With a population of 25,000, of which 80 per cent live in the town area, Kiruna is well-known for its ore mines, which have been operated with great success since the turn of the last century, contributing decisively to the wealth of Sweden. Each year 2.5 billion tonnes of iron ore are transported to the docks of Narvik, 400 km away and free of ice.

The task at hand

The pipe cracking jobsite was situated directly in Kiruna, and the renewal was required because of ever-increasing leakages in a grey cast iron pressure water pipe. The local council, SE – 981 85 Kiruna, contracted Stockholm-based Oden Anläggningsentreprenad AB, SE – 80429 Gävle, for the trenchless renewal of the pipe, ND 500.

The pipe consists of 6 m length single pipes, which are coated with a 10 mm strong cement layer. The depth of the installation lengths of 120 and 125 m was between 4 and 5 m. The new pipe is a HDPE pipe, PE 100, SDR 17, OD 500 x 29.7 mm.

The equipment

Due to the material, the length and the diameter of the old pipe, the contractor decided to apply the Grundoburst 1250 CP.

The special characteristics of the Grundoburst 1250 CP are the two thrust rigs, making a continuous bursting process possible. As there is no return stroke the new pipe is pulled in at an even speed. The bursting rods with their 1.7 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 rod together.

The total length of the Grundoburst 1250 CP with extension frame is 7 m. 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 also where the new pipes with 10 or 25 m single lengths arrive from the twin installation pits. The larger length is due to a bend and a strong intrados of the old pipe in this pipe section.

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

The bore process

The Grundoburst 1250 CP was set-up, installed, ready for use within two hours.

The pushing-in process of 125 m rods for the first length required a total of one hour. Inside the machine pit, with a 12 m length the drill rod boxes could be set up in the generous space, 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 between 700 and 750 kN, with an increase to about 900 kN in the area of the sockets, therefore every 6 m.

One example of the simple handling, despite the larger dimensions, was the connection of the tools (roller blade, expander and PE pulling head) as well as the drill rods and the machine technology.

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

Result

Once more the burst rig from Tracto-Technik proved its performance capabilities. The company Oden used the Grundoburst 1250 CP for this particular application, which allows for a continuous pulling-in process, without any interruptions for the new pipes.

Due to the application of the special roller blade technology in connection with the continuous pulling force application via the Grundoburst 1250 CP, 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 performance ability of the Grundoburst 1250 CP was fully taken advantage of during the bursting and pulling-in process.