New Nitrogen Pipeline for the University Hospital Bern

It is not hard to imagine that the infrastructure for operating such a high-technology complex is very expansive and has to be continuously adapted to the requirements. In order to extend the pipeline network a new nitrogen pipeline had to be installed from a fuel depot into a building housing the intensive care, casualty and surgery units (INO).

Liquid nitrogen, as a medical application, is used for freezing tissue and cells at temperatures as low as -196 °C, the so-called "cryopreservation". For the new pipeline a vacuum-insulated pipe with an outer diameter of 63 mm, which could  bear up against these sub-zero temperatures, was to be installed inside a protection pipe PE NW 280 S8.

In order to maintain the operation of the hospital routine without interruption the municipal office for property of the Canton Bern commissioned the company Zemp Leitung- & Tiefbau GmbH with the task of installing the new nitrogen pipeline without trenches by means of a fluid-assisted HDD bore. Company Zemp from Wiggen/Switzerland is a specialist for trenchless technologies, particularly the HDD method. For this sophisticated bore through grade 5 - 4 soils with rock inclusions up to 10 cm in diameter, the GRUNDODRILL 18ACS applied. This drill rig, particularly suitable for bores in rapidly alternating soils and even rocky formations, has served the company well on several impressing occasions.

The 70 m long bore path on the clinic premises, densely covered with buildings, took its course past the hospital chapel and into a ventilation room in the basement of the INO building. Due the very confined space in the launch area, a 2.50 m high earth dam between the building and the fuel depot was chosen as the starting place for the drill rig by the parties involved. In order to avoid damage to the existing pipelines inside the building the bore into the 3 m deep storage room had to maintain a target precision of +/- 20 cm horizontally as well as vertically. All in all, this was just the right job for the experienced drilling crew of the pipe laying experts Zemp.

The construction works started in May 2015. An excavator was lifted to the launch area with the help of a truck crane to dig out the start pit for the pilot bore and another pit for collecting the drilling mud. Then the GRUNDODRILL 18ACS, weighing the whole of approximately 15.2 tons, was placed onto the banked-up starting place by means of a 100 t truck-mounted crane.

The pilot bore, reaching a depth of up to 6.50 m, caused no problems. On arrival at the target a core hole of 450 mm in diameter was drilled through the wall of the building into the ventilation room to allow pulling the backreamer of Ø 400 mm in. One single reaming operation was sufficient to pull the new pressure pipeline through the bore path. As the basement offered very little space the single pipe segments were no longer than 2.50 m and had to be welded together in situ to form 12.50 m long pipe strings. During the process of pulling in such a previously prepared pipe string was welded on every 12.50 m.

The drilling mud was collected in a 500 l basin at the target point in the basement, from where it was pumped into a pit in the access area of the casualty department via a 60 m long line. The high share of gravel did nothing to make pumping any easier, but was not really a great drawback for the pipe pulling operation.

The final works like primary cleaning of the buildings, new installation of an inspection chamber and disassembly of the machine with the truck-mounted crane having been completed, the new line was turned over to the satisfied customer after only 10 working days. "Once more, the merits of trenchless installation in general were proved by this project, especially in connection with the TT technology. Thanks to the reliability and flexibility of our GRUNDODRILL 18ACS, this measure was happily resolved, drawing to a profitable close", was the satisfied conclusion of the company owner, Markus Zemp.

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