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Video cone penetrometer testing equipment has saved potentially huge remediation costs on a site in the Netherlands contaminated by creosote.

A borehole site investigation found a 3.5m high contamination plume in the underlying sand.

However, when the video cone was used, the plume was found to be only 1.2m, with the remaining 2.3m attributable to crosscontamination during drilling.

Developed by GeoDelft in the Netherlands, the video cone has just been introduced into the UK by Lankelma CPT.

A small video camera mounted in the side of the cone, with a halogen light behind sapphire glass, records a constant image as it is pushed into the ground.

Lankelma CPT managing director Eric Zon said: 'The imagery gives a clear undisturbed picture of the ground with seven times magnification allowing you to see individual grains and colours of the material.'

Lankelma demonstrated the system on a UK site with large chalk solution features infilled by sand and gravel. Conventional CPTs were used to profile features up to 30m long, which will be grouted up to improve stability.

The video cone was used to confirm the depth of the contact between the sand and gravel and the highly weathered chalk, which is sometimes hard to distinguish using normal CPTs, Zon explained.

Results give an accurate indication of the amount of grout needed and, more importantly, reduce the danger of under-grouting and the risk of failure, he said.

'The video cone in conjunction with normal a CPT cone could be the future of site investigation, ' Zon added.

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