Brownfield Commercial Development, Merthyr Tydfil
Introduction:
In a complex setting affected by both geological and anthropogenic factors, we have helped enable the design and implementation of large extensions to an existing commercial development. We were able to provide detailed, considered information to allow construction of the extension, minimising off-site disposal, incorporation of ground gas protection measures and sustainable drainage features. We were able to conclude that further investigation and/or treatment of coal and/or ironstone workings was not required resulting in a significant saving.
Details:
We were employed to provide an integrated Ground Investigation and Coal Mining Risk Assessment having been involved in numerous phases of this brownfield project including in an area of extensive industrial development, coal and ironstone mining and reprofiling as part of Welsh Development Agency works from the 1980s onwards.
Our Conceptual Ground Model suggested deep Made Ground, coal and/or ironstone extraction and potential obstructions associated with historical basements and demolished buildings.
Investigation work included trial pits, rotary coring, infiltration assessment for SuDS and ground gas monitoring. Detailed interpretive assessment followed including consideration of contamination, ground gas risks, mining hazards and instability caused by slopes and low quality/strength shallow strata.
Our Phase 1 Desk Study and Coal Mining Risk Assessment identified there was likely to be a significant impact on the development from ground hazards, including contamination, asbestos, ground gas, thick/poor quality Made Ground, and coal/ironstone mining (normal brownfield hazards in South Wales). The large historic Dowlais Great White Tip encroached into the south portion of the development area.
Investigation confirmed conditions that varied from the anticipated Conceptual Ground Model. We identified a thick cover of Made Ground and reworked superficial deposits to depths of 14m below ground level. Several thin coal seams (<0.5m) were identified at depth; however, no ironstone was recorded, nor was any evidence of underground mining.
The ground conditions varied due to the probable excavation of shallow coal and ironstone seams prior to the earliest available mapping (pre-1800s) as part of the extensive local opencast mining. The site was then subject to reclamation/backfill prior to first being developed in the late 1800s.
We provided firm advice on the requirements for foundations, including ground gas protection measures and a preliminary slope stability assessment. General contamination levels for a commercial end use were not significant.