An underground gold mine was rapidly expanding and urgently required additional ventilation capacity to support the operation of its trackless equipment fleet. Ground conditions were exceptionally poor, with exploration drilling results indicating very low RQD values and many zones with no core recovery.
After geotechnical consultants advised that ventilation raises could not be constructed through such adverse ground conditions, the mining company contacted Peter White to ask if the ground improvement was feasible.
Based upon Peter’s experience working in similar ground conditions, the mining company decided to proceed with a cement grouting operation to improve ground conditions prior to raise boring the required ventilation raises.
Peter assembled a turn-key grouting plant, complete with ancillary equipment and accessories for undertaking the planned scope of work, and arranged shipment to the remote mine site in Indonesia.
Ground improvement work involved sequential diamond drilling of 8 holes around the perimeter of each ventilation raise using down-stage methodology. Drilling crews would advance each drill hole stage between 15 to 30 m depending upon ground conditions encountered.
Cement grouting was undertaken using microfine cement to thoroughly penetrate and consolidate fractured ground conditions prior to drilling of the next down stage in each drill hole. Detailed records were maintained of ground conditions encountered, as well as quantity of cement consumed and the applied grouting pressures.
After injecting approximately 40 tonnes of cement along the alignment of each ventilation raise, raise bore crews were able to successfully undertake pilot hole drilling and subsequent reaming to full diameter without difficulty. The excavated ventilation raises remained open without collapse or caving for several weeks until a shotcrete lining was applied.
“Ground Improvement for Vent Raise” – by Peter White, P.Eng.