With the last reaming bore the prepared line(s) is/are connected to the reamer and is/are pulled-in through the bore hole. A swivel joint prevents the transfer of the rotating movement of the drill string onto the line string(s).

1. Loosening of the soil or rock
2. Cleaning of the borhole and removal of the spoil through the annular space between the drill rod and the wall of the borehole towards the ground surface
3. Support of the borehole walls to prevent collapse, reduction of the diameter as a consequence of plastic deformation and borehole collapse
4. Preventing inflow of large amounts of liquid material into the borehole from pore- and fissure …

The aim of the steerable bore is to follow the given way as accurately as possible. That requires the

• possibility of directional correction
• permanent evaluation of position and location
• determination of the optimal dimension and duration of steering

The current location, rolling, inclination and depth of the drill head are determined by means of:

• walk-over process
• wire-line process
• miscellaneous processes

Because the unmanned, non-steerable techniques have severe limitations in terms of directional accuracy, international efforts have been underway since the 1970s to develop unmanned steerable techniques for trenchless installation of cables and pipes.

The following are included in unmanned, steerable soil displacement techniques:

• Steerable impact moling
• Pilot pipe jacking with soil displacement

The steerable impact moling (steerable IM) corresponds in principle to the non-steerable impact moling .

The steerable displacement hammer possesses a stepped displacement head (steering head) situated in a housing. It can be slant adjusted and can be diverted for a desired directional correction by rotating the torsion-stiff compressed air hose by hand into the required direction [Ramei00].

In trenchless installation, a sensor (sonde) is situated in the front housing part of the displacement hammer and this is localized by means of the Walk-Over method and makes possible the determination of the position, depth, gradient and roll of the displacement hammer [Hesse94].

There are at least two working steps:

• Creation of the bore
• Pulling-in the line(s) after completion of the boring by pulling-back the compressed air hoses or the drill strings.

In the technique of unmanned, steerable pilot pipe jacking, the installation of the supply and disposal lines is always carried out in at least …

Phase 1: Pilot boring

After installation of the jacking station in the starting shaft, the pilot bore is created in the first phase . The pilot drill string consists of the pilot drill rod string and a hydraulically extending displacement and steering head .

Phase 1: Pilot boring

A steered pilot boring is established from the starting shaft to the target shaft with a commercially available pilot pipe jacking plant using the soil displacement method .

Phase 2: Pulling in the anchor pulling string

After reaching the target shaft, the pilot drill rod string is pulled back to the starting shaft and at the same time a high-tensile anchor pulling string is pulled into the pilot boring .

Phase 3: Reaming boring

In this step, a flushing head is attached to the anchor pulling string in the target shaft to act as a reamer and this is additionally equipped with an adapter for a tensile restrained coupling to the pipeline to be pulled in. When this work is complete, the anchor pulling string with the coupled pipe string is pulled back …

The development of unmanned steerable techniques with soil removal is based on the application limits of the unmanned non-steerable techniques.

Due to the application of steerable techniques unscheduled changes of direction can be adjusted as well as scheduled curves can be jacked.

The following methods belong to the unmanned, steerable soil removal techniques:

• Pilot pipe jacking
• Microtunnelling
• Horizontal directional drilling (HDD)

In the technique of unmanned, steerable pilot pipe jacking, the installation of the supply and disposal lines is always carried out in at least two but a maximum of three sequential phases.

A steered pilot boring is first made according to the principle of soil removal.

A subsequent unsteered expansion or reaming bore by means of …

Method of operation and sequence

1^st phase: steered pilot boring (bore hole diameter 419 mm) to the target shaft according to the soil removal principle with the help of a jacking …