South Wales has a long history of coal mining activity which has left a legacy of potential hazards associated with former mine workings, whether that be mine entries such as shafts or adits, or from shallow mine workings of coal seams and roadways.

Quantum has an unrivalled heritage in the investigation, design and treatment of mining related hazards both in South Wales and in the rest of the UK.

The surface stability in areas of former mining activity is affected by the condition and size of the mining feature and by the strata in which they occur. In the case of mine shafts, when the mine was abandoned the shaft was either filled with local spoil from it’s base or perhaps some plug formed within the shaft, or capped with some form of cover. This could take the form simply of steel girders or rails with tin sheeting, or a concrete cap, which may then be back-filled over. Instability arises when either the capping gives way or deteriorates, or the wall lining the shaft gives way, allowing the overlying strata to “run” into the shaft resulting in subsidence at the surface. Old adits may be backfilled or capped in a similar way, but the risk of subsidence is more commonly concentrated around the entry.

Underground shallow mine workings can also lead to collapse of the ground above the roof of the coal workings or associated roadway. If old workings are left unsupported or deterioration of the pillar support left in place when the mine was abandoned, the stability of the strata above such workings is dependant on the strata forming the roof. Collapse of the roof can propagate to an extent that will cause subsidence at the surface, causing damage to buildings and infrastructure.

In either case the need for stabilisation is required when such a feature is present on a site where either development is proposed within an influencing distance or where a collapse has occurred.

Quantum are able to design and implement a programme of treatment for all aspect of hazards associated with former mining activity. This may include:

• Investigating the presence of shafts, adits or shallow mine workings
• Drilling and proving the depth and competency of fill within a shaft
• Pressure grouting the fill within a shaft to ensure its stability
• Forming a concrete plug within a shaft to maintain the integrity of the shaft wall
• Construction of a reinforced concrete shaft or adit cap
• Proof drilling over development footprints for shallow workings that affect a development
• Drilling and grouting shallow workings with a cement-pfa grout to fill voids or collapsed ground
• Dealing with mine gas emissions

Quantum is able to assess the risk to a site or development and work with Clients to achieve a bespoke solution to allow an economic way forward in addressing any mining hazards, all to Coal Authority approval and standards.