Drill makes deep impact

Technically, it is boring. The two Van Elle drillers are carrying out site investigation which involves digging four boreholes through the London Clay beneath the platforms. They’re on their second, and each takes about seven days.

But apart from the constant activity of drilling, taking samples, testing, making records and keeping the machine running, the two men are breaking new boundaries on this job. Their tiny drilling machine, custom-made by Van Elle, has gone down to a depth of 30m, further than it’s ever managed before.

‘This is a hell of a machine,’ says Doe. ‘I have been drilling for a long time so I know. To get down to this depth with this machine is like doing 200 miles an hour down the motorway in a Mini.’

The original brief was to bore down to 25m, at which depth rock was expected. But the drill kept going and so, on instruction from the client, Doe and Patterson did too.

The machine was conceived for jobs like this. It came to site through a double door and down a flight of stairs: a major feat in itself. Just 780mm wide and weighing 2.5t, Van Elle designed and built the baby borer, which it has named VeTrak. Doe was one of three Van Elle employees involved in its development throughout 2004.

It started work in 2005 and has been busy ever since. Now Van Elle has plans to start manufacturing and selling VeTraks, says group marketing manager Kelly Herrick.

The tracked rig has been set up to a height of just 4m for this job although it can go up to 6m to allow sufficient clearance below overhead cables which must be avoided even though the shed is not in use. The VeTrak takes around half an hour to set up, and can be moved easily if necessary for example if the drill hits an obstacle.

Beside the rig are the samples of clay: long columns, known as U100s (U stands for undisturbed) will be tested for strength in a laboratory, while smaller pellet-like pieces called SPTs (standard penetration tests) are tested on site. The results will inform the foundation design for the building although no one can say yet what it is.

An added complication is the possibility of finding unexploded bombs during the investigation. Explosive ordnance disposal engineer Mark Wilson, of specialist firm Bactec, is on hand with a high-strength metal detector which he uses at certain points to avoid disaster. According to Wilson, if they do come across a bomb the most common course of action would be to leave it alone, since the disruption caused by removing it would be immense.

Van Elle’s client for the £15,000 contract is Costain, which in turn is the groundworks contractor for Laing O’Rourke.