Abandoned Coal Mine Mitigation in Artesian Conditions-Paper

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Glenrock, Wyoming, experienced recurring subsidence, artificial springs, flooded basements, and foundation damage linked to century-old underground coal mines. Groundwater had accumulated in the workings under artesian pressure, creating fractures and pathways through the overlying rock into shallow aquifers.<br /><br />A 2019 pilot study tested whether high-mobility grout could fill mine voids and seal groundwater pathways without causing damage. The team continuously monitored groundwater pressures, controlled water discharge through wells, and used settlement boxes to assess potential ground movement. The pilot showed that grout injection could rapidly raise pressure in the mine, while inadequate discharge could force water unexpectedly to the surface. High-mobility grout penetrated fractures more effectively than lower-mobility mixes, and no notable settlement occurred.<br /><br />Lessons from the pilot informed a 2021 mitigation project covering 14.1 acres in the Oregon Trail Estates neighborhood. A network of monitoring and discharge wells allowed engineers to regulate pressure and flow during injection. The project placed 24,500 cubic yards of grout and released 5.6 million gallons of groundwater in a controlled manner. No construction-related flooding, ground movement, or infrastructure damage was reported. Mine pressure fell by about 3 feet, and shallow groundwater levels decreased by as much as 14 feet; residents also reported persistent improvement in flooding conditions.<br /><br />The project demonstrates that grouting can reduce artesian hazards and subsidence risk in populated areas when supported by thorough site characterization, extensive groundwater monitoring, controlled discharge, close coordination with contractors, and adjustments based on conditions observed during construction.

Keywords

subsidence

artesian pressure

coal mines

groundwater

grouting

mine voids

flooded basements

foundation damage

monitoring wells

mitigation project