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Dangerous Depths: How 200 mines didn’t put a stop to one of Cornwall’s most ambitious development projects

Despite the golden era of mining long being consigned to the past, it’s still affecting the property regeneration and land development market, and none more so than in Cornwall which has been home to over 2,000 mines. Often left to rot and decay, abandoned mines leave behind a legacy of unstable ground, contaminated land and in the worst case, sinkholes – which often put a firm stop on any proposed development or regeneration plans. 

However, for the brave, historic mining doesn’t have to signal the end of a development project, and could instead be used as an opportunity to plan, design and construct intelligently, making the best use out of every inch of land. This was the issue facing the team behind the Hallenbeagle project in Redruth, an ambitious plan to create a new Bio Park – but with over 200 mine shafts, a history of sinkholes and arsenic contaminated land to contend with, the development wasn’t going to be easy. 

A new future 

Designed to support economic growth and regeneration in the area and located next to the main A30 route at Scorrier, Redruth in Cornwall, the Hallenbeagle regeneration project focused on investing over £8 million in transforming 12.5 hectares of land into 14,330sq ft of business, distribution and office space. The project was led by Hallenbeagle Estates Ltd, and also received match grant funding from the European Regional Development Fund. 

However, with the site once being home to one of the county’s most important copper mines, it was obvious the project wasn’t going to be a quick fix. Lying in a heavily mined area where extensive extraction for copper and tin had taken place for hundreds of years and throughout the 19th Century, available maps and plans only recorded a fraction of the historic mine workings present – with an estimated 200 mine shafts in the area. 

Mine workings commonly run long distances beneath the ground from mine shafts and extend beneath land that is due to be developed. Today, closed mines are capped and filled in to stabilise them and minimise risk, but old mineshafts were not always dealt with in this way. For the Hallenbeagle project, the effects of historic mining were already evident in the area with cases of sinkholes up to 300ft deep opening near homes and main road routes.

Plugging the problem 

Mining searches are vital in today’s property, construction and development market, and essential for determining whether there is any evidence of historic mining activity on an area of land. This is important even for locations where there are no obvious signs of mining, and while closed mines leave little evidence on the surface, they still have the potential to cause major problems – including putting a stop to construction plans. 

With an area of 34 acres to cover, Hallenbeagle needed to ensure the land was safe before any regeneration development took place, employing the expertise of Mining Searches UK to oversee the investigation and secure the hundreds of mine workings. Uncovering more information about the network of mines was an initial priority, and the team first carried out extensive desk research referring to all available archived records of the land, from historic archives and maps, to land surveys. 

Scratching the surface wasn’t enough and some of the larger identified mining features required further investigation, with the MSUK team carrying out a combination of drilling and site stripping. Geologists used this information to assess ground stability, as well as the risks posed to the development and neighbouring properties, digitising the information so developers could see the precise location, extent and features for each located mining feature. 

Where a mining investigation has confirmed the presence of mining features, an architect can also design appropriately to minimise the cost impact for a development. For example, siting a proposed dwelling away from a mineshaft can have a positive impact on foundation design, or for larger developments like Hallenbeagle, it can also potentially help with construction phasing of a site – as well as ensuring drainage runs and soakaways will not be affected by historic mines. 

Business benefits 

Taking five years to complete, today Hallenbeagle is home to the Cornwall Bio Park, a thriving hub of business and office space, with 23 building plots, fully serviced roads and infrastructure created for a variety uses, including waste recycling. 

As one of the county’s most complex, high profile developments for the area, Russell Dodge, Former Director of Hallenbeagle Estates said: “Understanding the finer workings of the land, as well as the potential impact of past mining activity was essential in delivering the project. By employing mining experts, we were able to understand the risks posed to development, helping us to plan effectively – ensuring not only the safety of workers, but also future occupants.” 

Although mining searches may often be considered an inconvenience, they are vital in detecting problems before they become larger issues in the future. By addressing at the earliest possible stages of planning and construction, developers can not only save time and money, but can also ensure that projects are designed around the best use of the land and are safe for all occupants in the long term.

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BDC 319 : Aug 2024