Reconstruction of Rijnlandroute N206

Situation

Reconstruction of a busy regional road connecting the area on the west coast (North Sea beach) to the A4 motorway. This link is called the Rijnlandroute and consists of several sections, including road widening and the construction of a tunnel near the city of Leiden. It is located next to a suburban area. The traffic causes road noise and blocks the beautiful view of the green areas next to the suburban houses. For this reason, this section of the road was lowered by means of a so-called ‘polder construction’. The N206 road was deepened using a waterproof geomembrane layer to prevent groundwater infiltration. The project was carried out by main contractor Boskalis Infra Nederland. During the tendering phase, HUESKER worked closely with Boskalis to investigate the feasibility of an innovate way to retaining the soil in the most economical way. The final design consist of a geogrid-reinforced earth wall that retains not only the soil, but also the lateral loads from the water table. This combination of retaining lateral loads from the vertically installed geomembrane against the earth wall is innovative and has not been implemented before.

Solution

An MSEW wall with PVA geogrid was used for economic reasons. The alternative is a watertight concrete structure with permanent sheet piling. Another important aspect is that the MSEW with PVA Fortrac geogrids allows the use of soil and asphalt fill that was released during the demolition phase of the old road. The fill of the MSEW therefore consists of a layer of mixed asphalt granulate and a layer of recycled granulate. In addition, the green wall facing of impregnated wood planks looks very nice and will look even better when the plants on the tow are fully grown.

Efforts

It is also worth mentioning that Huesker supported the main contractor Boskalis during the tendering phase to win this tender design. Thanks to our efforts, the authorities accepted this innovative design with MSEW. HUESKER supported the Boskalis design team to complete the very complex design activities, including stability analysis, deformation analysis and complex installation drawings. This phase took more than 1.5 years! No cross section was the same, it was different all the way through.