Sinkholes — also known as swallow holes or “slugaire” in Irish — are ground depressions or voids formed when surface layers collapse into underground cavities. These features are particularly common in regions underlain by limestone, where the dissolution of calcium carbonate by groundwater can gradually create extensive void networks.
Without a proper ground investigation to depth, sinkholes may go undetected until excavation is already underway — or worse, after construction has begun.
In parts of Waterford, they are often referred to as “falls of ground”, reflecting the frequency of subsurface collapse in karst-prone areas.
During excavation works for the foundation of a one-off dwelling in North Cork, the construction team encountered a significant ground collapse — a sinkhole or swallow hole. Given the potential risk to structural stability, all works were immediately halted pending further investigation.
Substruck Ltd. was engaged to carry out a detailed site investigation and assess the potential for further subsurface hazards. Our scope of work included:
- Desk study: Review of geological, hydrogeological, and historical site data
- Dynamic probing: 12 test points to assess ground strength and variability
- Windowless sampling: To retrieve disturbed samples for classification and analysis
- Factual and interpretative reporting: Delivering both raw data and professional recommendations
The consulting engineer required presumed bearing resistances or allowable bearing pressures at each test location to inform the design of the new foundation system.
Fortunately, no further subsurface anomalies or voids were detected across the site. After applying appropriate torque and blow count corrections, we were able to determine that the ground conditions were suitable for a traditional strip foundation, with adequate bearing capacity at all locations tested.
This case highlights the value of thorough investigation — not only to identify risks but also to confirm when standard construction methods remain viable.
Karst terrains like those found in Cork, Waterford, and other parts of Ireland are particularly susceptible to sinkhole formation. A detailed ground investigation is essential to:
- Identify swallow holes or voided ground
- Assess bearing capacity and soil variability
- Ensure safe and cost-effective foundation design
If you’re planning a development in a limestone area, contact Substruck Ltd. for professional and reliable ground investigation services. Our experienced team delivers the data you need to build with confidence.