The practical completion of the Mabunyaneng and Khubelu bridges on July 31 marked an important milestone in the development of resilient transport infrastructure in Lesotho’s Mokhotlong district.

Constructed by the Concor-Nthane Brothers M&K joint venture (CNBJV) for the Lesotho Highlands Development Authority, the bridges provide permanent access along the national A1 highway, replacing the existing low-level river crossings that will be inundated by the future Polihali dam reservoir.

The contract encompassed the construction of the 270-m-long Khubelu bridge, comprising nine 30 m spans, and the 120-m-long Mabunyaneng bridge, comprising four 30 m spans, as well as two kilometres of A1 Road realignment.

Both structures stand more than 2 100 m above sea level in steep, highly variable mountain terrain.

Delivering infrastructure of this scale in an extreme alpine environment required embedding agility into the project's strategic planning from day one, explained CNBJV contracts director Jaco Verreynne.

“Executing major civil works at this altitude demands complete technical flexibility. By adapting our engineering approach and logistics to match site conditions and severe weather, we have maintained continuous progress while keeping safety at the forefront.”

Early geotechnical site investigations during piling operations revealed that competent founding material lay deeper than originally anticipated.

Engineers promptly adapted the foundation design to incorporate deep friction pulse piles, ensuring structural load transfer through surrounding rock and soil layers.

Further, ground instability along the road approaches led to the original design of the mechanically stabilised earth retaining wall being changed.

Operational execution on site required overcoming significant river-channel and heavy-lifting constraints.

To construct piers within active waterways safely, temporary cofferdams and causeways with culverts were installed to divert river flow without disturbing local ecosystems.

One of the most demanding phases involved the fabrication, transport and installation of the project’s 91 precast concrete beams, each measuring 30 m in length and weighing 51 t.

“Transporting 51 t beams along steep, narrow mountain roads required meticulous logistical planning. Because single-crane manoeuvres were impossible in this terrain, we designed tandem lifting operations using two 275 t truck-mounted cranes in partnership with Johnson Cranes and Jacob’s Transport,” said CNBJV project manager Lebo Matlala.

Specialist partner FB Cranes set up and maintained a dedicated gantry crane system at the on-site Precast Yard to handle precast beam fabrication and loading.

To maintain concrete curing standards during sub-zero winter temperatures, batching water was pre-heated in storage tanks, and enclosed curing environments with industrial space heaters were established around fresh pours.

Further safety innovations included suspending bridge deck formwork directly from the installed precast beams of the bridge structures, drastically reducing high-risk work within active riverbeds.

Environmental controls were integrated across all operations, including dedicated on-site wastewater treatment facilities which treated construction water for reuse in dust suppression, and natural bioremediation techniques that were deployed on site to treat hydrocarbon-impacted soils.

To overcome the 200 km supply distance from commercial suppliers, the JV partnered with National Asphalt to establish a dedicated asphalt plant directly on site.

The project has also delivered substantial economic benefits to the Mokhotlong district.

At peak construction, the workforce comprised about 330 hourly paid workers and 45 supervisory staff, predominantly Basotho nationals. Local procurement significantly exceeded contractual targets across subcontracts for earthworks, security and site services.

Further, the JV provided hands-on training for 12 graduate engineers – 10 from Lesotho and two from Concor’s Graduate Mentorship Programme – building lasting technical capability for the region.

“Infrastructure projects create opportunities that extend far beyond the physical structures. Equipping young engineers and local subcontractors with experience on a mega-project of this complexity builds sustainable capability that benefits the industry long after construction ends,” concluded Matlala.