Stabilization of Precuts on the Trimberg Tunnel

Context

With the new, 4-lane motorway section A44 between Kassel and Herleshausen, the gap between the A44 Dortmund-Eisenach and the A4 near Eisenach will be closed and an important East-West connection created in Germany. The project includes the construction of the Trimberg Tunnel, a tunnel structure with 2 parallel, 600m long tubes that are connected via 2 crosscuts. The 440m tunnel tubes are being built using underground excavation.

Solution

The precuts (East and West) that were realized on both sides of the Trimberg Tunnel were stabilized using Gewi Soil Nails. Afterwards, 4,000m³ of double reinforced shotcrete were installed over the precuts.

The soil in the precut area consists of slope loam and silt in the first two thirds above the groundwater table with consequent mixed-grained soil and rock pockets. From the groundwater table onwards, the soil is increasingly solid with prevailing sandstone. In the water sensitive slope loam, flushing was at first not permitted during drilling when installing the Gewi Soil Nails. After comprehensive drilling trials, the required wet drilling method was established in co-operation with the Owner following strict requirements.

The technical challenge consisted in sealing and grouting the up to 30m long soil nails that ascended up to 2°. The soil nails that were inclined at 20° had to be grouted up to a length of 26m using pressure injection.

All of the products supplied by DYWIDAG were especially tailored for use on this jobsite in order to ensure an optimum handling and assembly of the Gewi Soil Nails with a minimum effort to the required lengths of 8 to 30m.

Approx. 40,000m of temporary 32mm Ø Gewi Soil Nails and approx. 50,000m of permanent 32mm Ø Gewi Soil Nails were installed to stabilize the precuts.