Dissolution Features Cliveden
Background
The site, which extends to about 6ha, comprised a former hospital which wasto be redeveloped with 2-4 storey blocks of residential properties, including one block with semi-basement garages.
Geological records indicated the site to be underlain by Winter Hill Gravel, (a Lacustrine delta gravel), over Upper Chalk, with a possible area where the Lambeth Group may overlie over the chalk beneath the gravels. There was precieved to be a risk from solution features on the site.
Investigation
Southern Testing undertook the detailed site investigation, comprising a geophysical survey and dynamic probing for dissolution features, followed by a second phase of probing where anomalies were encountered. Some trial pits were also excavated.
The soils encountered comprised sand and gravel, with some clay and gravelly clay in places, over chalk.
Recommendations
Areas of probable dissolution features were identified. The extensive probing also found localised loose zones in the sands and gravels and zones of softer clays.
Recommendations made in order to achieve the required design bearing capacities inculded:
- Compaction grouting of deeper loose zones in chalk
- Vibrocompaction of shallower loose zones in gravels
- Reinforced Foundations
- Borehole soakaways used for disposal of surface water runoff to reduce subsidence risks.
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