Case Studies Grassmoor, Chesterfield

Grassmoor, Chesterfield

Our brief

Lithos were initially commissioned to carry out a review of 3rd party data of a 7-hectare parcel of farmland, with a farmyard in the south-west.  The 3rd party desk study acknowledged the presence of a coal seam outcropping on, and underlying most of, the site, as well the presence of a mine entry in the north.  However, the 3rd party intrusive investigation found no evidence of either coal, or any workings.

Our desk study included review of abandonment plans for the Top Hard seam which showed ‘old workings’ in the south-west and ‘longwall mining’ elsewhere.  Lithos then supervised a further phase of drilling and found mineworkings which posed a potential risk to surface stability across c. 10% of the site’s area. In addition, a likely ‘bell pit’ was found in the south-west (close to the outcrop).  Risks associated with further, unrecorded mine entries (e.g. bell pits) were highlighted in our report.

Post-investigation, Lithos prepared a Specification for treatment of shallow mineworkings (including advice on treatment of mine entries) and provided supervision during treatment (drilling & grouting).  Using our knowledge, experience, and excellent working relationship with the Coal Authority, we were on hand to provide robust, clear advice in the face of significant mining-related issues encountered during remediation and construction, including the discovery of multiple unrecorded mine entries. Lithos provided technical support and guidance with respect to mine entry treatment that took account of each shaft’s location and the proposed housing layout.

The outcome

On completion of drilling & grouting and treatment of mine entries, Lithos produced a Completion Statement for each phase of work in readiness for submission to the warranty provider and local authority.

This site highlights the importance of a robust investigation, as the presence of mine workings was missed by the original, 3rd party consultant.  It also provides a good example of the issues posed by unrecorded mine entries, which are common on sites underlain by shallow coal.  Potential risks associated with such features should always be highlighted as part of the site’s appraisal, enabling contingencies to be put in place.

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