Going trenchless for pipeline landfalls

Construction works can have significant environmental impacts. Herrenknecht AG breaks down the benefits of trenchless solutions in pipeline landfall installations.

When it comes to environmental impacts, trenchless solutions are indispensable to maximise protection and achieve public acceptance in coastal infrastructure projects.

48-inch Direct Pipe MTBM recovery in New Zealand. Image: McConnell Dowell Constructors Ltd

In addition to the well-known horizontal directional drilling (HDD), slurry microtunnelling methods such as pipe jacking and Direct Pipe are the most widespread techniques to construct casing tunnels or install pipelines, both with jobsite installation onshore and subsequent subsea recovery of the microtunnelling machine.

Several industries benefit from the further development of these slurry microtunnelling methods and the wide range of opportunities they provide.

Important milestones have been achieved on the coast of Mexico, where a 2246m pipe jacking sea outfall (ID 2600mm) and a 56-inch Direct Pipe have been executed for the Texas-Tuxpan pipeline.

Another application of trenchless shore approaches are seawater intakes and outlets for desalination. Due to water scarcity, desalination plants are being built all over the globe.

All-electric HK300TE HDD rig in The Netherlands. Image: Herrenknecht AG

The pipe jacking method

A launch shaft is excavated at the landside where the jacking frame is installed. Its hydraulic jacks are used to push the jacking pipes through the ground out to a predefined target point on the seabed. At the same time, a remote-controlled microtunnelling machine excavates the soil at the tunnel face.

This means no personnel have to work in the tunnel during construction. The position of the remote-controlled machine is monitored by a guidance system. With smart lubrication of the pipe string, by a volume-controlled bentonite lubrication system, and the use of interjacking stations, friction forces along the tunnel and respective jacking loads of the jacking frame in the launch shaft can be managed.

Tunnelling machines used for sea outfalls are additionally equipped with a subsea recovery module, consisting of a steel can with bulkhead to close the machine, and hydraulic cylinders to separate the machine from the pipe string. The required hydraulic lines for these cylinders are connected by divers to the outer skin of the recovery module.

Pipe jacking sea outfall principle. Image: Herrenknecht AG

In most cases the tunnelling machine has to be recovered and lifted up to the surface via a crane on a barge or on a jack-up platform. It is also possible to bring the machine to the surface by flotation through the use of air bags, fixed by divers to the lifting eyes of the machine.

One example of this method can be seen through the Sur de Texas-Tuxpan gas pipeline, which connects the coasts of Texas and Mexico across the Gulf of Mexico.

A total of three landfalls were realised for the installation of the pipeline: two with the Direct Pipe method and one with pipe jacking.

With a drive length of 2246m, the pipe jacked casing tunnel (ID2600, OD3200) in Altamira, Mexico, executed by Eurohinca, set a new benchmark in terms of sea outfall tunnel construction and long-distance pipe jacking.

Subsea recovery module with hydraulic cylinders and bulkhead for AVN1800. Image: Herrenknecht AG

The Direct Pipe method

The Direct Pipe method for trenchless installation of prefabricated steel pipelines combines slurry microtunnelling technology with the so-called Pipe Thruster, a thrust unit developed for HDD originally.

Direct Pipe incorporates the advantages of slurry microtunnelling to enable trenchless pipeline installation in difficult ground conditions, while reducing risks typically associated with HDD.

Due to its high accuracy and wide application range regarding geological conditions, Direct Pipe is a very competitive method to both HDD and open-cut installations when shore approaches of pipelines are being considered.

Especially in highly permeable or heterogeneous soils, this installation method is considered the safest and most reliable technology, as it installs the pipeline in a single step, with permanent borehole support. Like microtunnelling, the cutting head is equipped with tools consistent to the geological requirements.

This ensures high performance in the respective ground conditions and makes Direct Pipe easily adaptable to a vast variety of ground conditions.

This can be seen through a water treatment outfall in New Zealand.

Just under four months after launch for the first, 1930m long drive, the site crew in New Zealand’s Whangaparaoa could report the successful breakthrough of the DP-MTBM “Blanche”.

With the second drive, over a length of 2021m, the DP-MTBM tunneled its way through the New Zealand subsoil out to the sea, setting a new distance world record with Direct Pipe technology at the time.

The role of HDD

In the realm of trenchless pipeline landfalls, HDD is widely recognised as a proven method, offering significant economic advantages. However, in certain cases, subsurface conditions may not permit its application.

With increasing environmental awareness and a rising number of HDD projects for the installation of pipelines and underground cables and landfalls, smaller installation diameters are required.

This increases the potential for smaller rig sizes, reducing emissions and saving resources.

All-electric HDD rigs, such as HK300TE and HK45CKE, are a significant step towards the energy transition, making green energies usable in the drilling industry.

A directly electrically driven rig enables the use of green electricity and assures higher efficiency without the losses associated with the hydraulic system.

Herrenknecht´s first all-electric rig HK300TE has already completed several HDD crossings in various ground conditions up to date.

In Belgium, Germany and the Netherlands, the HK300TE all-electric trailer rig was used to install water and sewage lines, cable protective pipes and gas pipeline sections, with up to more than 1300m of single crossing length.

Expanding the all-electric rig fleet, in addition to the 300-tonne all-electric HK300TE rig, the next focus were the medium-sized rigs, such as the 45-ton range and with the new all-electric HK45CKE.

The driving force to reach into this size range, which is currently the smallest rig made by Herrenknecht, was the development of the power grid in central Europe.

For more information, visit herrenknecht.com

This article featured in the May edition of The Australian Pipeliner. 

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