Moling

Impact moling is a very widely used method of installing small diameter pipes, ducts and cables in the utilities industry. Utilities companies around the world use this technique  to service gas, water and sewerage mains, often under roads, pavements  and driveways, minimising the need for excavations. Advantages of impact moling are very low operational costs, simple operation and minimal disruption to the public.

The method uses displacement to create a bore and thus is the most appropriate for compressible soils. Difficulty can arise with cobbles, dense dry clays due to the difficulty in compaction and with loose sands and gravels due to collapse of the borehole. In order to ensure successful completion of an impact moling job, it is essential to know the ground conditions and to identify the depth and location of all existing utilities and other underground objects nearby.

How To Mole

  1. The bore path, surrounding area and launch/receive pits should be surveyed with suitable cable and pipe location tooling. All available survey drawings should be checked for buried utility positions.
  2. The launch/receive pits should be excavated to fit the length of the mole and the width of the cradle or operator.
  3. Measure the length of the bore from the nose of the mole and mark the air supply hose to highlight when the mole has travelled the correct distance and should have arrived in the receive pit.
  4. Position the red and white sighting staff in the receive pit on the line of the required bore, position the foot aiming frame foot against the face of the receive pit wall at the point you require the mole to arrive and put a tape marker on the sighting staff at the height of the sight of the aiming frame.
  5. Stake or brace the launch cradle into the bottom of a level launch pit, secure the mole, line up and level the launch cradle adjusting bolts until the sight cross hairs target the tape marker put on the sighting staff when the aiming frame is resting securely on the mole.
  6. Safely clear the air supply hoses of debris, adjust the lubricator to supply a fine mist of mole oil.
  7. Engage forward operation and open the air control valve on the lubricator to start the mole, reduce the airflow to a steady tick over to gain traction, gently enter the ground, with the operator periodically stopping to check the line/level with the aiming frame and adjust the launch cradle bolts to ensure an accurate bore.
  8. Once fully in the ground the air control valve is set to attain optimum power for the prevailing ground conditions.
  9. Upon reaching the receive pit, disconnect the mole and utilise the air supply hose to install the new utility.
  10. Alternatively leave the mole connected to the air supply hose, attach the new utility to the front of the mole and reverse pull from the receive pit to the launch pit.

Key Points

  • Ensure the correct diameter mole is chosen for the pipe/duct/cable to be installed. (Minimum 10% larger)
  • The minimum recommended moling depth is 10 times the mole diameter to prevent mole rising during bore.
  • Always use an in-line lubricator with the factory recommended mole oil, do not over fill the lubricator.
  • Check the forward and reverse mechanism of the tool is fully operational prior to entering the ground