The bridge over Lake Volta
Afcons is constructing Ghana’s longest railway bridge over one of the world’s largest man-made reservoirs
The Tema-Mpakadan Railway Project is the largest, and, probably the most ambitious railway project in Ghana. Covering nearly 100kms, the project includes an unprecedented 159 structures. The 300m steel bridge across Lake Volta, which is, at present, underway, is the most critical part of the project. Known for its marine expertise globally, Afcons is pulling off a miracle with the Volta Bridge. Stretching over 8,000 sq kms and more than 70m deep the Volta Lake is one of the largest man-made reservoirs in the world. The bridge is being constructed on the downstream side of the Akosombo Dam over Lake Volta. The width of the lake at the location of the bridge is approximately 300m.
The Volta Bridge consists of five spans of 60m each. It will become the longest railway bridge in Ghana with a superstructure made of 60m steel girder, the longest in the country’s infrastructure history.
“I won’t be exaggerating to say the Volta Lake is bottomless. Driving and boring pile foundations at a depth of more than 70m is an extremely tricky task. This, along with designing the bridge structure at an unpredictable geological location, within time frame, makes the entire activity more complex and challenging,” says Akhil Gupta, Executive Director (Operations), and, Surface Transport BU Head.
Afcons mobilised a special team to design and execute this deep profile bridge. Specialised equipment have been deployed for this critical activity, including a 1,000 MT capacity steel barge (using approximately 350MT structural steel), which was exclusively designed and fabricated in-house with necessary certifications from Volta River Authority and maritime authorities. Reverse Circulation Drill (RCD), Vibro Hammer, 260 MT and 150 MT cranes and tugboats from different countries have been brought in to execute 30 straight and raker piles.
The initial profile of the bridge factored in straight piling. However, following deliberations, raker concrete piles of 1.6m diameter was proposed by Afcons as it would be most conducive as well as cost effective under the existing conditions. The present design provides for vertical piles at abutment locations and raker piles at all pier locations. This is the first-of-its-kind in Afcons’s history, making it another milestone in Extreme Engineering.
However, driving steel liner in the more-than-35m-deep riverbed (at deepest pile location), where the overburden itself is of 35m, led to frequent collapsing. Also, the RCD rig had to be assembled and dismantled several times while driving each pile owing to unforeseen stability and collapsing of overburden.
“Afcons has constructed several railway bridges on water bodies in the past. However, Volta Bridge has been like no other due to the unexpected geological conditions. This special project is challenging the team every moment and teaching us many invaluable lessons,” adds Gupta.
The Volta Bridge is one of the most important infrastructure projects in Ghana. This challenging link of the railway project is set to improve transportation and boost several other projects. The socio-economic impact of the project is massive with a potential to change the face of the region, and, the nation at large. The High Commissioner of India, in Ghana, recently witnessed the laying of raker pile foundation and twitted in appreciation for the innovative construction technology deployed by Afcons.
Watch a short video on Volta Bridge below