Impact Moling

In Dentdale there were about 40 road crossings involving the impact mole. This is done by a specialist employed by B4RN, you would normally get Nick Hall to advise you on road crossing locations. You don't really have to get too involved in the operation, but if you understand the procedure and the sort of thing the mole can do then it helps with planning.

It takes half a day to do one crossing if it goes reasonably well.

At its simplest -

Just dig a hole either side of the road, about 3 foot deep and 5 foot long
Aim an impact mole from one hole to the other
Let it chug away like a hammer drill under the road for 10-100 minutes until it appears

Only once was there a failure to get under the road, in that case we eventually crossed the road by a different method 400m away from that point, so it makes sense to have the road crossings done well in advance as they can affect the whole duct route.

A volunteer should be around for this operation

To liaise with the landowners
To general assist (you need someone either side of the road on occasion). And a bit of traffic management is always good publicity as you end up talking to everyone who goes past. (Some rule says you are ‘not allowed’ to traffic manage. Okay, don’t do it on the A6.)
You may want to tie in the operation with getting the orange duct through. The guy doing the moling just puts a conduit in the road for you, fiddling with the orange stuff is your job.
To learn the operation so you can better plan and locate future road crossings, so you understand the capabilities of the process and where best to use it. (It also works under tracks and hedges for example)
To seize the opportunity of a digger being available. A large hole is being dug next to a road, you could get a chamber put in here at not much extra effort or cost.
For changes of plan requiring local knowledge. For example – we are having trouble getting under the road here, would it be okay to try a bit further along from that field?

What can go wrong?

· He can’t get through because of rock, so you re-route and think of another place where you could get through. If you have this plan already, then the moler could well be able to try this immediately, otherwise you will have to re-book him. If you are set on this particular way across then if it really came to it, you could get the tarmac cut open and do it that (expensive) way. In that case B4RN would get interested and probably find you another way of solving your problem.
· He hits a BT line or something in the road. The advantage of calling in a professional is that it’s his problem, and he has probably done it before, so he knows what to do. Assist. Be concerned. Knock on a few doors. Apologise.
· Apparently in rare cases the mole can start turning slightly up and start to crack the tarmac or to start bending the whole road upwards. Apparently you are aware of this possibility and notice the signs very early on and turn everything off in a panic before any real harm is done. The after-effects of this are un-noticeable and no harm is done, apparently.

The Procedure

That’s the whole set-up. Left to right. Car with spare tube on top. Can of spare diesel. The silver pole is the sighting rod. Spade. Digger. Man peering down hole. Hole with long pipe leading back from it to blue ‘oiler’ and back to the compressor. Two digger buckets near the compressor. Road behind the hedge.

Firstly think it all through.

What services are there - especially any that are inside the road, others can be located by digging
What height difference is there between the sides?
How much space is there to work on either side

This determines where you cross, how deep you must dig and in what direction you will drill. You will also be looking round for clues as to what the ground may be like.

Dig a hole either side of the road, exactly opposite each other. Go down to the same horizontal level, so that the shallowest trench is about 1 metre deep. You make a trench half a metre wide by 2 metres long

Setting up slowly and methodically.

The silver cylinder is the mole. It is heavy. It is driven by compressed air along a tube to a compressor. This drives the point of the mole to act like a hammer drill and peck its way through the ground under the road. The blue thing adds oil to the proceedings. Take some time lining up the angle of the mole to aim for the hole you have dug on the other side of the road.

The mole has been set off half a metre. It appears to be heading too far up, so a sling is attached to the back of the mole to pull it up. The vertical silver thing is the sighting rod to see if the aim has now been corrected or if further adjustment is necessary.

If the mole had been aiming too far downwards, then the digger bucket would be used to press down on the mole.

This is the hole the moleman (Steve) is aiming for. That's the corner of a bridge over a river, so there is not a lot of room for error.

And if all goes well, the mole pops out the into the pre-dug hole. The mole is usually pulled out through this hole. It has been dragging about 6 metres of 75mm ducting behind it which is left under the road, ready for the orange ducts.

The whole operation. A farm track involves the same procedure, but it's usually a a lot easier as you have better access to both sides.

That moment when the impact mole appears from under the road.

Note the action of the mole. It grips by friction along the sides and from the mass of body being far greater than the hammer tip. Once the mole is out of the soil it stops itself because the sides have no grip anymore

Moled road crossings should really be done before any ducting is laid., not left until last.

Road crossings are difficult and the guy doing it needs a bit of leeway to decide himself exactly the point which will give him the best chance of succeeding.

The last thing he wants is to have a ton of orange ducting left everywhere exactly where he wishes to dig.

And there is always the possibility that the road crossing cannot be done there and has to be 50 metres up the road.