With simultaneous casing drilling DTH found its way to construction industry, which had a need to find a method to get the casings into complex ground conditions. DTH drilling suits especially well for drilling foundation piles in ground conditions with hard material likes stones, boulders and different types of bed rock. Due to high productivity DTH is also gaining popularity in off shore foundation building.
There are several different types of piles that can be drilled with DTH overburden drilling system:
- End bearing piles with left in casing
- Friction piles with retrieved casings
- Vertical and battered piles
- From small diameter micro piles up to 1,5 meter casings!
Challenging ground conditions with boulders and hard rock layers have been a problem area to build temporary retaining walls and permanent wall structures. New DTH drilling techniques and tools offer an easy and fast solution to build water tight load bearing walls into complex ground layers. O-Pile walls bring huge savings in construction time with the possibility to completely eliminate temporary retaining walls.
O-Pile walls can be used as permanent structures that require high vertical and /or horizontal loads. O-Pile Walls can be used also as temporary structures in ground conditions where other solutions would be time consuming, difficult or impossible. O-Pile Walls offer high bending stiffness and, in case they can be drilled to bed rock, they can act as horizontally loaded wall that bears high vertical loads at the same time.
Horizontal DTH casing advance drilling is most commonly used for underpasses of roads and railways. Drilling is typically called as “break through” drilling. Casings are drilled from starting pit to receiving pit. When casing is advanced to receiving bit, the reaming ring bit is removed and drill string with hammer and pilot bit are pulled back to starting pit.
With DTH hammer it is possible to drill horizontally in complex ground types. It is typical that overburden conditions vary from clay and sand to material with boulders, till and solid bedrock. Sizes vary from 168 mm casing up to 1,5 meters. Hammers that are used are typically undersized to keep the drilling front as light as possible for better accuracy.
Today’s demand to improve infrastructures requires increasing number of new tunnels to be constructed also in ground conditions , which are not perfectly suitable to such purpose. The excavation of tunnels in loose soils, through fault zones, and in unstable formations require preventive actions in ground consolidation – especially for the arch but sometimes also the excavation to face of the tunnel.
Injection casings are drilled to the crown (arch) of the tunnel in order to enable safe tunnel excavation underneath the protective roof. Overlapping casings make it possible to advance drilling even in long tunnels. Tunnel portals can also use heavy load carrying pipe roofs where casings are drilled into solid rock through the loose overburden or landslide material.
