3D geology modelling enables new development to mitigate past mining risk
St Austell in Cornwall has a long history of mining and is home to the world-famous Eden Project which is built within a former opencast China Clay mine. It is also the focus of new mining ventures for the extraction of Lithium, an essential component to long lasting batteries which will power the electric revolution.
The multitude of deep pits and unmistakable conical spoil tips provide a clear reminder of the impact of china clay mining in the area. However, now hidden from sight and often lost to memory is the legacy of the hundreds of years of metalliferous mining, mainly for the extraction of tin and copper.
Historic Ordnance Survey mapping along with abandoned mine plans provide snapshots of the past mining activity which has dominated the area at periods throughout history. However, this is often only a fraction of what took place underground and leaves much of the early activity completely unaccounted for.
A comprehensive understanding of the risks relating to the legacy of non-coal mining activity is essential for the multiple large residential and commercial developments which are proposed in the local area.
The site history challenge
Image of the area around the Cuddra Mine, near St Austell in 1882; below overlaid with Mine mining activity and shafts.
A new development of some 200 residential units was proposed in what appeared to be a “green field” site to the house builder. Knowing that historical mining had occurred in the local area, we were approached to assess the potential risk to the site.
Very often, the first line of evidence in assessing mining risk to any site is to study the historical records. This may comprise various mine abandonment plans of varying quality and reliability, along with any historical Ordnance Survey plans. Each of these are carefully studied and compiled to provide a history of the site through time.
However, such plans can often be misleading on the true extent of historical mining activity. They represent a snapshot in time and show a fraction of the mining activity which may have occurred. An initial desktop mining search conducted on the development site would have revealed four recorded historical mine shafts, which were already shown as “old shafts” by the late 1800’s on the Ordnance Survey Plans.
Mine plans of a similar age show extensive mining for Tin and Copper continuing hundreds of metres underground to the north and west of the site but also show no significant activity at the development site. The initial groundworks unearthed multiple unrecorded shafts and shallow mine workings, so it was clear that the site history was more complex than the available records indicated.
Taking a deeper view
We undertook multiple phases of investigations across the site which required the full resources of our geology team. Once we had built a sufficient surface and subterranean profile, we created a bespoke and comprehensive 3D ground model of site, revealing the location of over thirty previously unrecorded mine shafts and a complex network of shallow underground mine workings.
The above image shows the mining features projected in their exact X,Y location in relation to the development layout plan. Because the site plan is 2D and 2D, the mining features are projected with their actual elevation hovering above. The red cylinders are shafts, with grey areas showing where they have been concrete filled as part of the remediation. The larger brown area is the edge of a larger excavation, so the developer could see what it was affecting.
The site can also be visualised by an animated fly through of the 3D model:
The 3D ground model was shared “live” with our client as the investigations progressed. It was georeferenced and to scale, so that the effect of mine workings could be easily viewed in relation to the proposed site layout – a powerful tool to visualise the scale and potential impact to units above ground.
Benefits to the client
This enabled our client to adjust their build program so that the high-risk areas could be initially avoided to allow for construction and sale of plots in unaffected areas. Remediation could then be focused on appropriate areas enabling the construction across the site and resulting in significant cost savings.
The project underlines how our approach provides and unrivalled understanding of mining risk. The combination of site investigation data, 3D ground modelling and our comprehensive suite of historic Ordnance Survey mapping is matched to paper geological plans and historic land use data. This means that conveyancers and their clients, developers and architects can be confident that an analysis of historic mining risk will be thoroughly investigated, risk mitigated and can enable transactions or site appraisals to proceed with confidence.