Grundomat Impact Moles

An Impact Mole (otherwise referred to as a soil displacement hammer or an earth piercing tool) is the simplest way of getting a pipe or cable through displaceable soils such as sand, loam and gravel.

We hire Grundomat moles from 45mm to 180mm, laying product up to 125mm over bore lengths of up to 20m. Of the trenchless methods we supply, moling is the cheapest to run and the quickest to set up, which is why it is the usual answer for a new service crossing under a road or a drive.

What Impact Moles Are Used For

Impact moles install small diameter pipe, duct and cable where digging a trench would cost more than the pipework itself. Typical jobs include:

• Water mains and service connections
• Gas and sewer connections
• Crossings under roads, driveways, pavements and railways
• Electric, phone and fibre optic cable
• Ducting for telecoms and power cable
• Service runs under lawns, drives and landscaping

Used for cable rather than pipe, an impact mole is often called a cable mole, and the work is known as cable moling. It is the same tool either way: size it to the duct or the cable you are pulling in.

How an Impact Mole Works

An impact mole is a cylindrical air hammer. It works between two small pits, one to launch from and one to receive, leaving the ground in between untouched. A piston inside the casing hammers the tool forward, driven by a compressor on the surface. Nobody digs out the ground along the route. The soil is displaced sideways and compacted around the bore.

The Grundomat's stepped cone chisel head strikes ahead of the body and breaks fracturable rock, so the tool passes through stones that would push a single-piece tool off line. If the operator hits an obstruction the mole cannot break, a quarter turn of the air hose puts it into reverse and they walk it back out of the bore.

The crew can pull your pipe, duct or cable in behind the mole on the same pass using a towing head, or feed it through once the bore is open.

Ground Conditions for Impact Moling

Impact moling needs ground that will displace. Sand, loam and gravel all suit it, including ground with fracturable stone in it, which the chisel head breaks up as it goes.

A Grundomat will not bore solid rock, and it is not designed to work against rock it cannot fracture. Very soft ground is the other limit: the tool's own weight can pull it off line, so accuracy suffers in waterlogged or peaty ground. In loose sand and gravel, pull the pipe in behind the mole rather than feeding it through afterwards, because the bore may not stay open on its own.

Made ground, old foundations and buried obstructions are the common cause of a bore going wrong on urban sites. Trial holes and a service scan before you launch are worth the time. Tell us what you know about the ground and we will tell you whether moling is the right method for it.

What Size Impact Mole Do I Need?

The mole has to be bigger than the product going in, so that the bore stays clear of the pipe and there is no drag on the pull. As a rule, allow around 30% over the outside diameter of your pipe or duct. A 45mm mole, for example, lays pipe up to 32mm.

At the bottom of the range, a 45mm mole lays product up to 32mm; at the top, a 180mm mole takes product up to 125mm. See the Specification tab for exact dimensions, including the maximum product diameter for every size we hire, along with lengths, weights and air requirements.

If your product sits near the top of a band, or you are pulling a jointed or collared pipe, go up a size and talk to us first.

Benefits of Impact Moles

• Sizes from 45mm to 180mm, laying product up to 125mm
• Up to 20m bore length
• One entry pit and one exit pit, so the surface in between stays as it is
• Forward and reverse, so the operator can retrieve the tool from the bore
• Bull nose reverse towing compatible
• A wide range of towing heads for pulling pipe in behind the tool
• Cheaper to run than the other trenchless methods

What Comes With Impact Mole Hire?

Every mole comes with the kit needed to launch and run it: optical sights and a ranging rod for lining up the bore, a safety launcher with pins, a lubricator and air hoses. Mole oil and antifreeze mole oil are available as extras.

You will need a compressor, sized to the tool. We also hire towing heads for pulling pipe in behind the mole, and trench boxes and shoring equipment if your entry and exit pits need support.

Common Questions

Nationwide Mole Hire

We hire and sell impact moles for sites across the UK, from fully equipped depots. If you are looking at an impact mole or any of our other trenchless technology for your next project, our trenchless equipment team can advise on the tool, the size and the accessories you will need. Find your nearest depot.