HDD: crossing beneath the Main-Danube-Canal

The Main-Danube-Canal (MDC) runs over a length of 171 km in Bavaria and connects the Main and Danube rivers from Bamberg to Fürth and Nuremberg to Kelheim. With its small but beautiful harbour, the town of Fürth lies on the banks of the canal over a length of just under 13 km. In 1970 a harbour bridge was built here as a traffic connection between the two districts of Atzenhof and Unterfarnbach, also acting as a support for various supply lines for the city. Today, after more than 50 years, this harbour bridge is really in need of renovation and may even have to be demolished.

The municipal company under private law of the city of Fürth, infra fürth gmbh, as the supply and network service provider for the approximately 128,000 inhabitants of Fürth, recently decided on how to ensure an uninterrupted service supply. Whether the bridge was to be renovated or demolished was uncertain, so it was only logical to establish the new supply lines for electricity, internet and telecommunications together beneath the canal via a culvert to connect to the existing roads on both sides of the canal. In the run-up to the project, water regulations had to be fulfilled, the protection of nature and the environment had to be considered, property conditions had to be clarified, the condition of the building ground had to be examined and logistical questions and problems needed answering or solving. Of course, professional know-how, a lot of experience and the necessary technical equipment would also be required.

For the actual pipe installation, infra fürth gmbh decided to appoint Hauck Tiefbau GmbH, based in Großheirath. Providing many years of experience, extensive know-how and use of the latest techniques, the family-owned company with its 50 employees sees itself as a trenchless installation specialist – and rightly so. Furthermore, for the environmentally friendly trenchless methods in cable and service line installation, the relevant outstanding equipment in Hauck’s machinery and vehicle fleet were a major factor.

A particularly powerful and reliable HDD bore rig was needed here. The culvert was to be produced with an OD 500 SDR 11 casing pipe with protection coating, into which a whole bundle of various cable protection pipes (for cable fitting) was to be pulled in. Hauck therefore selected the midi-horizontal bore rig, GRUNDODRILL 28Nplus from TRACTO, for the pilot bore hole over approximately 200 m in an expected great depth and then carried out all necessary preparation work and arrangements to start drilling. Off they went.
 
The alternating layers of abrasive sandstones and tough, very compact clay layers were difficult to master in terms of tooling and drilling fluid. In addition, the necessary approval from the responsible waterway network and shipping authorities included the requirement to apply a wire-line-method to ensure constant control for compliance with the positional and height (depth)-related route specifications. This called for the compact rotary detection system Opti-Trac from Sharewell HDD for this purpose. By using this system, shipping on the waterway was not interfered, as there was no need to access the canal for detection reasons (as would have been necessary with the walk-over-method).

The total distance for the pilot bore from one bank to the other under the MD canal was about 200 m and the bore diameter was 170 mm. The GRUNDODRILL 28Nplus, converted for cable-guided drilling with a mud motor and with PDC-chisel, started drilling from the starting pit to the left of the harbour bridge. Due to the narrow conditions, a rather steep penetration angle (55%) had to be selected in order to achieve the necessary, specified minimum depth under the canal in good time. With a maximum depth of 26 m achieved in relation to the starting pit, the bore head worked its way forward metre by metre with an average thrust of 20 kN and an average drilling fluid requirement of 300 l/min.

Upon arrival on the opposite bank of the canal, the bore head was exchanged for a backreamer. A total of 5 expanding processes brought the final bore hole diameter to 700 mm. After a bore canal cleaning run was completed, all that needed to be done was move the bore rig from the starting pit to the target pit. The PE pipe length OD 500 SDR 11 with protection coat (12m-single pipes welded together) was filled with water und pulled in without any trouble whatsoever.

Now, only the PE protection pipes were missing, inside the OD 500 pipe length, in order to pull in the various cable and service pipes. This meant pushing the drill rods back through the completed protection pipe, then attaching the corresponding pipe bundle (4 x OD 140 for power cables, 1 x OD 90 for control cables, 5 x OD 50 for fibre-optic cables, 1 x multi-pipe system for telecommunication) and pulling it all in with precision. This just left the existing starting and target pits to be enlarged, in order to tie the new service pipes to the existing paths on both sides of the canal.

The entire construction task – jobsite set-up, pilot bore, expanding processes, installation of PE-coating pipe, installation of PE-protection pipes, insulation work, civil engineering for the re-connection – took just under two months and required a lot of good instincts as well as loads of experience and special know-how. 

„As a client we can only confirm that the interplay of sound project planning, the application of a modern installation technology and execution by qualified partners formed the basis of our success. We accepted the challenge in order to guarantee a secure service supply for Fürth in the long term. For complex projects, innovative trenchless installation is always the perfect alternative to conventional pipe installations”, according to Gerhard Pfob, infra fürth’s project manager.

Thanks to the excellent planning and professional execution with the GRUNDODRILL 28Nplus and a fantastic bore team, the supply of electricity and a fast internet for the inhabitants of Fürth was ensured for the future with just one construction project.