Building Around Mine Shafts

Background

Historically, mining has played a significant role in the UK’s industrial history. Coal mining in the 19^th century was heavily dominated by Yorkshire, Lancashire, and the East/West Midlands, with regions across Wales and Scotland also seeing major activity in the 20^th and 21^st centuries. Meanwhile, tin and copper mining across the country has been synonymous with the South West, namely Devon and Cornwall, since the Bronze Age.

Although the UK mining industry is now strictly regulated, this was not always the case. Before legislations such as the Mines and Quarries Act 1954 and the Mines Regulations 2014, there was limited oversight of working conditions, site safety, and the proper management of abandoned mines. This historical lack of regulation has left the UK with over 400,000 abandoned mine entries, posing ongoing challenges for today’s construction industry.

What are Mine Shafts and how can they affect my Project?

Mine shafts are vertical or horizontal passages that provide access to underground mines. When a mine is no longer in use, these shafts are typically backfilled to stabilise the surrounding ground and prevent future subsidence. However, this was not always standard practice, and many historical mine shafts were abandoned without proper backfilling. As a result, developments on land containing unrecorded or poorly treated shafts can face several risks, including:

• Subsidence and Structural Collapse – Building on ground containing voids can result in inadequate support, leading to localised foundation failure or differential ground movement caused by poor compaction. These issues may cause cracking in walls or, in severe cases, complete structural collapse.
• Hazardous Gas Emissions – Abandoned mine shafts can act as pathways for odourless gases such as carbon dioxide, carbon monoxide, and methane. These gases can migrate to the surface and accumulate within buildings, creating risks of fire, explosion, or suffocation.
• Safety Risks for Construction Workers – Personnel working on sites with a history of mining activity may be at risk of falling into inadequately covered or unrecorded mine shafts.

Engineering Solutions to Treat Mine Shafts

Given the risks associated with construction on historic mining sites, structural engineers must consider the presence of abandoned mine shafts in their designs and incorporate methods to mitigate ground stability hazards. A comprehensive site investigation is essential to identify possible shaft locations, assess ground conditions, and determine the measures needed to ensure safe and stable foundations.

Common mine shaft remediation techniques include:

• Shaft Fillings – This method involves stabilising and sealing mine shafts using cement-based grout or granular materials to eliminate voids and prevent ground collapse. Fill materials should be chemically stable, resistant to acidic mine water, and free from metal fragments or combustible organic matter.
• Shaft Plugs – An engineered shaft plug provides a durable barrier at a specific depth, often at or below rockhead, to prevent inward collapse, gas/water migration, and sudden subsidence. Proper design accounts for lining failure, water expulsion, air pressure changes, and settlement of the fill material.
• Shaft Caps – Shaft caps create a secure barrier over mine shafts, preventing unauthorized entry, controlling hazardous gas emissions, and stabilising surrounding ground. Vertical shafts typically use reinforced concrete slabs anchored into bedrock or supported on piles reaching competent soils, while horizontal adits requiring occasional access often use steel plates or grates.

Our Expertise

With hundreds of projects across Devon and Cornwall, we at Harban Redwood have extensive experience in addressing the challenges of building on historic mining sites. We have helped numerous clients strengthen existing structures and futureproof new developments to ensure long-term safety and stability.

If your project is located in or near a historic mining area, our expert engineers are ready to provide tailored guidance to safeguard your building and minimise risks. To arrange a consultation or learn more about how we can assist with your project, please contact us at info@harbanredwood.com.