Evaluation of TBM Design for Lesotho Highlands Water Project

This technical report evaluates the design and performance of Tunnel Boring Machines (TBMs) used in the Lesotho Highlands Water Project (LHWP), focusing on Phase 1 and Phase 2 of the project. The LHWP is a multi-phased initiative aimed at providing water to South Africa and generating hydroelectricity for Lesotho. Phase 1, which commenced in 1992, involved the construction of extensive tunnels using Main Beam TBMs in challenging geological conditions. Currently, Phase 2 is under construction, featuring a 38 km transfer tunnel that will utilize both TBMs and drill-and-blast methods. The report details the specifications of the TBMs, including their design adaptations for volcanic rock excavation at significant depths. It compares the modern Double Shield TBMs with the historical Main Beam TBMs, discussing the technological advancements and lessons learned from both phases. The findings aim to inform future tunneling projects in similar geological contexts.