Tunnel boring by a tunnel boring machine (TBM) has started in the highlands of Lesotho, marking the first time this has occurred since tunnel construction under Phase 1 of the Lesotho Highlands Water Project (LHWP) began more than 20 years ago.

The Katse TBM, the first of two double-shielded TBMs designed to excavate the 38 km Polihali transfer tunnel, in Lesotho, will dig about 20 m underground a day from the Leribe side, with concrete segment tunnel lining installed as excavation progresses.

The second TBM, which will dig the tunnel from the Polihali side, is expected to arrive on site by the middle of the year.

The new milestone of Khoiti ea Ngoaha Kholo2, the name given to the TBM by Lesotho Prime Minister Samuel Matekane in line with the tradition of naming TBMs prior to boring activities, represents a significant advance in the construction of Phase II of the LHWP.

According to a media statement sent to Engineering News & Mining Weekly by the Lesotho Highlands Development Authority the traditional TBM naming followed a national TBM naming competition, where Mary Taolana suggested the name Khoiti ea Ngoaha Kholo2, which means ‘the rat mole of 200 years’ and was confirmed through public voting by Basotho.

The TBMs, designed by US-based tunnelling technology firm Robbins, were manufactured by CCCC Tianhe of China, at a plant in Changshu City, specifically for the excavation of the Polihali–Katse transfer tunnel.

“This milestone reflects the dedication and commitment of the government of Lesotho, the Lesotho Highlands Water Commission, the LHDA, and all consultants and contractors involved. I am confident that with the continued partnership and support of the government of the Republic of South Africa, we will achieve great things for both our nations,” Matekane said.

The 423-m-long TBM machine, with the cutter head diameter at 5.38 m, left China on July 20 and arrived, after four weeks at sea, at Maydon Wharf in Durban on August 26.

The components, including cutterheads, backup systems and segment erection mechanisms and gas detection systems for hazardous gases like methane, alert alarms, fire detection and suppression systems, were transported by abnormal load vehicles from Durban to Lesotho, arrived at the Caledonspoort/Butha Buthe border post on September 4.

Lesotho transport and logistics company Orange Primate Logistics was engaged to transport the 126 pieces of the TBM.

The TBMs are also equipped with refuge bays containing life-support systems, including first-aid kits, oxygen tanks, respirators and air filtration systems, as well as backup power and cooling systems to ensure uninterrupted operation in case of power outages.

The 38-km-long, nominal-bore 5-m- diameter Polihali–Katse transfer tunnel is a key component of Phase II of the LHWP to transfer water from the Polihali reservoir to the Katse reservoir.

It will facilitate the gravity transfer of water from the Polihali reservoir to the Katse reservoir, enabling the transfer of 1 270 m3 of water, thereby towards meeting the increasing water needs of South Africa’s Gauteng province.