Mine Shaft Rehabilitation Grouting-Paper

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A 1,928-foot production mine shaft had experienced persistent groundwater inflows, which strained limited storage capacity in abandoned workings and caused deposits on timber sets and guides. Earlier grouting efforts had reduced inflows temporarily, but rates repeatedly climbed back to around 30 US gallons per minute (gpm). Water sampling and investigation identified a connected, approximately horizontal water-bearing feature in carbonate rock near 1,110 feet below ground surface.<br /><br />During a planned shutdown in fall 2020, crews carried out a systematic two-ring grouting program around the shaft. They first injected water-reactive polyurethane resin into inner-ring holes to create a near-shaft seal. Ultrafine cement grout was then used in primary holes in the outer ring. For secondary outer-ring holes, the team selected ultra-low-viscosity acrylic gel to penetrate finer remaining pathways. Additional inner-ring holes were drilled where monitoring showed the polyurethane seal was incomplete. Hole testing and adjustments to grout viscosity and gel time helped direct grout into connected fractures.<br /><br />Before grouting, total shaft inflow measured 31 gpm, including 11.65 gpm from the targeted feature. Shortly after the work, total inflow had fallen to approximately 21 gpm. The feature was well connected around the shaft, with the largest initial inflows concentrated in the northeast, southeast, and southwest areas. The program took about 25 days, close to its 23.5-day schedule allowance.<br /><br />The early results indicate that the 2020 work reduced inflows, but its long-term effectiveness remains uncertain because previous reductions gradually disappeared. The authors identify systematic hole placement, careful drilling, adaptive grout selection, and effective work organization as important contributors to the initial improvement.

Keywords

groundwater inflow

mine shaft

grouting program

polyurethane resin

ultrafine cement grout

acrylic gel

carbonate rock

water-bearing feature

shaft leakage

mine dewatering