Clean Material Separation: Breaking out the Temporary Top Heading Invert in the Trimberg Tunnel
During the excavation the Trimberg Tunnel for the new motorway A44 Kassel – Herleshausen in Germany, the tunnellers encountered difficult geology and had to install a temporary top heading invert of shotcrete. To break out the invert, a Kemroc DMW 130 cutter wheel mounted on a 23 t excavator was used. The shotcrete was cleanly separated from the ground below and recycled as a valuable construction material.
Numerous structures make the new building of the motorway A44, a link between the motorways A7 at Kassel and the A4 at Herleshausen in a west-east direction, a challenging infrastructure project. These include the two tubes of the 600 m long Trimberg Tunnel, which was started in 2016 and is mostly being mined. In both tubes of the tunnel, the miners from the joint venture Hochtief/Züblin are faced with difficult geological conditions: settlement and loosened rock occur along a length of 250 m in the Bunter sandstone. Therefore the client DEGES provided a temporary top heading invert of shotcrete. At the start of April 2019, the north tube of the Trimberg Tunnel was broken through and the miners started cutting out the invert with a cutter wheel.
Clean Cuts through Rock and Concrete
Kemroc cutter wheels of the Series DMW with double motor are produced in four sizes for excavators from 14 to 60 t working load. Two side-mounted, high-torque hydraulic motors ensure high drive power and cutting force, so the machines can develop high cutting performance even in hard rock and heavily reinforced concrete. The manufacturer offers various cutter wheel variants for cutting depths of up to 1000 mm and various tool fitments up to 400 mm wide.
For the breaking out project in the Trimberg Tunnel, a cutter wheel of type DMW 130_600_130 (nominal power 130 kW) with 130 mm cutting width and 600 mm depth was chosen. This was able to achieve a remarkable cutting performance of 15–20 m/h. At the start of the breaking out process, the excavator driver cuts a piece about 2 x 2 m out of the shotcrete. This is then broken out of the rock below with a wheeled loader or excavator, loaded onto a tunnel dumper and transported to the processing plant at the portal, where it is processed as recycling material by the disposal firm.
In autumn 2019, the breaking out of the temporary invert in the north tube of the Trimberg Tunnel had been completed. In the meantime, the works in the south tube were also progressing with a time delay and the tunnellers were expecting to complete the excavation by the end of November. In the south tube, it has also been intended since before the start of construction to break out the relevant locations in the temporary top heading invert with a cutter wheel. According to DEGES, a total of 125 000 m³ of rock will be excavated from the two tunnel tubes on this project, although the quantity of shotcrete to be broken out is luckily much less, as confirmed by Dipl.-Ing. Björn Döppner,
site manager for the JV partner Züblin. “Through the use of the cutter wheel, we can break out the shotcrete almost cleanly sorted, in contrast to using a breaker attachment or drill and blast. This saves our client considerable disposal costs.”
