The entrance to the South African Durban harbor had to be widened and deepened to accommodate ships with very large drafts. However, an existing immersed tube tunnel for water, sewage and electricity ducts was in the way. When planning the new tunnel, it was therefore decided to use mechanized tunnelling as a means of excavation. One of the challenges to be overcome were gradients of 20 percent at both tunnel portals.
The Herrenknecht Mixshield S-327 was customized to meet the challenges of the project. For example, brakes and couplings on the gantry were reinforced. Finally, tunnelling proceeded totally uninterrupted. After four months the target shaft was reached, thereby setting a landmark for mechanized tunnelling in soft ground in South Africa.
