Client: Homes & Communities Agency and Cornwall Council
This project encompassed the geotechnical ground investigation, stabilisation and structural remediation of historic mine collapses associated with Troon Adit, Cornwall.
Troon is a large village located just over two miles southeast of Camborne in West Cornwall. The village is associated with the regions historical tin and copper mining industry that dominated the area in the 1800s.
JGP were initially employed to investigate and monitor ground subsidence, groundwater flooding and structural movement in several of the village’s residential properties. The problems were a consequence of collapses of an historic underground tunnel known as ‘Troon Adit’. The adit is a 1870s shallow water supply conduit. It was partially formed along and connected to the extensive historic shallow mine workings in the area.
Since the early 1980s, collapses within the adit resulted in the destabilisation five properties (resulting in several being condemned). The collapses also impeded water flow resulting in rising groundwater levels, flooding and rising damp in other properties. More than 100 houses were at risk from subsidence, structural damage and flooding as a result of the collapsing and blocked adit.
Remediation works to the adit were funded by the Homes & Communities Agency and Cornwall Council. Cormac was the Principal Contractor.
As Principal Designer, JGP provided:
- geotechnical ground investigation and ground engineering expertise for the adit remediation; and
- structural design of temporary stabilisation and permanent remedial works to damaged buildings.
The geotechnical and civil engineering services included adit inspections and design of adit stabilisation and reinforcement works. A total of 14 mining features were stabilised; and 775 tonnes of silt was cleared from 275m of the adit. The adit was strengthened using 70 tonnes of sprayed concrete. In addition, new drainage was designed comprising 120m of new low-level drainage, which was directionally drilled and a newly constructed low-level outfall that restored drainage and lowered groundwater levels.
The temporary works designed by JGP included the propping internally and externally of structurally unstable dwellings. This facilitated the permanent stabilisation works, which included foam injection techniques to stabilise the ground, piled cantilever underpinning to walls, and Helifix stitching of party walls and façades. Five damaged properties were reinstated, which included returning two of the condemned properties to habitable use.