A team of engineers and tunnel experts from the Lesotho Highlands Development Authority (LHDA) together with consultants and contractors on the Polihali Transfer Tunnel recently inspected the two TBMs that are being manufactured specifically for the excavation of the 38km transfer tunnel from Polihali to Katse currently under construction.
The Polihali to Katse transfer tunnel is one of main works components of Phase II of the Lesotho Highlands Water Project.
The inspection (factory acceptance test), was conducted by LHDA senior engineers, representatives from Metsi a Senqu Khubelu Consultants (MSKC), the Kopano Ke Matla Joint Venture, which is constructing the tunnel, and the TBM designer, Robbins. The TBM Factory Acceptance Test took place at a CCCC Tianhe plant in Changshu City, Jiangsu Province, China, from 8th – 11th May, 2024.
“We verified the design of the TBMs, their functionality and adherence to safety standards,” said Neo Thinyane, Phase II Senior Projects Engineer. “This included examining the cutterheads, backup systems and segment erection mechanisms.”
The TBMs have been specifically designed to handle the challenging basalt rock formations in the Mokhotlong and Leribe districts where the transfer tunnel is being constructed. The team also assessed the functionality of the muck removal system, conveyor belts, power supply, ventilation, water supply and dewatering systems.
Safety features were a primary focus of the acceptance test. “We checked for adequate walkways, head clearance and body width for workers, gas detection systems for hazardous gases like methane, and the functionality of alert alarms,” Thinyane emphasized. Fire detection and suppression systems were also scrutinized, given the risky nature of tunnel excavation and TBM operations, as were the crucial safe extraction procedures. The TBMs are equipped with refuge bays containing life-support systems, including first-aid kits, oxygen tanks, respirators and air filtration systems. Additionally, there are backup power and cooling systems to ensure uninterrupted operation in case of power outages.
The Polihali Transfer Tunnel will transfer water by gravity from the Polihali reservoir to the Katse reservoir. The excavation will utilize both tunnel boring and drill and blast methods from both ends. The Polihali Transfer Tunnel works include the intake works and gate shaft at the Polihali reservoir, outlet works and gate shaft at the existing Katse reservoir with an underwater connection to the lake, and access adits to the waterway and associated construction infrastructure.
Notable progress has been made on the intake, outlet works, and access adits. The 5.39m diameter TBMs, with 415m backup systems, are expected to arrive in Lesotho later this year.
MSKC designed the tunnel and provided the TBM specifications, while Robbins, designed the machines. Kopano Ke Matla Joint Venture is constructing the tunnel.
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