Drill and blast achieves Lesotho double breakthrough

23 August 2021

Double breakthrough and substantial completion has been achieved on the nearly 1km-long Polihali diversion tunnels of the Lesotho Highlands Water Project Phase 2.

The nearly 1km-long tunnels – of diameter 9m and 7m – run roughly parallel to each other. Excavation of both began in June 2020 and has advanced at a rate of around 5m/day per tunnel. Drill and blast was used for excavation, with sprayed concrete, rock bolts and mesh used for support. Work is continuing on the concrete intake structure for the 7m-diameter tunnel, while that for the 9m-diameter tunnel is almost complete. Erosion control and flood protection work was completed previously.

The tunnels will divert the Senqu River to create a dry foundation and work area for the construction of the Polihali Dam, for which the Lesotho Highlands Development Authority launched the tender on 5 August 2021.

Tunnel engineering design and consultancy has been provided by Metsi a Senqu-Khubelu Consultants Joint Venture (MSKC) and the contractor was the SCLC Joint Venture comprising the Webuild, CMC di Ravenna, Lesotho-based LSP Construction and CMI Infrastructure.

Overall completion of the tunnels is planned for the end of 2021.