Reconstruction N206 ir. G. Tjalmaweg

Reconstruction N206 ir. G. Tjalmaweg

The provincie Zuid Holland intends to improve the accessibility of the Holland-Rijnland region (between Amsterdam and The Hague / Rotterdam). Contractor Boskalis has been tasked to upgrade the existing N206 Ir. G. Tjalmaweg, from design to realization. The improved N206 will have 2 x 2 lanes between the junction Leiden-West and the connection to the N441, and will largely be constructed below surface level. There will be two split-level intersections connecting the N206 to lolcal roads. The sunken highway is constructed by means of a polymer geomembrane construction in combination with reinforced ground constructions forming the walls on both sides.

Irregular geology

In the vicinity of N206 the Holocene deposits in the subsurface consists of very irregular layers of clay and sand, which is caused by a complex dynamic between the tidal influences of the North Sea near the mouth of the Oude Rijn in the last 10.000 years.

From a modest contribution in the tender, to a wide variety of geotechnical solutions for the final design

Arthe Civil & Structure has been approached by Boskalis during the tender for the project N206 Ir. G. Tjalmaweg. Arthe had provided the geotechnical design of the embankments: predominately settlement and stability calculations of the embankments and reinforced soil structures.

During the preliminary design and final design phases, Arthe’s involvement has been extended to the geotechnical design of:

• A polymer geomembrane construction which is an essential part of the sunken highway;
• The temporary sheet piling including anchors to create a construction pit to realize the sunken highway;
• Gel permeation grouting to obstruct the groundwater in the construction pit;
• Permanent sheet pile wall guaranteeing the stability of the reinforced soil structure and the canal
• Shallow foundation for three culvert bridges;
• The foundation for portals (both shallow and on piles)
• A construction founded on reinforced soil
• Embankments that serve as the entrance and exit roads of the N206;
• Wooden banking close to the roundabout with the Torenvlietslaan.