The versatile nature of modern microtunnelling is enabling safe, trenchless installations of pipelines and cable protection conduits on and offshore.
When conventional horizontal directional drilling (HDD) reaches its technical or environmental limits, new approaches are being taken to get the job completed.
With the global energy transition and the rapid expansion of offshore wind energy, the demand for landfall connections in Australia is expected to rise significantly.
These landfalls are essential for transmitting power from offshore wind farms to the onshore grid via export cables.
Microtunnelling methods with continuous mechanical borehole support throughout the entire installation process, offer a safe solution for installing these cables in sensitive coastal zones, especially where HDD is not applicable.
Additionally, the development of offshore gas fields requires similar landfall infrastructure, often in challenging geological conditions or protected areas.
To meet these demands, the drilling industry is beginning to adopt advanced, low-impact technologies capable of covering a wide range of pipeline materials, diameters, and installation lengths.
Ambitious goals toward climate neutrality and a zero-carbon footprint not only require the development of modern, sustainable infrastructure but also place high demands on the construction methods used.
The SubCo SMAP project in Australia is a prime example. As the world’s first zero-carbon long-haul subsea cable system, it demonstrates how environmentally responsible design must be matched by equally sustainable construction practices.
Such projects require alternatives to open-cut or HDD. Microtunnelling technologies such as pipe jacking and Herrenknecht’s Direct Pipe technology can offer a safe and sustainable solution for installing cable conduits beneath beaches and dunes, minimising disruption to marine ecosystems, preserving water quality, and ensuring compliance with strict environmental regulations.
The direct pipe method combines microtunnelling technology with a Herrenknecht Pipe Thruster to enable trenchless installation of prefabricated steel pipelines in challenging ground conditions.
Originally developed to assist HDD operations, the Pipe Thruster pushes the welded pipeline forward in 5m strokes while a slurry microtunnelling machine (AVN) simultaneously excavates the borehole.
This one-step process allows for the safe and efficient installation of certified pipelines with diameters ranging from 24–60 inches, minimising environmental impact.
Direct Pipe is a very reliable technology in highly permeable or heterogeneous soils due to its high accuracy and wide application range regarding ground conditions, maintaining permanent borehole support.
The cuttings are transported to the surface through dedicated slurry lines inside the pipeline. Thus, the borehole itself is not pressurised, preventing hydraulic formation fracturing (frac-outs) and inadvertent fluid returns.
This is pivotal to the protection of coastal environments, and constitutes an advantage over HDD’s pressurised and open borehole.
In outfall projects for shore approaches, the complete Direct Pipe jobsite equipment and the prefabricated pipeline are located on land, costly offshore operations are reduced to a minimum.
In addition, the overall underground construction hardly depends on weather or marine conditions. This makes planning and execution much more reliable, saving time and costs.
Remote-controlled recovery of the DP-MTBM from the seabed is the only part of the process needing maritime operations – however, it can easily be postponed since it is the very last step in the process and the pipeline is already in the ground.
The Direct Pipe method can be adapted to install non-pressure-resistant pipes like HDPE, often used as cable protective pipes. One approach involves inserting the HDPE pipe into the steel casing, which is then pulled back and removed leaving only the HDPE in place.
For the first time, this technique was successfully used in 2024 on the Coastal Virginia Offshore Wind (CVOW, USA) project, where three Direct Pipe systems installed nine landfall sections under tight deadlines.
This project provided an ideal opportunity to test jet pump technology under near-perfect ground conditions with a 42 inch diameter.
Direct Pipe demonstrated its highest flexibility in addressing the complex technical and environmental challenges of shore approaches in the offshore wind sector, with valuable experience gained to make this technology an indispensable complement to HDD.
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