NEL Pipeline, Crossing Paths with the Dynamic Ramming Method

Günter Naujoks, on behalf of TRACTO-TECHNIK GmbH & Co. KG
Special Collaboration

The NEL, North European Natural Gas Pipeline from WinGas in Kassel (Germany) distributes the natural gas arriving from Russia to Germany and the rest of Northwest Europe. The natural gas storage unit in Rheden is the final arrival point for the gas pipeline, which leads all the way from Lubmin. Stretching over the 440 km path from the North of Germany countless roads, rivers and railway tracks have to be crossed under.

The contract for two construction packages with a length of over 120 km was received by the company Bonatti S.p.A. from Parma in Italy. Within this framework the highly recommended company Dalcai Horizontale Wegboringen BV, a specialised company for horizontal bore techniques, based in Nijverdal in Holland, carried out three road crossings with the dynamic ramming method.

Dalcai has been specialised in the dynamic ramming field for pipeline constructions since 1999. In the last two years alone, Dalcai has carried out more than 11 km in pipelines by ramming steel pipes with the Apollo compressed air operated steel pipe rammer manufactured by TRACTO-TECHNIK GmbH & Co. KG, and has gained extensive experience, the relevant know-how, as well as the necessary routine to complete these types of bore tasks. Dalcai’s managing director, Jan-Willem Dalvoorde added these comments: "The success of the task depends on the machine technology. The rammers must be able to withstand enormous strains, if you consider, that the strongest rammer worldwide, the Apollo can produce a single stroke energy of up to 40,500 Nm.”

The three road crossings were situated close to the A24 motorway in Mecklenburg Vorpommern approx. 8  km east of Hamburg: In Perdöhl with a 34 m length, in Albertinenhof, with a 40 m length, as well in Schwartow with a length of 44 m.

A decision was made to apply the dynamic ramming method, because you can work quicker and less expensive than with a press-bore method, combined with a spiral conveyor. The ramming process does not require any pressing resistance and heavy pressing frames, has a stable direction and is also applicable with lower cover space. The pipe length, which is welded together beforehand, can be pushed forward with a propulsion speed of up to 10 m/h, so that road crossings can be completed within one working day. With the press-bore method, where only single pipe sections can be pressed forward, up to 5 to 7 working days would have to be calculated for the same task.

Contrary to the open trench steel pipes, which are surrounded by PE (Ø 1420 x 22,7 mm), steel pipes sheathed with glass-fibre is applied for the road crossings. Three pipe lengths, each with a length of 18 m were welded together, an initial pressure test was carried out and then placed on the prepared base on site.

Dalcai applied the rammer type Apollo with a striking energy of 40,500 Nm. The compressed air was supplied by two compressors with 63 m³ and 45 m³ air flow rates.

Cotter segments are generally applied for these tasks, which prevent the pipe from flaring during the propulsion process, so that the pipes can be welded perfectly together face to face. Furthermore, the form of the cotter segments allow the strike energy to be transferred evenly into the pipe length. The four-part segments can be installed and fixed in place quickly. At the same time two HDPE pipes ND 125 are fixed into an appliance on the steel pipe. The pipes are pushed in with the steel pipe and used as an empty pipe and also for the control cable.

Then the Apollo was placed in position and the compressed air supply was set up. This was followed by the successive installation of the pipe length. The cutting shoe on the first pipe strengthens and protects the pipe wall during the propulsion and minimises any casing friction occurring on the pipe surface. In compact sandy soils the casing friction is very strong for certain periods.

This did not prevent a smooth pipe installation. The pipe length arrived on the other side of the road, surrounded by an row of oak trees after only 2.5 hours. The installation process was now complete.

Then the dismantling and transportation of the rammer and compressors to the next jobsite had to be sorted out and the high pressure rinsing vehicle with 20 m³ volume was used in order to remove the soil remaining in the pipe. A rinsing head bored through the soil in two steps, rinsing the sandy soil out of the pipe in reverse mode.

With the additional pressure test of the installed pipe length, which followed, the bore measure was completed.

The ramming work was carried out in the following working steps:

• Welding the pipes together to produce one pipe length and undergo a first pressure test
• Starting to operate the water container in a 4 metre deep trench situated in groundwater
• Installing the steel pipe, coated with glass-fibre inside the prepared trench
• Preparing the pipe length by attaching the cutting shoe at the front of the pipe.
• Attaching retainer device for the carriage of two HDPE empty pipes, ND 125 (Retaining control lines)
• Application of the 4 cotter segments for the even force induction and to prevent the pipe from flaring
• Positioning the rammer with a base and connection of the compressed air via two compressed air hoses
• Rinsing out the soil in 4 hours with 120 m³ water, pumped out of a nearby river and transported to the site on a trailer.

After the complete pumping process and disposal of the rinsed out soil a final pressure test of the installed pipe length was carried out, which was then welded to the steel pipes in the open trench.

All three installations were carried out in 3 successive working days, as the working sequence was co-ordinated in an exemplary manner and despite the multi-lingual team-work (Italian, German and Dutch) carried out in a routine manner.

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