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HomeAfricaLHWP II’s Senqu Bridge progressing steadily; first deck segment cast on Northern...

LHWP II’s Senqu Bridge progressing steadily; first deck segment cast on Northern abutment

The construction of the Senque Bridge marked a significant milestone on 24 May when the first deck segment was cast on the Northern abutment.

The Senqu Bridge is the largest of the three major bridges under construction to span the Polihali reservoir. Almost a kilometre long (825m) and at a height of 90m, it is the first extradosed bridge in Lesotho. The bridge design has taken into consideration the long, cold and harsh winter conditions experienced in the Mokhotlong highlands. 

Due to the deep valley and the terrain of the area, the deck is being constructed incrementally from both abutments. This will minimize the disturbance to the surrounding work area and increase workers’ safety. An in-situ segment midspan of the centre span will connect the two parts to form a continuous deck. The deck shape is ideal to be constructed with sliding formwork.

The deck segments are reinforced and cast in 25m sections using shutter moulds located in the fixing and casting yard on either abutment. Once cured the section is hydraulically jacked out over the gorge along the tops of the piers and then the process is repeated (see images 1125 and 1139).  The retractable roof seen on the temporary fixing shed will allow more consistent curing temperatures, better working conditions through the long harsh winter as noise abatement for the adjacent community when working night shifts. The first segment has an 8m long temporary noise attached that helps to span between the piers during the incremental launch process.

A significant milestone was reached on 24 May when the first deck segment was cast on the Northern abutment (see image 1148). Visible is the leading cable tube that will house the cables for the 50m long middle section which will be supported by a small cable stay system. This will allow the bridge to span 100m directly over the Senqu River and avoids difficulties of having to build a pier mid-stream on what can sometimes be a ranging torrent.  (Image 1138 is a view from Pier 1 on the Northern bank across to the Southern bank.)

On the southern bank Piers 11 and 14 columns are currently both being constructed simultaneously working 24 hours per day 7 days of the week to complete them in a continuous slide (see image 1153). Overnight temperatures in May in the Lesotho Highlands regularly drop to the lower single figures and only reach the low to mid-twenties during the day. This slows concreted curing time and has reduced the rate at which the piers can be slid from 3.5 – 4.0m a day achieved in summer to 2.0- 2.5m per day currently. The slide of pier 10 in the foreground will be resumed after the completion of piers 11 and 9. (Image 1165 – ‘climbing towards the sky’, the tower crane can be seen delivering concrete to the pier 14 slide team working approximately 10 storeys above the ground.)

Work on the bridge design started in 2018, led by Zutari, formerly Aurecon Lesotho. Zutari also designed the Mabunyaneng and Khubelu bridges, the other two major bridges being constructed under Phase II.

The Lesotho Highlands Development Authority awarded the Senqu Bridge construction contract valued at approximately M2 billion to the WRES Senqu Bridge Joint Venture in August 2022.

The WRES Joint Venture includes South African, Lesotho and international companies as per the requirements of the Phase II Agreement.  The primary partners are:  Webuild S.p.A. (Italy); Raubex Construction (Pty) Ltd (South Africa); Enza Construction (Pty) Ltd (South Africa) and Sigma Construction (Pty) Ltd (Lesotho). Sub-contractors include:  EXR Construction (Pty) Ltd (South Africa; Gleitbau-Geselschaft (Austria); Post Tensioning and Structural Solutions (Pty) Ltd (South Africa) and Freyssinet International et Cie (France).

The Senqu Bridge which is larger that the Mphorosane Bridge on the ‘Malibamats’o River which spans the Katse Dam constructed in Phase I of the Lesotho Highlands Water Project (LHWP), is expected to be completed in early 2026. 

The main water transfer infrastructure works of Phase II of the Lesotho Highlands Water project are the Polihali Dam and the Polihali Transfer Tunnel.

The Polihali Dam will create a 5 042-hectare reservoir at the confluence of the Senqu and Khubelu rivers. It adds 2 325 million cubic metres in storage capacity to the LHWP enabling an incremental increase in the volume of water to be transferred to South Africa from 780 to 1 270 million cubic metres per annum, while simultaneously increasing power generation at ‘Muela by 40 percent.

New roads and bridges are required to restore access across the reservoir and connectivity to the national road network. 

The three major bridges of Phase II are being built along the Maseru to Mokhotlong  A1 road at the Mabunyane, Khubelu and Senqu rivers. They will provide access to Mokhotlong town across the reservoir even at full supply and retain connectivity to the national road network along the A1, the main road between the Mokhotlong district in the mountainous north-east of the country and Maseru, Lesotho’s capital city.

The major bridges programme is complemented by the construction of four pedestrian bridges and six vehicle bridges under the feeder roads and bridges programme to maintain connectivity and ensure mobility for communities in the reservoir area. This programme is currently under procurement.

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