At the confluence of two rivers and home to a hundred lakes, the great rivers and lakes are a reflection of Wuhan's unique geographical advantages, but also a natural barrier to urban transport development. The Wuchang area contains more than 20 lakes, including Tangxun Lake, China's largest urban lake, and East Lake, the second largest. To solve the problem of poor north-south traffic caused by lakes, Wuhan proposed building a new large underground passage to connect East Lake and Nanhu Lake. Against this backdrop, at the end of June 2020, the long-awaited Two Lakes Tunnel Project officially broke ground.

Rendering of the at-grade section on Zhuodaoquan North Road

The Two Lakes Tunnel runs north from Qinyuan Road to the Third Ring Road, with a Y-shaped main line totaling 19 kilometers. It is built to urban arterial road standards with a design speed of 50 km/h. A 430-meter at-grade section in the middle divides the tunnel into the East Lake and Nanhu Lake sections.

The Nanhu section, designed by CCCC Second Highway Consultants Co., Ltd., starts at East Lake in the north, crosses beneath Nanhu Lake and reaches the Third Ring Road. The 8-kilometer main line includes two underground interchanges and four access points serving travel within the surrounding areas.

Overall technical difficulty ranks among the highest in the world

The shield diameter of the Nanhu section is 15.5 meters, currently the largest in China, making it the longest urban underwater lake tunnel in China and the largest of its kind in the world.

The head of the design team at CCCC Second Highway Consultants said the overall construction conditions for the Two Lakes Tunnel are complex, "no less difficult than building a river-crossing tunnel." Above ground there are lakes, hills, universities, a national 5A scenic area, heritage-protected buildings and many high-rise buildings. Below ground there are areas of strong karst development, full-face hard rock zones and mixed ground with uneven hardness. During shield tunneling, the machine must cross beneath subway lines three times, pass under urban elevated bridges twice and under a railway corridor once. Such conditions are extremely rare for shield tunnels of this scale, and the project's overall technical difficulty ranks among the highest in the world.

The Two Lakes Tunnel adopts a design philosophy of "build without being seen," fully integrating with higher-level planning. Based on the existing road network and greenery, it focuses on restoring and enhancing the roadside landscape, blending it into the environment and hiding the road within the hills and lakes so that it becomes an organic part of the urban environment. Following the principles of adapting to local conditions and ecological conservation, the design retains existing vegetation to the greatest extent possible while ensuring that the improved landscape blends organically with the existing environment of the connecting road sections.

The project starts adjacent to the East Lake 5A scenic area and serves as a passage linking the city and the scenic area. Since this section will be fully reconstructed, and in conjunction with the demolition and redevelopment of Fengguang Village, the design team has applied high standards to this stretch to make it a waterfront landscape avenue that showcases the city's image. A viewing platform overlooking the lake and hills is also designed. The landscape design elements echo the East Lake scenic area and incorporate the historical and cultural elements of Fengguang Village; combined with landscape lighting, this area will become a trendy waterfront nightspot.

Great importance attached to lake protection and water quality improvement

Nanhu Avenue, nestled between hills and water, is scenic and close to Huazhong Agricultural University, making it suitable for slow travel. After the project's ramps are connected, new sidewalks and boardwalks will link the slow-traffic system, and an engaging viewing platform will be designed on the filled flat land at the tunnel ventilation tower, making this a waterfront landscape avenue that showcases the city's image.

The Third Ring Road section has many areas of exposed loess within the red line, and the ecological environment around the interchange is poor. In the project's landscape greening design, large green volume and high coverage are the design principles. Combined with the "sponge city" concept, the terrain will be graded to store rainwater, and aquatic plants and colorful foliage tree belts will be planted along the embankments to create rain gardens and restore the city's "ecological green lung."

Beyond the construction itself, the project also attaches great importance to lake protection and water quality improvement. In response to lake issues of high public concern, it strictly follows Wuhan's lake management regulations to achieve "occupy one, return one" balance, ensuring that after completion the lake capacity and area only increase, never decrease. In addition, the project will build a storage box culvert with a capacity of nearly 50,000 cubic meters beneath the road along East Lake, intercepting outfalls along the route and pumping the water to downstream treatment plants, further improving East Lake's water quality.

On the north shore of Nanhu Lake, in conjunction with the Nanhu Lake water environment improvement project, a row of DN2200 initial rainwater collection pipes will be built along the tunnel structure boundary on Wenhui Street and Zhuodaoquan South Road to intercept initial rainwater from outfalls along the route; once completed, this will significantly purify and improve Nanhu Lake's water quality.

It is reported that once the project is completed, it will create a new north-south underground passage in the Wuchang area, relieving traffic pressure on the eastern section of the Second Ring Road while separating medium- and long-distance through traffic and serving travel within the areas along the route. It is of great significance with outstanding social benefits and will help Wuhan build itself into a national central city.