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ON TRACK FOR CHANGE

SITE INVESTIGATION - Roman era technology is getting a 21st century makeover.Damon Sch³nmann went to Derby to see its first site test.

'If it ain't broken don't fix it, ' goes the old saying, and there are some things that have worked so well for so long it certainly sounds like sensible advice.

But an equally true expression might be 'engineers will always tinker no matter what' and few things are left for long without getting improved, modified or generally messed around with.

The cable percussion rig is an example of something that, aside from component materials, changed very little for perhaps a couple of thousand years until the arrival of the internal combustion engine to power the winch. Rigs have in all probability been towed and dragged to position at site, or built on the spot, since the earliest contraptions were invented.

So a rig developed by contractor Van Elle has been turning heads at the Shardlow gravel pit, operated by Hanson, 8km south of Derby in the East Midlands. The machine is being trialled making boreholes alongside a traditional Dando 2000 shell and auger rig in ground comprising topsoil over sands and gravels over marl.

'We saw people toiling with an old style rig that has hardly changed from Roman times, with slaves pulling a rope, and we thought we must be able to make something better, ' says geotechnical services division director Andrew Johnston.

The gap in the market is with window sampling, he says. 'You often come up against obstructions that you can't get through but you could with a shell and auger. So we wanted the restricted access strengths of a window sampling rig and the [penetration] strengths of shell and auger.' The cut down shell and auger rigs on sale are slow and awkward to assemble as well as needing the potentially dangerous assembly of heavy components, he says.

Fitter Graham Beardmore explains: 'We had an old tracked machine in the yard and I could see we could use it to make a small rig.' Johnstone called his bluff.

The result is the 2.5t Vetrak, a tracked cable percussion rig that in transport mode measures 1.9m high, 780mm wide and 2.8m long, meaning it can fi through a doorway.

It assembles hydraulically to 6m tall when in position and can also operate at a reduced 4m height for restricted headroom work. The rig is transported to site in a modified 10t box lorry with a string of casing.

At the time of GE's visit, lead driller Glen Doe was putting the machine through its paces. He pointed to the Dando 2000 saying: 'These old shell and auger rigs have been going for ever and a day and nothing can touch them at what they are intended for. But you can't get on to garage [petrol station] forecourts and tight access areas.' This is where the new rig's lower 4m height comes in. A heavier sinker bar is used to make up for the reduced drop height.

Van Elle sank five gravel pit boreholes up to 15m deep and installed 50mm diameter monitoring wells in three for environmental consultant Egniol. This soil profile and groundwater monitoring project is looking at the depths of the underlying clay and its suitability for engineering purposes before possible extraction.

The scheme meant the Vetrak could drill its first onsite borehole from start to finish. 'It seems to be doing everything it is supposed to, ' says Beardmore. 'These are two of the best drillers in the country and if they're happy then it will be one of the best machines in the country. It has a couple of very minor niggles at the moment like the shape of the soil emptying spike but we'll get it all perfect.' Before the company started down the development path it looked at what the market had to offer. While other companies have single mast rigs on tracks, Beardmore says they are much bigger than the Van Elle unit.

'The only rig that comes near this lightweight one is a Dutch machine that doesn't have its own engine and power pack on tracks. Instead, these are on a trailer and the rig can only go as far as its hydraulic hoses will stretch. Also, it can only lift 1t [compared to Vetrak's 2t].' Van Elle completed its £5000 contract in September.

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