AAI drilled and grouted multiple abandoned underground room-and-pillar coal mine entries and shafts as part of a surface subsidence abatement campaign in Michigan for the U.S. Office of Surface Mining & Reclamation & Enforcement, Denver office. AAI completed the grouting with in-house personnel and equipment. AAI subcontracted sonic drilling to Cascade Drilling of Flint, Michigan. A total of 11,000 feet was drilled at five sites.
The historic mine workings were located approximately 100 feet below surface and were actively subsiding at some sites at the time of drilling. Personnel tethers and other special safety equipment were utilized to prevent falling into voids. Subsurface voids were grouted with mixtures of cement, flyash, sand, aggregates, and calcium chloride. Surface sinkholes were backfilled with imported materials. Drilling was conducted in both residential neighborhoods and rural fields, both requiring coordination with private property owners. Finished sites were restored to the owners’ satisfaction upon completion of surface activities. [Contract No. S17PC00010]