Since 2020, BESIX and its partners have been working on the Toots Thielemans metro station, right in the heart of vibrant Brussels. This project plays a pivotal role in the future Line 3 of the Brussels metro system, a crucial endeavour aimed at knitting together the city's centre, north-east, and south-west.
So, what's cooking beneath the boulevards of Brussels?
Our mission includes the construction of two tunnels, stretching 300 metres and 210 metres, as well as a 233-metre-long metro station.
After a few challenging hiccups that temporarily paused the project, we're thrilled to report that our on-site team is back, having reached a crucial turning point.
The excavation work for the first underground level, housing the 300-metre-long tunnel under Boulevard Jamar and the metro station, is officially wrapped up. In the coming months, they’ll be diving into structural reinforced concrete work, crafting slabs, beams, and walls that'll soon define the underground station's character. Then, it's on to the next underground level. Meanwhile, on the surface, they’re already working on roadworks to return part of the construction site area back to the public space.
But what's our secret sauce to juggle surface and underground work without causing chaos?
Introducing the Stross Method
As the future station is nestled in a densely populated area, we were determined to minimise disruptions and sidestep the pains of year-long open pits. Enter the Stross method, an integral part of the cut-and-cover approach that's our trusted ally in such complex settings. The cut-and-cover method is often applied in Belgium for relatively shallow structures, where tunnel boring machines can't be utilised, or open pits want to be avoided.
Here's how it unfolds:
- The 'Cut' Phase: We start by crafting outer underground walls and foundations from the surface, employing deep foundation techniques like slurry walls. This phase, aptly named 'cut,' was sealed in October 2022.
- The 'Cover' Phase: We build the roof slab on top of these walls and foundations. The concrete slab is expertly poured onto the ground after a limited excavation from ground level. This 'cover' phase got its stamp of completion in May 2023.
- The 'Stross' Phase: Now that the cover phase is behind us, we dive into the 'Stross' phase. This is where the real magic happens as we excavate beneath the roof slab and gradually mold inner structures like slabs on various underground levels, stairs, shafts, and bottom slabs. We ferry the necessary materials underground through temporary openings in the roof slab, using specialised cranes positioned above-ground along the tunnel and future station.
The cut-and-cover method isn't just any method. It's a game-changer, especially in projects like Toots Thielemans. Why? It keeps construction pits out of the picture, keeping disruptions to a minimum for our neighbours and streamlining the creation of complex underground structures. Plus, it lets us work on both levels simultaneously, making it super-efficient.
Some of our readers might recall that this method was also used during the realisation of the Neuilly-Sur-Seine hospital complex in France. Building top-down enabled us to significantly reduce the construction time on the project and maximise space on the very constrained site.
Hats off to our colleagues working relentlessly on this project, and here's to continued success as we delve deeper into this underground masterpiece.