We recently undertook a ground investigation near Marlow, Buckinghamshire along the southern edge of the Chiltern Hills. A Phase I and Phase II Investigation was required for a proposed commercial site on undeveloped land.
The Phase I Desk study indicated the site is underlain by the Clay-with-Flints Formation (a chalk residual deposit) overlying the Newhaven Chalk Formation (formerly the Upper Chalk). For areas where chalk bedrock is underlying the surface there is a possibility of a significant geohazard termed solution features which can take the form of dissolution pipes, sinkholes and swallow holes. Various factors including: type of chalk, topography, groundwater level, strata overlying the chalk, periglacial and glacial history should be assessed when undertaking a risk assessment of dissolution features. This risk assessment identified a moderate risk of solution features on site and therefore required further assessment during the intrusive works.
To target this potential geohazard the intrusive works included window sampler boreholes and super heavy dynamic probes down to 10m bgl and trial pitting. The intrusive works enabled us to identify two distinct in-filled dissolution pipes on site which were in-filled with the Clay-with-Flints Formation. As such careful measures were recommended to limit the reactivation of solution features on site including the suitable distance of SUDS on site from any structures with foundations and roads.
Identifying solution features on site is relatively cheap when compared to the costs of correcting developments affected by subsidence. Geo-Integrity can deliver the appropriate advice in a timely, cost effective way to mitigate the impact of solution features on site. Please contact us on info@geo-integrity.co.uk or 01280 816409.
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