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  • Dave Calder

Oban Baptist Church

This week, we were up at Oban Baptist Church to perform a preliminary ground investigation in lieu of a potential redevelopment. We had performed some recent drilling works nearby at the harbour and encountered deep (7-8m) made ground deposits. Furthermore, published borehole records to the north and southwest recorded raised marine superficial deposits of significant extent, often of poor strength.

There was restricted access into the site and therefore we mobilised our smallest rig, a Archway Mini-Tracked Lightweight Rig windowless sampler. We also deployed our Continuous Surface Wave System (CSWS) which can give a indicative depth profile of low strain shear strength of the subsurface. This is also one of the several geophysical methods we undertake to identify rockhead position.

Although the anticipation was for these deeper, potentially soft/loose superficial deposits, it was clear after a quick recce of the local area that there were areas of outcropping bedrock in the vicinity. The windowless sampler rig was also encountering shallow refusal, and the CSWS results confirmed this. We managed to complete four borehole positions in the day, with four CSWS locations, and will be able to provide the client with a rockhead contour plan in order for them to develop a development strategy.

Lesson of the day: Always expect the unexpected!

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