Our team successfully demonstrated to the Coal Authority that ground movements and structural damage to an established commercial building were the result of subsidence from underground coal workings, rather than due to soil settlement. This resulted in the remedial costs being met and implemented by the Coal Authority.
A commercial premises in Beddau in Rhondda Cynon Taff had stood for around 50 years without any evidence of structural damage. However, in 2017, it started to suffer such severe structural distress due to ground movements so that some rooms became unusable. Being located in a past coal mining area, the Client had made a mining subsidence claim to the Coal Authority, who rejected the claim on the basis they believed the movements were not mining related.
We undertook a desk study review of the available information, including records provided by the Coal Authority and, from the Conceptual Ground Model generated, concluded that there was enough evidence that mining subsidence may be occurring to warrant more detailed intrusive investigation. We undertook angled and targeted, rotary cored boreholes and identified the 1.8m thick No 1 Llantwit coal seam along with voids, poor ground and abnormal groundwater at 7.5m depth below the surface.
We correlated the investigation findings with available records from an adjacent drilling and grouting scheme, and concluded that the ground conditions identified in the drillholes were backfilled underground coal workings and likely to be the cause of the ground movements and structural distress. A former mine shaft was also identified beneath the building.
Recommendations for risk mitigation measures were provided to the Client and the Coal Authority, who subsequently concurred with our conclusions and accepted the damage was the result of mining subsidence and validtaed the claim.