Preliminary Assessment – Ground and Water’s Preliminary Assessment was that the “relic alluvial soils” had been mis-identified and they may well have been Weald Clay Formation deposits. Additional investigation was required to attempt to delineate the spread of the alluvial soils and to determine the presence or otherwise of reworked soils of low bearing capacity.
Ground and Water’s Approach – Intrusive investigation comprising a number of machine excavated trial pits was undertaken to further prove the geology. Shear vane testing was undertaken at 0.50m intervals to determine the strength of the materials encountered at any one point. Further geotechnical classification testing was also undertaken.
The Outcome – Based on the results of investigation it was revealed the “relic alluvial soils” were actually restricted to only a small portion of the site. The client’s architects and structural engineers were advised that foundation depths and widths could be reduced, for most of the dwellings on the development. This case study underlines the importance of arriving at conclusions that result in precise advice in a timely manner. Had Ground and Water not been asked for a second opinion, the cost of development would have been significantly higher, in terms of materials, labour costs and time.