Abandoned Coal Mine Mitigation in Artesian Conditions-PPT Presentation

PPT Presentation

Pdf Summary

The presentation describes mitigation of abandoned coal mines beneath Glenrock, Wyoming, where more than 855,000 tons of coal were mined before operations ended in 1909. The flooded workings have created artesian conditions, with roughly 112 years of accumulated water and a reported pressure head of 175 feet. Risks include subsidence, groundwater entering homes and infrastructure, and pressure changes caused by grouting or dewatering.<br /><br />A 2019 pilot tested whether mine voids could be grouted safely beneath a developed neighborhood. The program used monitoring wells, settlement load cells, a groundwater-discharge well, and approximately 4,975 cubic yards of grout across 1.9 acres. No measured load-cell movement exceeded 1–2 millimeters, indicating that mitigation could be carried out without significant settlement or heave. The pilot also showed the importance of monitoring shallow and deep groundwater and providing a means to release mine-water pressure during grouting.<br /><br />The larger Oregon Trail Estates project began in 2021, covering 14 acres with 598 boreholes averaging 150 feet deep. Crews injected about 24,538 cubic yards of grout into mine voids and rubble. Six permitted wells on the site’s northwestern edge intercepted and discharged mine water; monitoring wells tracked groundwater response. Water levels changed soon after work began, and shallow groundwater levels declined substantially and remained lower during the project.<br /><br />The approach prioritized filling mine voids, joints, fractures, and rubble rather than maximizing grout strength. The presentation concludes that mitigation under artesian conditions is feasible, but requires careful pressure management, groundwater monitoring, and coordination of grout injection with controlled water discharge.

Keywords

abandoned coal mines

Glenrock Wyoming

artesian conditions

subsidence mitigation

grouting

groundwater monitoring

mine voids

dewatering

Oregon Trail Estates project

pressure management