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Powerful horizontal directional drilling technology for trenchless pipeline installation

Herrenknecht HDD Rigs can be employed in any terrain.

________________ With horizontal directional drilling technology from Herrenknecht, pipelines can be installed rapidly, economically and with little to no impact on the environment underneath rivers and other obstructions. HDD Rigs are highly adaptable and used mainly in stable, loose soils and rock.

Illustration of a typical HK250T Rig with a maximum pull force of 250 t and a mobile chassis

Simple but functional

Pilot drill, reaming and pipeline installation are the three basic steps in HDD.

With HDD (Horizontal Directional Drilling) pipelines are installed in three steps. First of all, the HDD Rig performs a pilot bore from the launch point toward the reception point. The rotating drill rods are precisely guided along the desired alignment by a surveying system located directly behind the drill bit. During drilling, mud pumps supply a bentonite suspension directly to the jets in the drill bit. In soft geologies, the soil is excavated hydraulically using high pressure, while in rock, excavation is done mechanically with the help of a mud motor. The bentonite mixes with the excavated material and flows back to the starting point through the annular gap between the drill rods and the borehole wall. A separation plant separates the liquid from the solid components and supplies the recycled suspension back to the bentonite circuit. The pilot bore is followed in a second step by reaming. After exiting at the reception point, the pilot drill bit, including the surveying system, is removed from the drill rods and replaced by a reamer. Using excavation tools and bentonite jets, the soil is excavated both hydraulically and mechanically while pulling back the drill rods through the pilot borehole. The water-bentonite mixture in the borehole supports the expanded borehole, removes the soil, and at the same time cools all the components. Reaming is usually performed in several passes until the final borehole diameter is achieved – which is about ­­30-50% larger than the actual pipeline diameter. In a third step, the pipeline is installed by connecting the prefabricated pipeline to the drill rods. Lifting the front end of the pipeline creates a so-called overbend and the entry angle of the pipeline is adjusted to match the entry angle of the borehole – also maintaining the minimum bending radius. Then, the pipeline attached behind the reamer and a swivel joint, is pulled back to the entry point by the HDD Rig until it reaches its final position. During this process, bentonite minimizes the friction between the pipeline skin and the surrounding soil.

Additional power for long crossings

The traditional HDD method may reach its performance limits when dealing with extremely long crossings, large pipeline diameters, or difficult ground conditions. Therefore, Herrenknecht has developed the Pipe Thruster for such demanding projects. It provides an extra thrust force of up to 750 tonnes at the exit point when installing pipelines. Due to the simultaneous pull by the HDD Rig and thrust by the Pipe Thruster, high installation forces can be applied gently and safely.

A drill bit excavates the soil in a pilot hole; subsequently, a reamer widens the borehole

Borehole support
Hydraulic support using bentonite suspension

Hydraulic conveyance of the excavated material through the annular gap using a bentonite suspension

The carriage thrusts the rotating drill rods forward and pulls them back during reaming

Tunnel lining

+ Economic and environmentally-friendly method for installing pipelines
+ Broad geological range of application: stable loose soils and rock
+ Four basic rig types for different ranges of implementation available
+ Using the Pipe Thruster, the available thrust and pull force can be increased (up to 750 t additionally)

The right rig for the job

HDD Rigs developed by Herrenknecht can be delivered in four different standard configurations. All models have pull forces between 60 and 600 tonnes (600 and 6,000 kN), a control cabin, as well as their own power supply pack powered by a diesel engine in a sound-insulated container. The output of these power packs ranges, depending on the application, from 330 to more than 1,440 kilowatts and is engineered to the customer’s requirements.

Frame Rig: Their low weight and easy transport make Frame Rigs a reliable and economical solution. Without its own transport or motion system, the Frame Rig reaches the jobsite on a regular truck trailer. A standard crane is sufficient for loading and unloading and for aligning the rig on the jobsite.

Trailer Rig: The great advantage of Trailer Rigs is their extreme flexibility. Due to their low-weight design, they can be transported with standard semi-trailer trucks. A crane is not required, neither for setup and demobilization, nor for alignment and commissioning. This makes Trailer Rigs particularly suitable for projects in which long distances in between several crossings are to be covered.

Crawler Rig: On jobsites in rough “off-road” terrain not accessible to trucks or cranes, Crawler Rigs offer considerable advantages. Their robust and mobile crawler with its caterpillar tracks enables mobility and maneuverability on difficult terrain.

Modular Rig: To be able to use HDD Rigs in remote regions, Herrenknecht has developed another innovative solution. Modular Rigs can be dismantled into two or three modules and transported in standard freight containers. On site they are re-assembled. An optional, remote-controlled crawler adds further mobility on the jobsite.

Special solutions for special projects

Corrosion-proof 150-tonne Crawler Rig in action on the French Mediterranean coastline.

Target-oriented implementation of customer-specific requirements is part of Herrenknecht’s daily business. References from successfully completed projects are HDD Rigs operating in ambient temperatures of down to -20° Celsius, a specially designed rig for a project on an Australian island where the focus on nature and wildlife preservation was of utmost importance, or corrosion-proof equipment for sea outfall projects directly along the coastline. Other specialized rigs can even be dismantled in such a way, that they can be transported by helicopter. Pipelines are successfully installed worldwide using powerful HDD Rigs from Herrenknecht. The geological application range of the proven trenchless HDD method covers everything from soft loose soils to hard rock. Ancillary HDD equipment such as high pressure mud pumps, bentonite mixing equipment, separation plants, drill rod storage, mobile break-out units, or bentonite pumps are part of the Herrenknecht portfolio.

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