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Cornwall Desk Study Site Investigation Saves Developer Money !

Let Geoinvestigate’s Reading Office provide you with a quote for your next engineering geological, geotechnical or geo- environmental investigation in Cornwall including the towns of Plymouth, Exeter, Torquay, Barnstaple, Taunton and Newquay. If you require advice on a ground investigation, Phase 1 desk study or a borehole site investigation please contact our Reading Office for technical assistance, a chat about your requirements or a no obligation quote.

From Darren Bennetts Building Developments, Saltash, 2nd June 2015

“PS – Thank you for your assistance, the level of service I have received from Geoinvestigate’s Reading Office has been nothing short of outstanding and if I can put further business your way in the future then I certainly will”.

Partially excavated site at time of Phase 1 desk top study investigation
Partially excavated site at time of Phase 1 desk top study investigation
Saltash Formation. Sub-vertical, extremely close cleaved siltstone.
Saltash Formation. Sub-vertical, extremely close cleaved siltstone.

After being advised to carry out a very expensive geophysical survey to establish the ground conditions at a site in Saltash, Cornish developer Darren Bennetts asked Geoinvestigate for our opinion on what we considered was the right way to evaluate the engineering geology of this site.

Without visiting the site Geoinvestigate was able – with the aid of several photographs sent to us by Darren and a Google Street View traverse down the nearby Tamar Tunnel approach rock cut  to establish with confidence that rock head was likely to be present at very shallow depth below the site. This was important because a contiguous pile wall was to be installed to support the adjacent highway before excavation of the site was continued to its full depth.

Because the orientation of the cleavage at the site and in the cuttings of the nearby tunnel were the same it was fairly certain that the very limited snippet of siltstone exposure at the site was probably in-situ rock.

Subsequently on the basis of a brief desk study the developer was advised by Geoinvestigate’s Reading Office that a geophysical survey was wholly inappropriate on this occasion and in Geoinvestigate’s opinion a complete waste of money. Instead Geoinvestigate recommended a much cheaper site investigation option including the excavation of several shallow trial pits and mini boreholes to confirm bedrock levels across the site, especially in the critical area of the pile wall.

Understandably the developer required convincing that Geoinvestigate could provide the information he needed for a fraction of the cost of a geophysical survey. This was achieved by Geoinvestigate with the aid of a simple sketch of the site showing the information on the ground conditions that could be gleaned from Darren’s photographs and the nearby historical borehole logs.

Sketch of site showing initial desk study data and later exploratory holes
Sketch of site showing initial desk study data and later exploratory holes

 

Rather than carrying out additional expensive deeper rotary diamond drilling to 20m and recovering rock core samples, the nature of the rockmass conditions below the site was established by Geoinvestigate Reading using nearby historical borehole logs dating back to the 1980s. These long forgotten boreholes had been sunk close the property as part of the extensive site investigations for the Tamar Tunnel and its deep rock cutting approaches.

The 1980s borehole logs showed remarkable consistency and similarity – so much so – that Geoinvestigate were able to persuade Cornwalls Councils appointed highways checking engineer with considerable confidence to accept this existing borehole information as part of an AIP instead of drilling new boreholes. Acceptance of the historical borehole logs by Cornwall Council resulted in considerable further cost saving to the developer who was delighted with the outcome.

The AIP was submitted by Momentum Civil and Structural Engineering Consultants of Bristol working in close collaboration with Geoinvestigate’s Geotechnical and Geo-environmental Office at Reading and Bristol based Gemech Piling Specialists.

As far as Geoinvestigate is aware this is the first time Cornwall Council has accepted technical information contained in old borehole logs in an AIP of this nature.

Geoinvestigate’s Reading Office provides engineering geological, geotechnical and geo- environmental services to Cornwall including the towns of Plymouth, Exeter, Torquay, Barnstaple, Taunton and Newquay. If you require advice on a ground investigation, Phase 1 desk study or a borehole site investigation please contact our Reading Office for assistance or a no obligation quote.