Pipe-cracking in the Arctic Circle

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KIRUNA, Sweden -- A pipe-cracking task north of the Arctic Circle may be difficult to visualize, but it happened in Sweden's most northern commune Kiruna, which covers an area of 20,000 square kilometers and is roughly half the size of Switzerland. With a total population of 25,000 here, 80% live in the town area.

Kiruna is well-known for its ore mines, which have operated with great success here since the turn of the last century, contributing decisively to the wealth of Sweden. Each year 2.5 billion tons of iron ore are won and transported to the docks of Narvik, 400 km away and free of ice.

The challenge
The pipe-cracking jobsite was situated directly in Kiruna. The Kiruna council engaged the contractor Oden Anläggningsentreprenad AB with the trenchless renewal of the grey cast iron pressure water pipe.

The pipe consisted of 6-meter-long single pipes coated with a 10 mm strong cement layer. The depth of the installation lengths of 120 and 125 m was between 4 and 5 meters. The new pipe was an HDPE pipe, OD 500 x 29.7 mm. Ever increasing leakages drove the renewal project.

The equipment
Due to the material, the length, and the diameter of the old pipe, the contractor decided to apply the GRUNDOBURST 1250 CP in consultation with the TT-country representative Vretmaskin, Stockholm. The special characteristics of the GRUNDOBURST 1250 CP are the 2 thrust rigs, making a continuous bursting process possible. As there is no return stroke, the new pipe can be pulled in at an even speed. The bursting rods with their 1.70 m lengths are placed into the burst rig with a crane without interrupting the pushing-in process. The Quicklock connection does not cause any auxiliary times, which would normally be necessary for screwing single rods together.

The total length of the GRUNDOBURST 1250 CP with extension frame is 7 meters. The extension frame is used to retain the bursting tool and the expander, together with the welded-on pipe lengths, when pulling into the machine pit.

The set-up conditions available allowed for a generously dimensioned machine pit to be set up without any obstructions. This was also where the new pipes with 10 or 25 m single lengths arrived from the twin installation pits. The larger length was the result of a bend and a strong intrados of the old pipe in this pipe section.

The burst tool to be applied consisted of a basic carrier fitted with a 500 mm cutting strip set. The grey cast iron pipe in the ground was cut open with a roller blade on the underside and pressed into the surrounding soil with the expander. The machine equipment is capable of a maximum pulling force of 1270 kN.

The bore process
The GRUNDOBURST 1250 CP was set-up, installed, and ready for use within 2 hours.

The pushing-in process of 125 m rods for the first length required a total of 1 hour. With a 12 m length, the drill rod boxes could be set up inside the machine pit, making it much easier to handle the burst rods.

The GRUNDOBURST 1250 CP was sufficiently dimensioned for the bursting and pulling in process. The pulling forces were situated between 700 and 750 kN, with an increase to about 900 kN in the area of the sockets, therefore every 6 meters.

Despite the larger dimensions, the connection of the tools (roller blade, expander and PE pulling head) as well as the drill rods and the machine technology, allowed for simple handling.

For the pulling in process of the second length, the burst rig and the extension frame were placed in a different positions. The pulling-in process itself -- after completing the preparation work -- required approximately 70 minutes per length.

The burst rig from Tracto-Technik proved its performance capabilities. Oden chose the GRUNDOBURST 1250 CP for this particular application because of its continuous pulling-in process.

Due to the application of the special roller blade technology in connection with the continuous pulling force application via the GRUNDOBURST 1250CP, it was possible in this case to keep the required pulling forces down to a minimum.

As it was a major intention to ensure a quick and trouble-free sequence of the auxiliary work, the performability of the GRUNDOBURST 1250 CP was fully taken advantage of during the bursting and pulling in process.

For more information, see: www.tracto-technik.de


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