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Impact moling is a method for underground pipe installation and boring which has been established in civil engineering for the last three decades.
A mole or soil displacement hammer, driven by pneumatics, creates a cavity underground, ready for pulling in short or long pipes made of plastic (PE, PVC or PE-X) and metal (e.g. St), preferably without socket ends, up to DN 200, but also any type of cable installation in bore lengths up to 40 m (depending on the soil quality), either simultaneously or in a second working step. This allows trenchless pipe laying or cable installation underneath roads and existing untility's equipment..
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For successful impact moling the required conditions are : the ground to be bored must be sufficiently displaceable. A pit is required for the start. As a rule, the mole is lying on top of an adjustable bore rig. With the aid of telescopic sight, aim is taken and the height and sides of the machine are adjusted. The propulsion of the soil displacement hammer / impact mole is performed by a piston driven with compressed air (for example one of our GRUNDOAIR compressors). External friction is required for the propulsion. If this is missing, in loose, soft soils, for example, external static support for the impact mole can be added.
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Two different impact moling methods are possible:
- Either the piston applies impact to the casing and drives
the complete displacement hammer and the attached pipe string forward with one blow (rigid system) or
- The piston first strikes the mobile multi-cutter cone
and then the casing, which means that the soil displacements hammer moves forward in two steps.
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The mole can achieve a speed of up to 15 m/h, depending on the soil characteristics. The soil cover should be at least ten times as thick as the diameter of the casing to avoid arching of the surface. TT UK impact moling machines are equipped with a reversing gear. The Grundomat impact moleing system with its mobile multi-cutter cone is simply reversed with a lever. A plug-on head with integrated transmitter or a built-in transmitter in the hose makes location of the mole possible, but is not intended for steering (for steerable moles look at our GRUNDOSTEER system) The soil displacement /moling method is described in the German guideline ATV-A 125 and in the GW 304 Pipe Laying as well as in other German standards.
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