While shallow coal mining has pretty much ceased as an industry, historic mine workings (both recorded and unrecorded) litter large swathes of the UK potentially causing issues for construction and development projects.
Recorded mine workings are usually identified during a Phase I Desk Study and then confirmed during the ground investigation. Unrecorded mine workings can be more troublesome to locate although our extensive experience of coal fields means we can often predict where mining was likely to have taken place.
One recent example of this was a residential development site in South Derbyshire. A longstanding Client came to us and asked for a review of a study undertaken by another company. Using our specialist knowledge, we concluded that a significant thickness of soft strata recorded at shallow depth could be indicative of void migration from shallow unrecorded mine workings.
The team subsequently undertook some probing drilling across the site and confirmed the presence of old coal workings at shallow depth (10-15m below ground level) which were grouted on a primary 6m treatment grid with secondary holes on a 3m grid and tertiary check holes. An unrecorded mine shaft was also discovered which required further investigation and a bespoke treatment plan.
The shaft was filled with gravel in line with CIRIA C758 (Construction Industry Research and Information Association abandoned mine workings manual). It was then pressure grouted using three treatment holes to ensure all the voids were filled and prevent subsequent collapse.
In addition to foundation design, the GRM Design Team also designed a shaft cap which was approved by the Coal Authority. This was installed at rockhead which was around 3m below ground level. Our Site Inspection Team were on-site to oversee and approve the final phase of the installation.
GRM has a wealth of experience and expertise in the mining sector, indeed it is something of a specialism given the background of the two founding Directors. We continue to work with a range of clients from large commercial developments to private homeowners looking to build or extend properties.
If you have any development or construction projects, then please get in touch to find out how we can help save both time and costs. Please use your main point of contact at GRM or for new enquiries email firstname.lastname@example.org or call 01283 551249.