The Lesotho Highlands Development Authority (LHDA) has contracted consulting engineering and infrastructure advisory firm Zutari to provide the design and site supervision services for the construction of the Senqu Bridge, the Mabunyaneng Bridge and the Khubelu Bridge as part of the Lesotho Highlands Water Project (LHWP) Phase II.
The company expects to break ground on the project in the second quarter of 2022, with construction timelines of three years for Senqu Bridge and two years for the Mabunyaneng and Khubelu bridges.
The Senqu, Mabunyaneng and Khubelu bridges, which are situated on the A1 national route, the main access road between Oxbow and Mokhokong, are to be reconstructed to higher levels to avoid the flooding of the existing bridges and roads following the impoundment of the Polihali dam.
The Senqu Bridge comprises a 825-m-long, incrementally-launched box girder deck and an extradosed stay cable portion to allow for a 100 m centre span.
“One of the main construction constraints for this bridge is that construction must be completed in time for the impoundment of the dam. The construction time could be reduced by constructing the bridge from both sides. In addition, flooding of the Senqu river might delay construction when a pier is constructed in the centre of the river,” said Zutari transportation services technical director Natie Wilson.
In order to accommodate these two constraints in the design, the normal practice of a temporary steel launching nose was removed and replaced by supporting the front portion of the deck by means of cable stays.
“This pier in the centre of the river was removed, resulting in a 100 m centre span above the Senqu river. This span would be formed by stitching together the two decks launched from either side of the river, meeting in the centre of the 100 m span. The substructure consists of 90-m-high piers founded on spread footings.”
The 120 m Mabunyaneng Bridge and 270 m Khubelu Bridge superstructures consist of variable-depth prefabricated post-tensioned concrete beams, with in-situ cast reinforced concrete top slabs.
The substructures will consist of reinforced concrete wall-type piers and closed-wall abutments with wing walls. The design of these two bridges was carried out by Leporogo Specialist Engineers.
“During construction supervision, Zutari will provide a range of staff, many of whom will relocate to site for the duration of the project. All prevailing Covid-19 regulations will be adhered to and a site-specific health and safety management plan will be compiled by the successful tenderer and reviewed by Zutari prior to commencement of construction,” said Wilson.
Local labour requirements will be coordinated through the LHDA.
“During the tender design stage, skills development was overseen by the Zutari team, with senior staff members working closely with and imparting their knowledge and experience to junior staff members. In addition, two young professionals were seconded by LHDA to Zutari. These individuals were fully integrated into the Zutari design team and hence gained invaluable experience,” Wilson continued.
Key members of the Zutari team are chief design and senior bridge design engineer Johan Kotzé, senior engineering geologist Salona Naidoo, senior road design engineer Francois van Reenen, White Life Consultants environmental specialist Tau Mahlelebe and occupational health and safety specialist Evert de Vries.
“Zutari’s bridge team has a long history of successful bridge designs, including the Siphofaneni River Bridge, a 375 m incrementally launched box girder bridge in 2013 in Eswatini; the Olifants River Bridge, a 166-m-long bridge with a 93 m arch, also in 2013; and the Malibamatso Bridge, a 465-m-long incrementally-launched post-tensioned girder bridge in 1988 in Lesotho,” Wilson added.
As part of a joint venture, Zutari is also involved with the Polihali Diversion Tunnels project and the Polihali Transfer Tunnel project.