LOCATION: Wales, UK

• Site Investigation

• Coal Mining Risk Assessment

• Geotechnical Assessment incl. Foundation Design

Following calls from the Local Authority regarding future mining activity, the developer instructed South West Geotechnical to complete a coal mining risk assessment along side a detailed geotechnical assessment for foundation design.

Seams beneath the site to a depth of 270m have been the subject of historical mining, and for that reason this effectively sterilised zone would be of no prospecting interest to the mining operator.

Therefore, noting that shallower workings have greater surface impact than deeper mining, we considered that the shallowest possible target seam would be the first significant seam (1m thick or greater) below the sequence covered in the Coal Authority’s worked zone is at a depth of 330m.

An assessment was then made using the Subsidence Engineers Handbook.

It was concluded unlikely that the effects of multiple seams would impact on any one point immediately, unless their working faces were coincidentally vertically above each other. This is because the subsidence wave from an advancing face occurs almost immediately, with just small amounts of creep for a number of years thereafter.

However, following consultations with Neath Port Talbot County Borough Council, (NPTCBC) it was decided to assess the effects of all available seams being worked at once. NPTCBC also advised that a 220m wide longwall panel should be considered in the assessment.

On this basis, the degree and pattern of subsidence for each seam was assessed individually, with the cumulative effect of the seams being worked contemporaneously also been assessed. The predicted differential settlement was then plotted to ensure any resulting tilt at the base of the proposed turbines could be tolerated.

The tilt was then graphically illustrated and discussed in detail.

Critically, the assessment went on to conclude “This will ensure that the coal assets remain viable and that the proposed / licensed deep mining operations can proceed uninhibited. This would also mean that a mining exclusion zone is not required.” Thereby satisfying the planning obligations and allowing the developer to proceed with the development.