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“The main feature of the open front drilling technique is that the front of the pipe is open. A drill head is located at the front of the initial pipe. The open front technique is not suitable for drilling below the groundwater level, unless groundwater recession is possible by draining at the location of the pipe jack.”

Open front drilling technique (oft)

Auger method

In this technique, a pipe, possibly fitted with a cutter head or drill head, is driven under the object to be crossed. The front of the pipe is open. An auger placed in the pipe conveys the incoming soil back to the starting point. We use this method for diameters from 200 mm to 1600 mm.

a. Guided Auger Boring (GAB)

When to opt for a Guided Auger Boring?

Guided auger boring starts with a so-called “straight pilot drill” which enables precise determination of the trajectory for the delivery pipe to be installed. We apply guided auger drilling in order to install pipes with a diameter of 200 mm to 1600 mm with greater precision. When drilling the pilot rod, we use a modified theodolite and a LED probe to check the direction and height. The cutter head of the delivery pipe is then attached to the pilot rod. As it is being driven through the ground, the pipe follows the pilot rod, which is then removed in sections at the receiving side. The incoming soil is conveyed by an auger through the drill pipe to the jacking pit. And so the delivery pipe is positioned precisely along the original trajectory of the pilot rod.

What are the advantages?

  • The cutter head on the front pipe element prevents crumbling at the bore front.
    How does it work?

A pipe element is driven out of a delivery funnel into the soil, using jacks. Once a pipe element has been driven into place, the jacks are withdrawn and a new element can be attached and driven. The open front technique is not generally controllable, and deviations can therefore occur during the jacking process, as the cutter head will always take the path of least resistance. There are two methods for the open front technique, depending on the form of excavation, namely manual excavation and the auger method. In both methods, the drilling trajectory is either straight, horizontal or at an angle, either inclining or declining.

Open front drilling technique (oft)

b. Rocket plough installation (OFT-R)

When to opt for a Rocket plough?

The pneumatic installation technique is often used to drive pipes under roads, having the advantage that there is a little hinder for the surrounding area. Another advantage is that it is inexpensive versus hydraulic installation techniques. It is only suitable for use in a straight drilling trajectory. The diameter is limited, depending on the method used. Van Leeuwen Trenchless Technology offers this technique for the installation of steel pipes of diameters from 114 mm to 1220 mm (4” – 48”). Installation is possible in lengths of 25 – 80 metres. This is a non-steerable technique with limited accuracy, and there is therefore a reasonable risk of deviations.

What are the advantages?

  • Little hinder for the surrounding area (when not in a densely populated area)
  • Inexpensive versus hydraulic installation

    How does it work?

The soil rocket plough can thrust or drag the pipeline through the soil. The rocket comprises a steel cylinder in the form of a torpedo, containing a pneumatic piston. The cylinder forcefully rams an anvil at the front of the cylinder. The force of the piston against the cylinder moves the rocket forward. The piston is then pulled back again and the process is repeated. The friction between the soil and the cylinder keeps the rocket in place during the backward movement of the piston.