New trenchless technology for small diameters and long drives and its use in underground cable installation
With the new legislation for Grid Expansion in Germany passed at the end of 2015, the trenchless installation of underground cables presents a challenge for grid operators and engineers. To ensure the required connection from North to South until the year 2025, a total of 2,250km of new lines have to be installed underground, where a minimum of 10% are expected to be using trenchless technology. With minimum disruption of surface and environment, trenchless technology complies with residents and landowners and can considerably speed up approval procedures. Besides the proven tunnelling and pipeline methods, which are mainly used for sensitive crossings, a new technology for separate cable installation was required. The aim was to develop a highly efficient solution to compete with open-trench methods. By the help of an automated system, cables have to be installed quickly over long distances, with low investment in equipment and manpower. Herrenknecht AG has now developed a technology which meets these requirements. It installs close parallel underground cables with minimal overburden of 1.5m over long distances. The tunnelling machine AVNS type with powerpack and slurry pump in the machine has a boring diameter of 505mm and is designed for 1,000m drive length. These features also make the machine concept interesting for other trenchless technologies. With the use of the AVNS, longer drive lengths can be realized even in small diameter pipe jacking of 250mm upwards, depending on geology. Furthermore, this machine can also be used for Direct Pipe® and opens up the lower diameter range from 18” to 30” pipelines.