Construction pit for tunnels around N421 bypass

The N421 was constructed in 2015 to enable a connection between the A12 motorway and Houten. This road crosses the Parallelweg (Structure 1) and the Achterdijk (Structure 3). To ensure smooth traffic flow, tunnels were built under the N421 for both roads. Genap was tasked with applying a geomembrane construction to create a construction pit.

For Structure 1, a Genaflex PVC 1 mm geomembrane of approximately 4,500 m2 was sunk between steel sheet piles. Geotextile was applied at the location of the steel sheet piles to protect the geomembrane. For the construction of the construction pit for Structure 3, Achterdijk, we used a combination of Genatex Geotextile 500 gr and a groundwater-retaining geomembrane construction, Aquatex PVC 1 mm, placed based on its own weight. The total construction extends over approximately 185 meters in length and 25 meters in width, between the final steel sheet piles.