About The Project
Aalst is a Flemish town of 83,000 inhabitants situated 25 km northwest of Brussels. The city recently finished the redevelopment of the Hopmark square and surroundings, one of the big projects the municipal council has launched to renovate its historical city center. The project involves the construction of a three level underground car park for 317 cars and the reconstruction of the square with trees and an area for public events with two pavilions housing a bar, a restaurant, a city shop and parking utilities. The construction of the car park, the pavilions and the area for public events was awarded to Interparking NV, who will run the car park in concession for 30 years. Interparking contracted MBG NV for the construction works. The Hopmarkt square is surrounded by buildings without deep foundations. Due to a settlement risk on a subsoil of peat layers and soft loam, the construction work had to be vibration free (< 2 mm/s) and lowering the water table was limited. The lowest water level allowed outside the building pit was -4.5 m below street level (8.5 m TAW). Therefore, the original design included an execution with slurry walls, reaching into the clay layer up to -20.0 m below street level.
Soil & piling contractor Soetaert-
Soiltech proposed a more economical
and faster solution with a better
watertightness: a combination of
Cutter Soil Mix (CSM) and steel sheet
piles. Sheet piles can be lowered in
fresh soil mix walls without generating
any vibrations. After hardening, the soil
mix walls serve as a watertight screen
during excavation (kh
< 10-8 m/s).
The sheet piles act as retaining walls
during and after the construction
phase, as 100% watertight walls after
excavation, and as permanent visible
walls after completion of the car park
transferring vertical loads from the car
park (acting like bearing piles).