Guidance Systems

Walkover Guidance Systems

Walk-over guidance systems are regularly used during the construction process of a pilot bore. With this method the drill head is tracked by monitoring the electromagnetic signal that is being transmitted by the sonde that is inside the casing/sonde housing of the drill head. The receiver determines and illustrates on a LCD screen;

  • the drill head location
  • the calculated depth
  • the inclination of the head
  • the tool face angle
  • the temperature down hole
  • forward and backward readings (front & rear locations) to determine the direction of the bore

Wire-Cable Techniques

With this technique the bore head position data is transmitted by cable positioned inside the drill rods to the operating panel. Examples of when this technique is required are :

  1. Where high precision is required at shallow depths (between 4 and 10 metres)
  2. Under areas of interference
  3. Areas that are completely inaccessible
  4. Saltwater areas and river crossings

During the pilot bore every pipe length added must be connected to an inner rod cable that has to be clamped on to the preceding piece of cable and requires protective insulation. This system uses very precise detection systems in the bore head that measure the inclination, the directional angles (angles between the geographic north and the borehole axis = azimuth) and the roll of the bore head. Since the azimuth is often measured via magnetometers the detection system must be placed in a housing or rod made of anti-magnetic steel. The inclination and roll can be measured gravitationally, inductively or by accelerometers. Artificial magnetic fields for Horizontal Directional Drilling (HDD) bores above the surface or at the bottom of rivers are often laid out using cable loop.