On September 24, the service ramp at Kamoya Project was progressed to K0+926mL at designated ending point, successfully crossed the aquifer.

The breakthrough between service ramp and light-duty ramp is a critical task in phaseⅡ capital construction for the Owner, which also has a great impact to the entire work schedule. The work is designed with a total length of 926m, net profile of 4.2m×4.2m, at -17.5％ gradient, and bolt & mesh support above waist line.The development work was suspended to address large water inflow when progressed to the aquifer (K0+563mL) on November 14, 2019, and then resumed on April 20, 2020 after substantial pumping and grouting were completed (curtain grouting at development ends and grouting behind lining implemented). Although development works were recovered since April, the progress was quite slow as up to 150m³/h water inflow was still encountered for the existence of aquifer.

The biggest uncontrollable risk is power outage, and frequent power failure may result in mine flooding. Under such circumstances, Chinese electricians were on call around the clock to ensure the backup generator could be timely switched on and power failure could be addressed immediately. Meanwhile each water sump is equipped with two pumps and two pipes (1 in operation and 1 for backup) to ensure efficient pumping.

Secondary shotcreting was applied during grouting behind lining to seal the water where leakage happens. In case of large water inflow from bolt holes, φ40 orifice pipes were installed immediately to reduce pressure. Water level at development end was increased by over 30m after each blast and mucking procedure takes up to 12h. Through proactive communication with the Owner, temporary water sumps were established at proper locations to reduce water volume at development end. Shift changes are required to be completed on site for both Chinese and DRC employees to ensure seamless transition between different procedures and to expedite work progress.

The biggest challenge happened during the grouting process at development end. During day shift on July 19, curtain grouting was applied due to large water inflow from cover drilling. However, it was noted that the aquifer was connected to the floor of 3# mucking chamber, which located 30m away from the development end, resulting in mass slurry leakage. Based on previous experience, a 6m long and 0.5m high grouting pad was established inside the chamber with two 6-inch diversion pipes installed at the bottom, but all were in vain. Other measures such as using bigger grouting pad (12m long and 1m high), changing from plain concrete to reinforced concrete, or extending curing days from 3 days to 7 days turned out to be ineffective. Under such circumstances, through various trials such as changing high pressure grouting pump to low pressure grouting pump, reducing water-cement ratio, increasing the volume of water glass, the slurry leakage was finally plugged and sealed during night shift on August 14, post which the development works finally speeded up.

The triumph over aquifer during service ramp development is owing to the solidarity and cooperation of Chinese and DRC employees, strong leadership and support from the Owner and JCHX Overseas Division. The spirit of overcoming difficulties will guide all members through any storms they may encounter in the future.