Miller Homes Ltd
Shallow coal seam borehole investigation
Investigate the risk presented by suspected shallow coal workings on the site of a proposed housing development and supervise remediation work
The former Chesterfield RUFC ground at Sheffield Road, Chesterfield lies within an area affected by historical coal mining i.e. a Coal Referral Area. A previous report designed to facilitate the divestment of the site concluded that ground instability associated with shallow coal mining was unlikely. GeoDyne advised the prospective site purchaser that in our expert opinion, the area was potentially prone to shallow coal workings and hence instability and we were subsequently appointed to investigate the site in more detail.
Our desk study confirmed the presence of mine shafts and the likelihood of shallow seams near the surface. In consultation with the developer, we designed a programme of borehole drilling in line with industry good practice.
The drilling revealed voids and probable collapsed workings confirming that the coal had been worked and that this historical shallow mining represented a potential risk to the development.
Our report confirmed the need to stabilise the site and made recommendations regarding the design of foundations for the proposed buildings.
Our flexible approach and phased investigation delivered substantial savings to our client.
The extent to which coal workings can affect the stability of the ground can be determined by a number of factors. A traditionally worked coal seam represents a limited risk provided that it is overlain by a sufficient thickness of competent rock cover, typically greater than ten times seam thickness.
On this site the, rock cover rarely exceeded five times the seam thickness.