Site Investigation Solutions Open Day
7th and 8th June 2005
Co-hosted by Zetica, Lankelma and Norwest Holst Soil Engineering
Heythrop Country Park, Enstone Zetica Test Site
A very successful event was held at Zetica’s Test Site in Enstone over 2 glorious days. A total of 30 delegates from across the construction industry benefited from a range of presentations on recent advances in brownfield site investigation methods including; the Landsweep™ concept, bomb detection – separating fact from fiction, developments in cone penetrometer testing, intrusive SI methods and integration of surface and borehole geophysics, CPT and drilling.
This was coupled with discussion sessions and practical demonstrations allowing delegates to get a first hand impression on data acquisition techniques and results of data processing and interpretation.
The overall aim of the open days was to review technologies for optimising the cost-benefit of brownfield site investigation projects. The venue was apt in the context of known buried targets representing typical brownfield hazards and complex site geology.
Frank round table discussions on the perceived strengths and weaknesses of different SI strategies and methods were held. The views of consultants, developers and contractors were all aired and a consensus reached that consultants would be interested in regular briefings on evolving technologies to help them design more cost effective solutions to SI problems. Developers and contractors generally appreciated the value of having a wide spectrum of SI tools to choose from and were interested in reducing cost and risk.
 Lankelma and Zetica used the open days to launch a new tool for combining the search for UXB and mapping the maximum depth of UXB penetration / pile bearing layer. The combined Magcone-CPT tool, dubbed “Mag-CPT” can provide better value to clients commissioning a bomb search providing both UXB hazard detection and geotechnical materials characterisation in one survey. Find out more.
Other highlights included a case history on cost savings produced by combining borehole geophysics with drilling to characterise a contaminated site. Conventional methods of drilling to create a 3D geological section required 15 boreholes to be drilled to 15m depth. A 45% saving was achieved by using the Electrical Resistivity Tomography (ERT) method to define site geology and hydrogeology instead of the high-density drilling programme. Only 6 boreholes were needed because the ERT method investigates a much larger area away from the boreholes.
A discussion on designing effective surveys was extremely useful. Practical examples were given on the test site of how non-invasive surveys should be planned to solve a range of problems. What may work well on one site, can be ineffective on another due to differences in the burial setting. Limitations in published standards to measure low strain moduli using crosshole seismic geophysics were also discussed. Results from the test site were used to demonstrate the effect of local variations in geology on crosshole seismic data quality carried out to published standards, and the significant improvements in the results which are possible using crosshole seismic tomography.
The use of surface shear wave seismics to produce 1D shear wave velocity profiles with depth were shown to be accurate to within 15% of values derived from crosshole and downhole seismic surveys to depths of up to 15m below ground level in the local geological conditions (layered Great Oolite Sequence). This technique offers a cost effective alternative to borehole geophysics especially in ‘noisy’ urban settings where this surface method actually works best.
A challenge was put out to consultants to utilise boreholes and CPT tests in conventional investigations to better effect by combining them with either a site-wide surface geophysical scan to look for local anomalies to investigate and/or filling in the gaps between boreholes using borehole geophysical methods and sampling undisturbed ground using wireline geophysics. The result will be more value for the SI expenditure rather than necessarily increasing the SI budget.
The 'Site Investigations Solutions’ open days will become an annual event.
Our thanks go to Eric Zon, Lankelma Ltd and Digby Harman, Norwest Holst Soil Engineering Ltd without whose generous contributions, the event would not have been possible. I would also like to compliment the professionalism of our organizing team headed by Mandy Eriksen and Mike Sainsbury. Their efforts were exemplary.
Asger Eriksen
CEO, Zetica Ltd
 
Brownfield SI test site - Enstone
“Thank you for the informative day on Wednesday. I fear that I may not be allowed to come to the next one – I suspect that that privilege will go to somebody more senior next time!”
Neil Esslemont, Inspection and Assessment Engineer, Trans4M
“[The open day] was very informative. It was good to see how geophysics has moved on since I started out in the industry.”
Jim Twaddle, Principle Environmental Engineer, JNP Group
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