Abstract:
This paper presents a case study from the Glen Carbon Meijer project in Glen Carbon, Illinois, where drilled displacement piles (DDPs) were used to support a 160,000-square-foot grocery store constructed above abandoned room-and-pillar coal mine workings. The project illustrates the technical and contractual challenges that can arise when specialty foundation systems are procured through design-bid-build delivery but are expected to address poorly defined extreme subsurface risks.
Initial discussions in 2024 focused on conventional foundation support following a saturation grouting program that extended 100 ft beyond the building footprint to mitigate mine subsidence risk. In 2025, the project scope expanded when consultants requested that the foundation system also protect the structure in the event of mine collapse occurring outside the grouted zone. However, no prescriptive subsidence criteria were initially provided, creating uncertainty regarding the performance requirements of the ground improvement system.
A subsidence scenario was eventually established in which collapse outside the grouted limits could produce soil sloughing along a 25° influence angle from the mine horizon, potentially resulting in up to 6 ft of ground displacement at the building edge. Extensive finite-element modeling was performed to evaluate potential soil movements and foundation response. The final design utilized 422 drilled displacement piles bearing in rock to limit building settlement to less than 1 in., while accounting for both clay consolidation and potential downdrag from grade-raise fill.
This paper discusses the iterative modeling process, the challenges of defining realistic subsidence scenarios, and lessons learned regarding risk allocation and performance criteria when designing specialty foundation systems for extreme subsurface events. The case study highlights how delivery structure and incomplete performance specifications can significantly influence foundation design and project outcomes.