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How do you install a large diameter pipe without damaging sensitive ecological environments or disrupting highly urbanized communities? Over the last two decades, contractors have increasingly turned to a method called horizontal directional drilling (HDD). HDD is a steerable trenchless technique of installing everything from pipe to cable with minimal construction footprint and minor impact on surrounding areas.
When considering the installation of large diameter pipes, which can exceed a meter (39 inches) in diameter, a trenchless installation method can potentially solve a host of problems. Here we will discuss the benefits and uses of HDD installation for large diameter pipes and review a recent case study that demonstrates this method in action.
What are the benefits of using HDD for the installation of large diameter pipes?
While trenching and excavating methods are more straightforward, they can be impractical in modern use cases due to the environment (e.g., river crossing), landscape (e.g., ecological considerations), or socioeconomic impact (e.g., roads and homes).
Enter HDD, which enables very precise borings with shallow arcs capable of bypassing subterranean obstacles like other pipes or riverbeds. This steerable boring method begins with the creation of a pilot hole that is drilled and steered along a prescribed pathway. Once the bore head reaches the end of the path and breaks the surface, the final drill-path is complete. Now, a back reamer is attached to the boring rods and the back reamer is then drawn back through the bore path. As the back reamer advances it simultaneously increases the diameter of the drill-path while also pulling the pipe into place (1).
The choice of pipe material and standard dimensional ratio (SDR) will depend on three requirements: the pressure, the service loads, and the pullback load.
Choosing the large diameter pipe material for the HDD method
Pipe can be made of materials like polyethylene, polypropylene, ductile iron, steel and PVC—essentially anything that is capable of being pulled through the drill-path. However, the very nature of HDD encourages the use of materials that can withstand the various loads and other variables present during the pullback cycle.
Pipes made of polyethylene (PE) complement the HDD method extremely well thanks to its high strength, flexibility, superior joint integrity, low weight, and long-term service life, which represents improved cost-effectiveness over many competing materials. Additionally, PE pipes have high corrosion resistance and are chemically stable—capable of transporting a host of compounds without degradation (2). PE pipes can also be manufactured to match your project needs, including very thick, solid wall HDPE Pipe.
HDD installed large diameter pipe under the Spree River, Germany
Although large diameter pipes at the highest ends of the scale had never been installed using HDD, pipes like the AGRULINE PE 100-RC meet all the technical load requirements and are tested and approved by PAS 1075 for trenchless laying techniques.
In 2016, a combination of floods, delicate environmental considerations, and high cost of repair via traditional methods compelled the use of HDD to bypass a multi-pipe rupture in the Nochten Water Pipeline near the Spree River, Germany. These groundwater and mine water pipes are essential to the nearby mining operation supplying the brown coal necessary to power the Schwarze Pumpe power station.
A new installation using the HDD method with pipes made from PE 100-RC was the most economic and easiest solution to implement (3). These pipes are permanently resistant to corrosion otherwise caused by the transported mine water. Additionally, given their high flexibility, wash borings with small installation radii are also possible. Finally, the pipes allow for significant deformation that can result from ground subsidence without danger of cracks or breaks.
The final installation required two conduits, approximately 220 m (721.8 ft.) long, to be prefabricated at OD 1200 mm (47.2 inch) and OD 1400 mm (55.1 inch) with a wall thickness of SDR 17. Segments measuring 13 m (42.7 ft.) in length would be welded together on-site. With a combined weight of 76 tons each, special roller blocks were used to reduce the force required to pull them in.
While the HDD construction technology has been widely utilized in various industries for many years, this engineering project was a world-first, providing a real-world case of a large diameter PE pipe installation using the HDD method. Jorn Stoelinga, Horizontal Directional Drilling Consultant at Visser & Smit said, “We are proud to be the first to have successfully laid such large diameter PE 100 pipes using the wash boring process. They were easy to weld, and very easy to pull in thanks to their flexibility.”
- Http://www.nodig.com, Northeast Consulting Inc. -. “SECOND EDITION HANDBOOK OF PE PIPE.” Second Edition Handbook of PE Pipe | HDPE Handbook. Accessed July 10, 2017. http://plasticpipe.org/publications/pe-handbook.html.
- “Large-Diameter Plastic Pipe Mains Are Helping Gas Distribution.” Pipeline & Gas Journal. Accessed July 10, 2017. https://pgjonline.com/2009/12/11/large-diameter-plastic-pipe-mains-are-helping-gas-distribution/.
- “Record breaking Horizontal Directional Drilling – AGRU.” Accessed July 10, 2017. http://www.agru.at/en/solutions/agruline/record-breaking-horizontal-directional-drilling/.