DTH steel casing drilling for pipeline construction in hard ground and rock conditions: technology and case examples
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Jouni Jokela
Kimmo Juvani, Jouni Jokela, Tuomas Lassheikki, Manuel Rohr
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In hard ground and rock conditions, known technologies for trenchless pipeline construction suffer either from their need of drilling fluids or from inadequate drilling/jacking progress. Geonex Oy presents a DTH steel casing drilling technology which is practicable for these “though cases”. This technology uses a pneumatic hammer located directly behind the drill bit. The DTH-Hammer and drill bit combination pulls the casing pipe behind them. Behind the hammer are auger rods which work as conductor for the pressurized air. The Auger rods also convey the soil throughout the casing into the launch pit. Expansion or displacement of soil does not occur around the casing pipe. The steel casing enables a good precision of 2-3% in medium or hard soil types. Weakness of this method is in very soft soil and the lack of active steering. The maximal length of each drilling is limited to approx. 100m (~300 MPa) due to the attrition of the ring bit. DTH steel casing drilling is applied in Scandinavia for more than 20 years. Over 200 km in length and more than 10’000 holes have been drilled successfully. With several intervention points (launch pits), this method can be applied for the entire pipeline path. Due to its characteristics, it is often applied to pass under special obstacles (e.g.: river and infrastructure) in conventional trench construction or as a HDD-starting-pipe. This method in combination with HDD opens up the applicable and affordable range of trenchless pipeline construction. Three recent case examples are introduced in this presentation.

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