In 2019, DA Smith (formerly Agapito Associates, Inc. Field Services) was commissioned by the North Dakota Public Service Commission—Abandoned Mine Lands Division, Bismarck, to conduct exploratory drilling for the purpose of locating and characterizing historical underground room-and-pillar coal mine entries beneath active commercial properties near Williston. DA Smith completed a total of 54,722 feet of auger drilling with two rigs and two crews over a three-month campaign. Holes ranged from 50 to 110 feet deep and from vertical to 20 degrees off vertical. Over 12,000 feet of 3-inch-diameter casing was installed in holes that intersected voids in preparation for future grouting. Ten holes were core drilled to obtain continuous samples through previously grouted horizons. Ground water samples were collected in select holes. Sites were restored with grading and gravel after drilling.
In 2017-18, DA Smith (formerly Agapito Associates, Inc.) was commissioned by the U.S. Office of Surface Mining & Reclamation & Enforcement, Denver, to drill into and grout abandoned underground room-and-pillar coal mine entries and shafts to abate surface subsidence at five sites in Michigan. The historic mine workings were located approximately 100 feet below surface and actively subsiding at some sites at the time of drilling. Personnel tethers and other special safety equipment were utilized to prevent falling into voids.
Underground voids were grouted with different mixtures of cement, fly ash, sand, aggregates, and calcium chloride. Sinkholes on surface that developed while drilling were backfilled with imported material. Drilling was conducted in both residential neighborhoods and rural fields, requiring coordination with private property owners.
Over a four-month campaign, a total of 10,845 feet were drilled, 6,191 feet of PVC casing installed, and 321 tons of cementitious grout, 1,057 tons of flyash, and 882 tons of sand injected. An additional 486 tons of gravel were placed to fill in sinkholes and other surface depressions. Finished sites were restored upon completion of surface activities.
In 2016, DA Smith (formerly Agapito Associates, Inc. Field Services) drilled 27 holes into the Axial Coal Mine fire located on the Colowyo Coal Mine Lease near Craig, Colorado, for the Colorado Division of Reclamation, Mining and Safety (DRMS). The Axial/Streeter fire burned for more than 70 years prior to drilling activities. A total of 2,925 feet were drilled and approximately half the holes were cased.
DA Smith drilled into the fire using AAI’s track-mounted W/Five drill rig fitted with a HW casing advancer (4½ inch diameter) and down-the-hole (DTH) drilling capabilities. The track-mounted rig (Mooroka chassis) was used because of its ability to tram long distances to the drill site under its own power and work on the rough drill roads cut into the 45° to 65° sloping hillsides (similar to IHI).
Holes were typically 75 to 140 feet long. Foam and water were used to cool the drill bits from the 350°F downhole temperatures. The crew wore special clothing and masks and maintained a gas tester on-site to protect against steam and toxic gases emitted from the fire. The holes were completed with 3.0-inch-diameter black steel pipe, grouted with bentonite grout, and capped. Holes were later used for mine-fire monitoring.