How was the under water tunnel built in Shanghai?

Shanghai’s Bund Sightseeing Tunnel is the first immersed tube tunnel ever built in China, and the largest immersed tunnel project in general, with a total length of 890 meters (2,919 ft). Its construction period lasted from Oct 2007 to Apr 2010, and it began full operation in July 2010.

Immersion method, or immersed tunnel, is an approach to building tunnels using prefabricated tunnel elements that are sunk onto the river or seabed. Immersed tunnel methodology ensures fast construction, reduced disturbance to the environment and river traffic, and is usually considered to be of relatively low cost.

Construction process:

1. Construction of the Tunnel Elements: The tunnel elements, also known as segments, were prefabricated in a dockyard located in Taicang, Jiangsu Province. Each segment was made of reinforced concrete and had a length of 16.5 meters, a width of 33 meters, and a height of 10 meters.

2. Dredging and Foundation Preparation: The section of the riverbed where the tunnel was to be placed underwent dredging to achieve the required depth and shape. A layer of sand and gravel was then laid down as a foundation layer to provide support for the segments.

3. Segment Transportation: The prefabricated segments were transported from the dockyard to the construction site by using heavy-lift barges.

4. Segment Lowering and Alignment: To sink the segments into place, a process known as segment lowering, a series of submerging vessels were used. These vessels were equipped with powerful winches and controlled the descent of the segments into the pre-prepared trench on the riverbed. Advanced GPS systems and sonar equipment ensured that the segments were positioned accurately.

5. Segment Connection and Sealing: After one segment was lowered and settled into its position, it was connected to the previously placed segment using temporary bolts. Divers would inspect and verify that the segments were correctly aligned and sealed. Watertight gaskets and epoxy injections were used to create watertight connections between segments.

6. Backfilling: Once all segments were in place, the empty spaces between the tunnel elements were filled with a mixture of sand and gravel to lock the tunnel elements in place and to protect the tunnel from external factors.

7. Interior and Finishing: After the tunnel structure was completed, the interiors were fitted out with electrical and mechanical equipment, ventilation systems, drainage, lighting, and emergency systems. Final construction works, such as road surfacing, and safety markings, were also completed.

Opening for Traffic: The Shanghai Bund Sightseeing Tunnel was officially opened to the public in July 2010, serving as a major transportation artery beneath the Huangpu River, enabling vehicles and pedestrians to conveniently travel between the Bund and Pudong areas of Shanghai.