Safety works have been completed by the Mining Remediation Authority to protect residents in Arley Lane, Wigan, from ground collapses caused by a historical coal mine shaft.
Our teams designed a permanent solution, pouring more than 120 cubic metres of concrete in one day to form a 0.5-metre thick, heavily-reinforced, high-specification cap with a diameter of 16 metres over the shaft.
Overview of the main cap area from the north.
The authority has records of mining in the area as far back as 1840 and Malcolm Scott, regional project manager for the public safety and subsidence team, said
There were a few challenges to this project. We couldn’t excavate deep enough to place the reinforced cap on the upper surface of the bedrock due to the constraints of the garden and extensive tree removal that would have been required. Therefore an oversized octagonal cap was constructed, 2 metres below ground level, to cover a collapse zone of around 13 metres.
As Arley Lane is single-track we had to bring in compact concrete mixer trucks, about half the size of the vehicles we normally use, and we also had to pour a temporary layer of thin concrete to give access to the site during the construction phase.
Finally, a big thank you to the community, who have been helpful, co-operative and patient throughout the duration of the works.
Malcolm Scott, of the Mining Remediation Authority’s public safety and subsidence team, at the site.
A minor collapse near a recorded mine shaft was first reported in December 2018, which was excavated and filled with stone in January 2019. The site was then monitored and works were needed again following more ground movement in April 2019.
The area then appeared stable until July 2021, when there was a further minor collapse. Ground investigations proved there was a 3.5 metre diameter shaft, which had been plugged with concrete between 4.5 metres and 6 metres below ground level by the National Coal Board in the 1970s.
The drilling also showed that solid rock – known as rockhead – was around 11 metres below ground level, allowing clays and looser material to migrate into the shaft beneath the plug, so a resin grout injection was used to try to stabilise the ground, but further loss of material was reported in May 2023, which meant the new cap was needed.
Following the latest works, the area has now been backfilled to create a soil base and site demobilisation will start this week, leaving only turfing and landscaping works for 2025.
As part of our work to keep people safe and provide peace of mind, you can report a coal mine hazard to us, 24 hours a day, 7 days a week, by calling 0800 288 4242.
The main cap from the south.
