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Through the underground at high speed

SCHWANAU/GERMANY, April 08, 2013 - Pipe Express exceeded the expectations of its developers during its first use on the jobsite. A smooth construction process and high tunnelling speeds provided for happy faces at the end of the 500 meter long installation route, causing optimism for the future of this new construction method.

energy supply for Pipe Express

During this mission, the trenching unit for the energy supply was drawn by a trailer.

"The intense work carried out at the Schwanau test plant has now paid off", said Andreas Diedrich, project manager for the development of Pipe Express at Herrenknecht. Understandably enough, he had traveled to Holland in a state of nervous excitement. Sevenum, a municipality close to the German-Dutch border, was the right place to use Pipe Express in practice under jobsite conditions for the first time.

The testing field was a 500 meter long section of the gas pipeline from Odiliapeel to Melick with a total length of 66 kilometers. The transport pipe with a diameter of 48' is being built by Visser + Smit Hanab for the Gasunie grid operator. In talks between Herrenknecht, Visser + Smit Hanab and Gasunie, the managers responsible agreed to test Pipe Express's practical viability on this section.

The testing equipment consisted of a Pipe Thruster owned by Visser + Smit Hanab with a maximum thrust and pulling force of 500 tonnes, as well as a newly-built Pipe Express Machine, comprising a tunnel boring machine and a trenching unit which is fixed to and carried along with the tunnel boring machine. The main task of the trenching unit is to convey the soil loosened by the cutterhead from the cutterhead to the surface through a slit.

The pipe installed was a 48' steel pipe with a thin standard PE coating (3-3.5mm), which is usually used for open installation. This was not a problem, since the existing construction ground was fine sand without any stones or other deposits which could have damaged the coating. The control cabin of the machine was located beside the construction launch pit with a view towards the Pipe Thruster. The power pack for supplying the tunnel boring machine and the trenching unit with energy, as well as the equipment to supply the bentonite necessary to lubricate the pipe string from the cutterhead, were carried along on the route with trailers in line with the tunnelling progress.

Since this section of the route was originally planned for installation in the open construction method and since everything was already prepared, the section had been cleared at a width of 41 meters. Preparations for groundwater conservation had also already been made. Because of this, the real advantages of Pipe Express, i.e. a reduction in land use thanks to the clearly reduced route width and the possibility of driving through groundwater, could not fully come into their own. Thus, the main focus was on testing the practical capability. In this respect, all expectations were met. The sandy soil, which was easy to loosen, allowed advance rates of 1.2 meters per minute. "In this respect, it was not the machine technology which imposed a limiting factor, but the power pack for the Pipe Thruster's energy supply which limited the tunnelling speed", explained Andreas Diedrich. As the 500 meter long pipe string was lubricated with bentonite from the cutterhead, functioning in the same way as it does in Direct Pipe®, jacking forces of 230 tonnes were sufficient. However, in terms of installation depths, the complete machine range was tested. The machine started with a small overburden of 1.0 meter, however overburdens of 2.50 meters were achieved during tunnelling without any problems.

Pipe Thruster by Herrenknecht

Powerful: The Pipe Thruster used develops a maximum thrust force of 500 tonnes.

In general, Herrenknecht engineers are highly satisfied with the jobsite results. The experience gathered in the Netherlands is now to be used to perfect the system. This includes the construction of a self-propelled surface vehicle for supplying the boring and the trenching unit with energy. And there are considerations to place the trenching unit onto a crawler chassis to minimize the ground pressure. The developers see further optimization potentials with regard to pipe string lubrication. The pushing forces necessary might also be reduced in future. With respect to the actual performance parameters, Pipe Express® not only fulfilled the jobsite requirements established in the "project specifications" beforehand, but even exceeded some of them.

At the end, there was also praise from the construction company. "I am very enthusiastic, everything worked excellently", says Wilko Koop, managing director at Visser & Smit Hanab. He sees the future chances of Pipe Express in a positive light. Arguments in favor of this method, such as narrower installation routes, no groundwater lowering, less impact on the soil due to less machine use and reduced heavy jobsite traffic, and even lower CO2 emissions are convincing reasons for contractors when realizing new pipeline projects in view of increasingly difficult approval procedures and acceptance problems among land owners. "We are happy if we can help our clients already in the planning phase to get a project fit for approval by implementing state-of-the-art technologies" said Koop. Pipe Express is another tool now available.

Pipe Express

Pipe Express is a semi-trenchless installation method. The essential system components are a tunnel boring machine, a trenching unit and a Pipe Thruster. The tunnel boring machine is assembled at the tip of the pipe string to be installed, the loosened soil is conveyed to the surface by the trenching unit from the tunnel boring machine through a slit which has been milled into the soil. No slurry is required to remove the soil. The Herrenknecht Pipe Thruster takes care of the pipe string jacking process.
Pipe Express is ideal for installing steel pipes with diameters of 32" to 60". With regard to the drive lengths possible, Herrenknecht is now talking in terms of up to 1,000 meters with a tunneling performance of up to 1.50 meters per minute. Initially, variable overburdens of 0.50 to 2.50 meters are feasible.

Written by Artur zu Eulenburg