A46 federal motorway between Bestwig junction and Nuttlar

In the course of construction work to replace a section of the A46 federal motorway between Velmede and Nuttlar, engineers cut into the side of the Sengenberg, a mountain adjacent to the carriageway, for around 800m. The resulting embankment had to be secured using an anchored jetcrete lining fronted by a gabion wall along the entire section. The project used the Stump soil nailing system, which has been given a general technical approval by the German building authorities.

The maximum height of the embankment stabilisation system is 24.50m. The cuts into the slope were excavated in 5m-high steps. This meant that, at its highest point, the stabilisation project involved cutting five steps, with partial excavation required for each level.

The embankments were implemented at an 80° angle and with three rows of two corrosion-protected durable rock nails, most of which were between 8m and 12m long.

A 20cm-thick reinforced jetcrete lining was applied to the embankments to protect the rock against weathering and prevent it coming loose, and also to protect the nail heads against corrosion.

Pressure relief holes were also drilled in the jetcrete lining to prevent the build-up of pressing water behind the lining. These perforations were drilled in a 1.00m x 1.00m grid. The precipitation water seeping onto the berms will be collected in 5m-long drainage boreholes. In addition, the embankments feature 35m-long drainage boreholes at horizontal intervals of 10m in order to lower the water table in the slope.

One of the most significant challenges in linear construction sites such as this is the logistics of material movements and ensuring access routes to the site. Due to the constant earthworks and removal of rubble from the site, new access routes had to be set up on numerous occasions.