Drilled Displacement Piles to Mitigate Potential Mine Subsidence: A Case Study in Performance Definition Under Design-Bid-Build Delivery-PPT Presentation

PPT Presentation

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The presentation describes a 160,000-square-foot Meijer store built over an abandoned room-and-pillar coal mine in Glen Carbon, Illinois. The site had deep soft clays over shale, with the mine roughly 200 feet below grade. A mine-grouting program treated the area beneath and around the building, but residual risk remained beyond the treatment limits.<br /><br />The main challenge was defining the building’s required performance before specialty foundation design began. Stakeholders initially disagreed over whether ground improvement should simply support building loads or protect the structure against potential mine-related subsidence. The final design scenario assumed collapse outside the grouted zone, soil sloughing at a 25-degree angle, and five inches of displacement at the building edge. The performance target was to limit total building settlement to one inch and protect columns and walls; saving the slab was not required. Responsibility for lateral movement also needed clarification.<br /><br />After evaluating alternatives, the project used 422 Continuous Flight Auger (CMC) rigid inclusions extending to rock at about 80 feet. Footings bore directly on the inclusions, which were upsized to account for downdrag from fill. Reinforcing cages provided additional protection against lateral movement. Installation took just over five weeks, with cage installation difficulties and equipment and weather delays.<br /><br />The project required iterative numerical modelling to represent the prescribed extreme-event settlement, highlighting that such analyses depend heavily on assumed collapse mechanisms. The authors’ key lessons are to establish extreme-event criteria and risk ownership early, coordinate lateral-resistance responsibilities, and ensure stakeholders agree on what the foundation system must protect against. Statistical confidence in mine stabilization alone does not define acceptable structural performance.

Keywords

Meijer store

coal mine

mine grouting

ground improvement

rigid inclusions

continuous flight auger

settlement criteria

foundation design

subsidence risk

numerical modeling