A gold mining company had pre-drilled a 380 mm diameter raise bore pilot hole from surface to a depth of 600 m when it was discovered that water-bearing rock fractures were allowing groundwater to enter the pilot hole at a depth of 122 m below surface.
Project engineers requested Peter White to devise a suitable grouting plan and supervise their contractor’s crews to eliminate the water inflow prior to reaming the ventilation raise to full diameter.
Peter designed a diamond drilling layout to intercept the water-bearing fractures from the surface. Completed drill holes were gyro-surveyed so that drill hole locations were established for planning subsequent drill holes.
A large diameter inflatable packer was suspended within the pilot hole below the water-bearing fractures and inflated to allow the pilot hole to fill with water and eliminate water flow down the pilot hole. Filling the pilot hole with water enabled cement grouting of the water-bearing fracture to be accomplished under no-flow conditions.
Water testing and evaluation of drill cores established that aperture size of the water-bearing fractures was relatively narrow, so Peter determined that microfine cement was the appropriate grouting material for this project.
After drilling and grouting of 12 holes surrounding the ultimate ventilation raise diameter, the inflatable packer was recovered from the pilot hole and it was shown that the residual water flow rate from the pilot hole was negligible, allowing reaming of the ventilation raise to proceed.
“Water Cutoff in Raise Bore Pilot Hole” – by Peter White, P.Eng.