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Company Paasch installs cable through a nature reserve to a tide gauge
The tide gauge at Schleimünde is situated on the north side of the Schlei Estuary, approx 150 m along the coast side of the pilot island in the Baltic Sea. Energy supply and data transfer is carried out via 2 cables which run further from the gauge westwards towards a building on the south side of the pilot island. These cables no longer functioned and needed renewing. The contractor is the Water Board (WSG) in Lübeck, which obtained all the necessary permits from the environmental authorities, as the site for this task was right in the centre of a natural reserve area.

The forming force of the sea at the estuary has provided a natural beach wall landscape, which is very rarely seen. At the same time the large peninsula is also a bird sanctuary and for this reason generally not accessible for the public on the land side and can only be reached by ship. The building situated on the pilot island was built in the middle of the 19th century and is today used by the „Lighthouse Foundation“ group, which feel strongly connected with the nature conservation.

In such sensitive areas it is vital to use experienced companies, who work in an environmental friendly manner. The horizontal drilling method is seen as such a method and was intended to be applied for the installation of a cable protection pipe ND 100 over a total length of 228 m. The company Paasch from Damendorf was awarded with the task, as they were well known for being successful with similar tasks and have an excellent reputation. Paasch employs around 60 people and the company is well equipped for underground work with their 4 bore rigs.

All trenchless installation projects are different. Thanks to the Machine Ring Schleswig Holstein, Paasch has very good networks for installations between Biogas units, block heat and power plants and the end consumers. Martin Paasch: „Apart from those we have also installed more than 80 km of broadband cables and underground cables in this year."

The requirements in nature conservation areas is extremely severe. We managed to adhere to them as far as possible. Otherwise people in Northern Germany tend to say: „What must be, must be“. The approximately 3 km long path to the site was tight and basically a dirt road. To enable the access for the supply truck, excavator support mats had to be laid out over the swampy areas. The path could only be used once for the set up and then the clearance of the jobsite. Commuting traffic was only possible by sea.

The fresh water supply for the drilling fluid proved to be a problem, as the seawater, which was available in endless amounts, is not suitable for the drilling fluid, which is a mixture of water and Bentonil, a natural non-hazardous product. The only water well on the island only feed 3 m³/h – much less than required. Due to this a 20 m³ accumulator was set up at short notice. The disposal of the consumed drilling fluid was kept down to a minimum and removed with a tractor and vacuum truck.

The GRUNDODRILL Bore rig 15 N which had only been in action for a few weeks was brought into the position close to the distribution station. The pilot bore crossed beneath the beach wall, the beach and then the Baltic Sea 4,50 below the water gateway at a water level of 3,50 m. Between the tide gauge and an excavator on the mainland a cable was applied to work as a guidance, so that the measuring team could pull themselves along in their own company rubber dinghy, in order to keep a protocol of the bore head position. The timing of the bore was not chosen by co-incidence. Martin Paasch had been waiting for seaward wind and therefore calmer waves.

The pilot bore was carried out from 9.00 hrs to 13.00 hrs. The target was hit dead centre. The bore head which exited on the sea ground remained in that position until the next day. A hired work boat from Kiel with a crawler excavator arrived the next morning at 8.30 hrs from the docks at Maasholm. It took up it's position at the tide gauge and was stabilised in the sea ground with both 23 m long anchors. The experienced team of divers on board immediately started to work by fastening a cable and a position buoy to the bore head, which was then heaved upwards at backboard with the excavator to see daylight once again. The bore head was then quickly separated on board, thanks to the lock pins and break-away device, from the drill rods and replaced by a 230 mm backreamer.

The bore team from Paasch had hired a further ship beforehand, in order to transport the pipe sections, situated on the peninsula, over the Baltic Sea to the work ship. Due to the strong wind and current, it was not possible to use the company’s own rubber dinghy. The small ship from Maasholm was called into action and was a great assist in this situation. An excavator was standing on the beach at the ready and conveyed the pipe length. The bundle of 3 x 100 m pipe lengths, welded together, was pulled out to sea, taken on board the work ship and then connected to the backreamer. They were able to start the pipe pulling in process at midday. One diver checked the underwater pulling in process at the beginning, which was completed after 5 hours.

The strong wind on this dark December day caused it to feel colder and the waiting periods had to be bridged with humorous anecdotes. Lars Mohr, who has been employed by Paasch for 17 years kept the crew in suspense with stories, such as this one: „When producing a seawater extraction pipe for a public swimming pool on the island of Sylt the pipe length slipped out of their hands, just shortly before being connected and disappeared into the sea immediately due to the extremely strong current. They started searching for it in a fast boat straight away. Thank goodness it was traced just before it had reached Denmark and was re-captured.”

Back to the jobsite: The next day the water was removed from the cable protection pipe with a scraper and at the same time the pulling cable was blown through. On board the works hip both cable drums and cable racks were standing ready. The pulling in process itself took less than an hour. One diver threaded the cable into a u-iron, leading up along the gauge holm. Then the cable ends were sealed off at both side, at sea and on land.

After three working days the jobsite was cleared and the last traces were cleaned up. Now peace and quiet has returned to this nature conservation area.

Paul-Schmidt-Straße 2
57368 Lennestadt

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