal diameter of 2 metres, are installed.
Progress to date
As the teams are working at several access points simultaneously, progress varies from one site to the next.
No. 1: Works to install the inspection chamber for the trench at the Bonnevoie water treatment facility are completed.
No. 3: The third trench is located in the Pétrusse Valley at "Schlittenhiwwel". The trench is complete. The temporary pumping station currently pumps water from the Bonnevoie water treatment plant to Beggen, to treat water from the Bonnevoie sewer lines at the Beggen plant even before the main collector is complete. The pumping station will be taken offline and dismantled by the end of the year. Final trench completion works will then be undertaken.
No. 4: Completion of all works on trench no. 4 and final improvement works in the square.
No. 5: Trench No. 5 is located on Rue Laurent Ménager near the Gaston Diderich Stadium. Works completed.
No. 6: In Rue Munschen Tesch, the contractor is currently undertaking temporary completion works. Local improvement works will be undertaken at a future date by the City's Service Voirie (Roads Department).
No. 7: The work is complete.
Nos. 8/9/10: The trenches on Rue Pierre-Joseph Redouté (No. 8), on Rue de Bastogne (No. 9) and at the Beggen water treatment plant (No. 10) are complete. The section of the drain network joining these three trenches is also complete.
Pipes have been lain between Beggen and Bonnevoie.
Work to install the required electromechanical equipment in all trenches is currently under way. Since the drainage system will form an integral part of the Beggen water treatment facility, all the trenches will connect to that plant to better facilitate the monitoring, checking and regulation of the wastewater.
Contacts for this work site
VDL – Service Canalisation
VDL – Construction Mediators