Innovative direct "pipe method' - case histories

The Direct Pipe® -method combines the advantages of the established trenchless methods Microtunnelling and Horizontal Directional Drilling (HDD). With Direct Pipe® one single, continuous working operation is sufficient for the trenchless laying of a pre-fabricated pipeline and the simultaneous excavation of the necessary bore hole. The force required to feed the pipeline forward is exerted by a new type of auxiliary device known as the Herrenknecht Pipe Thruster, which is fixed horizontally and vertically. The Pipe Thruster embraces the pipeline with its clamping device and pushes the pipeline forward. Since the pipeline is coupled to a remote controlled Direct Pipe® -machine, the transport of the excavated material is carried out by a conventional slurry circuit back through the laid pipeline.

October 2007 saw the successful world premiere for the Herrenknecht Direct Pipe® -technology installing a 464 m (1,522 ft) long steel pipe underneath the Rhine River near Worms in Germany. The pipe was planned to serve as a conduit for a water pipeline and several ducts for power and telecommunication cables. Here, the Herrenknecht Pipe Thruster provided an average thrust force of 80 tons (175,000 lbs) to smoothly push the pipeline forward. The jobsite team realized maximum advance rates of 90 m (295 ft) in 24 hours. Breakthrough was achieved only 13 days after the beginning of the construction work.

For the second time, the Direct Pipe® -method was deployed in July 2009 near the city of Emden in Northern Germany. Here, subterranean storage caverns for natural gas are being built on the Ems River. This requires flushing out salt mines to produce large underground cavities. In order to discharge the concentrated saltwater (brine), a 42-kilometer (26 Miles) long pipeline must be laid to the Outer Ems – the last 283 meters (928ft) of the outflow pipe at the “Rysumer Nacken” artificial dune field were built as Sea Outfall using the Direct Pipe® - method. Compared with conventional methods, Direct Pipe® does not require the costly and time consuming installation of steel sheet piles alongside the offshore route. With top performances of up to 9m (29ft) / hour, Direct Pipe® met the high expectations of all parties involved as far as both efficiency and environmental protection were concerned.

After the first two successful Direct Pipe® -projects in Germany the first gas pipeline crossings (with a diameter of 48”) were realised in spring 2010 with the Direct Pipe® -method in the Netherlands. The two crossings in sensitive areas, on which open trench was not possible, were part of the North-South-Trail of the Dutch gas supplier GASUNIE.

The geology on both crossings with a length of 371m and 435m was consisting of gravel, sand and also wood & stones. Maximum advance rates of 111 meters in a double shift (of 24 h) and 72 m in a single shift could be achieved. On both projects approximately 30% of the available 500 tons of the Pipe Thruster were utilized at the end. Maximum ground water depths of 5 - 10 m had to be dealt with.

Herrenknecht AG was nominated with Direct Pipe® for the internationally prestigious Hermes Award during the Hannover Fair 2008 and accepted the ISTT Product Award at the 2008 International No Dig Show in Moscow as well as the IPLOCA New Technologies Award in 2009.