30 Three water tunnels in Natal, South Africa

Three tunnels have been constructed, in Natal, as part of a scheme to augment the water supply to the Greater Durban area. The tunnels have been excavated in sandstones, tillites and shales using drill and blast and a full face tunnel boring machine. The paper describes the interesting aspects of the respective driving methods and their relative performance. The use of a tunnel boring machine on one section of the tunnels enabled this pressure tunnel to be redesigned using a waterproof membrane and installation of this waterproof membrane is described.

• THE UMGENI LOW LEVEL SCHEME

• GEOLOGICAL INVESTIGATIONS

• TUNNEL BORING MACHINE

• PROGRESS RATES

• PRIMARY SUPPORT

• TUNNEL PROFILE

• SECONDARY LINING DESIGN

• SECONDARY LINING INSTALLATION

• CONCLUSIONS

• REFERENCES