No more water in the pit of Garenmarkt

10 January 2019

The story...

Construction of the underground parking Garenmarkt in Leiden, The Netherlands.

Hurray, we reached a milestone: the pit is water-free!

Hold on, an underground parking is not supposed to be drained first? Yes and no. OK, 55.000m³ of soil was pumped liquid from the pit to a location outside the center by boat. Mind you, this saved 60 trucks of daily traffic! However, water from the neighbouring ‘grachten’ (canals) was simultaneously pumped back into the pit.

Huh. Why bother filling the pit with water & then drying it up again?

Because extracting that amount of sand without providing reinforcement could have caused the pit to crumble down like a house of cards. Thus, it was filled with water to keep sufficient pressure on the (deep) wall panels during excavation.

Hold on. You mean they did part of the job under water?

Yes indeed! First, the deep walls "outer shell" were made in the ground by Franki Grondtechnieken. Then the teams literally "dived in" and started, after a series of preparatory works, pouring underwater concrete: two concrete pumps unloaded a staggering 3.800 m³ of concrete to create the floor of the garage.

And water was the only solution to keep the entire framework secure?

Not really. As they gradually dug deeper, various measures were taken to make sure the pit retained its shape and didn't turn into a Barbapapa. From introducing a concrete punch frame to support the deep walls at the top to lowering the steel frame halfway to absorb the forces that came up during excavation. They even installed freezing pipes between the deep walls and concrete floor to freeze the seam between these, avoiding possible leaks after emptying the construction pit.

So now it’s waterproof?

Yes, the concrete slab has now been put in place, which means water pressure is no longer necessary: 40 million litres of water has been pumped out.

Next steps?

The Combination BESIX and Dura-Vermeer is currently pouring the final concrete floor, after which they will start building the underground parking. The garage will consist of 5 floors and provide space for 425 cars.

Fun fact: archeological discoveries

Did you know archeologists searched the site for remains during five weeks? And successfully! They found remains of a 1960s textile factory, of walls from XV & XVI century houses, and even of pits from Roman times!

Construction parking Garenmarkt BESIX
Underground parking Garenmarkt Leiden, Nederland. © Buro JP.
Construction parking Garenmarkt BESIX
Underground parking Garenmarkt Leiden, Nederland. © Buro JP.
Construction parking Garenmarkt BESIX
Underground parking Garenmarkt Leiden, Nederland. © Buro JP.