A4ALL consortium consisting of Boskalis, Heijmans and Volker Wessels, was commissioned by Rijkswaterstaat for the design and construction of the A4 Middle Delfland highway project between Delft and Schiedam. The 7km highway Consists of an approximately 4 kms (half) deepend part and a (on) land-tunnel for another 2 kms.
CRUX Engineering has, as a member of the design team at A4ALL, contributed to the design of the landtunnel, the (half) deepened location and structures at Kethelplein where the A4 meets the A20 and the existing part of the A4. The realization of the construction of the various parts started in 2013. Since then, CRUX has also performed part of the site-engineering. In approximately 3 months, 3200 Vibro piles have been driven by piling rigs for the land-tunnel. Meanwhile, after one year of construction, the concrete work of the land-tunnel is almost completed.
The road within the deepened part of the route, is constructed 12 meters below ground level. This part will be constructed using cement-bentonite walls inside an artificial polder, in order to construct the road at this level and minimize environmental impact.
The land-tunnel is built at ground level and is completely covered with soil. At a number of relevant locations of this embankment, additional bending moments in the piles of adjacent structures, as a result of (horizontal) ground deformations, have been determined . These ground deformations occur, among others, at the location where the land-tunnel transitions into the structure on the underlying Laan van Bolés. The ground embankment, which is applied against the land-tunnel, is ended vertically using a retaining wall on stilts. The moments in both piles of the retaining wall, as well as the piles under the abutment of the connecting structure are determined by using PLAXIS 3D. After performing the 3D reflection for the headwall, the design was adapted to a more economical design where fewer (ground) deformations occur.