Interconnecting Tunnel from Mohale to Katse
This 4,5m diameter, 32km long tunnel will link the
two major Phase 1 reservoirs, allowing water to flow in either direction, and keeping each dam at optimum operating level. It is expected to be transferring water in 2003.
The intake to the tunnel is submerged So that the environment is not disturbed by additional structures. Many of the lessons learnt in the construction of the Phase lA Transfer Tunnel are being applied here, as the tunnel goes through similar basalt rock. Two shielded TBM's are being used for excavation, while the tunnel is fully lined with hexagonal, four- piece pre-cast Concrete segments, cast on-site. There are no bolts or seals in this type of lining, and it is one of the faster methods of lining a tunnel.
Commissioning the two shielded TBM's proved to be a challenge in the beginning, but once the crew mastered the sophisticated machines, progress was significant. However, both crews are experiencing large water features (underground water) that require pumping and grouting before boring can resume. The revised programme for the two machines means that the Katse outlet machine will bore slightly more than the Mohale inlet machine. The tunnel engineers are confident that they can still have the tunnel ready by 1 January 2003, the contractual date set for the first transfer of water.
