First bascule cellar successfully sunk

The counterweights of the two new bridges over the Amstel River at Ouderkerk will soon be located neatly below the waterline in two bascule cellars. These basements will be built on the bank and then retracted and jacked using an ingenious method developed by Civil Engineering deBoer. The first cellar has already been successfully sunk.

"Back in 2018, we were approached by Van Hattum en Blankevoort to work out a plan for retracting and jacking both bascule cellars," says Paul den Hollander of Civil Engineering deBoer. "At 220 tons, the basements are too heavy to hoist in with a traditional crane. Because of the limited lead time, the whole operation had to take place in one weekend, we came up with a combined construction. That way we can do a double stroke in one pass: retracting and subsequent jacking."

To ensure the necessary stability and bearing capacity, Ct deBoer's slideways rested on a previously installed auxiliary structure of piles, sheet piling and brackets. "At the moment suprême, the concrete basement box was lifted over onto the sliding tracks via cast-in-place lugs in order to then slide the colossus up some 20 meters across the water," explains Den Hollander. "In that same corridor, the basement was jacked off and laid down on its final piles, 4 meters below the waterline. And all that in the space of just two days, including the erection and dismantling of our auxiliary structures, jacks and hydraulic pump units." At the end of the summer, Ct deBoer will repeat this "trick" again for the second bascule basement.