In the last five months of 2011 Visser & Smit Hanab undertook four 56" HDD drillings at the NEL natural gas pipe at Lubmin, to Rehden. These were: the Schaale (700 m long), Boize (650 m long), Elbe (1078 m long) and the Wesser (760 m long). 56" is an exceptionally large size for an HDD. To date only a few have been undertaken in
The drilling under the Elbe was drawn down 1078 m at 56", within nine hours; with a tensile force that never exceeded 300 tonnes. As such the drilling amounted to more than a kilometre in length; with this diameter this can easily be referred to as a groundbreaking project. Originally these intersections were included as a Microtunnel in the permit requests, but partly due to previous successes, an alternative HDD suggestion was proposed by Visser & Smit Hanab and Bonatti.
Ultimately Visser & Smit Hanab undertook all four drillings in this complex project.For each of the four drillings a separate hole was first drilled, parallel to the actual drilling. Here an 8" pipe was drawn down that during the drilling was also utilised as a mud return pipe. After completion it was used as a pipe sleeve for a fibreglass cable.
During the initial drillings some boulders of considerable size were encountered underground. Thanks to a stone catcher especially designed by Visser & Smit Hanab, these stones could be scooped out of the drill hole relatively easily, and the works resumed.
In view of the soil condition and the time specifications this was an enormous challenge. In addition, a great amount of prestige was at stake. In spite of all these factors and the external pressure, the deadline was effortlessly met.