The Taihu Tunnel on the Suzhou-Wuxi-Changzhou South Expressway, China's longest and widest underwater tunnel, began full-scale construction on the afternoon of January 8. As the largest single-investment project in the history of Jiangsu expressway construction and the most critical node project of the Suzhou-Wuxi-Changzhou South Expressway, this 10.79-kilometer tunnel is not only 1.6 times the length of the Hong Kong-Zhuhai-Macao Bridge immersed tube tunnel but also sets a national record with a net width exceeding 40 meters. The project is scheduled for completion by the end of 2021 and will create a second corridor on the Shanghai-Nanjing route, bypassing the congested Shanghai-Nanjing Expressway and offering new options for travel from Nanjing to southern Jiangsu and Shanghai.

　　Dual six-lane configuration with emergency stopping lanes on both sides

　　The Suzhou-Wuxi-Changzhou South Expressway starts at Qianhuang Town, Wujin District, Changzhou, at the junction of the Nanjing-Changzhou Expressway and the Changzhou-Yixing Expressway, the vertical central axis of Jiangsu. It then runs southeast, intersecting with the Wuxi-Yixing Expressway, passes through Xueyan Town and the Changzhou Taihu Bay Tourist Resort, goes under Yaoxian Mountain into the Mashan area of Wuxi, crosses Meiliang Lake of Taihu, and ends at Nanquan in Wuxi, connecting to the Wuxi Ring Taihu Expressway. The total route length is 43.90 kilometers. The entire line is built to a six-lane expressway standard. The project began with a pilot section in June 2017, with a construction period of four years.

　　According to reports, the total investment is 15.91239 billion yuan, the largest single investment in the history of Jiangsu expressway construction. Compared with the Hong Kong-Zhuhai-Macao Bridge, a "sea bridge-tunnel" project, the Taihu Tunnel is longer and wider. "The Hong Kong-Zhuhai-Macao Bridge tunnel is 6.75 kilometers long, and the Taihu Tunnel is about 1.6 times its length. In addition, the cross-section of the Taihu Tunnel adopts a folded-plate arch two-tube-one-gallery form, with a net width of 40.6 meters, a single traffic tube net width of 17.45 meters, and a net height of 7.25 meters. In addition to the dual six-lane carriageways, both traffic tubes are equipped with emergency stopping lanes, making it 7 meters wider than the Hong Kong-Zhuhai-Macao Bridge immersed tube tunnel, which has no emergency stopping lanes."

　　Preserving the original ecology: 19 years of demonstration before choosing a tunnel over a bridge

　　Should a bridge or a tunnel be built across Taihu? The debate lasted 19 years.

　　A bridge is faster and cheaper; a tunnel costs more but is more environmentally friendly. Ultimately, considering factors such as ecological protection of Taihu, the project chose the underwater tunnel option. Xia Wenjun said that the Taihu Tunnel is located in the Sunan region of the Yangtze River Delta, China's fastest-growing economic area, with abundant tourism resources nearby and crossing multiple environmentally sensitive areas. Environmental factors must also be fully considered during construction to minimize the impact on the ecological environment.

　　Most tunnels use the shield method, such as the familiar Nanjing river crossings, but the Taihu Tunnel uses cut-and-cover construction. Xia Wenjun explained that unlike the Nanjing Yangtze River Tunnel, which is buried 65 meters beneath the Yangtze River, the Taihu Tunnel, although very long and wide, is relatively shallow, with an average water depth of only 1.9 meters. The deepest buried part of the tunnel underwater is only about 4 meters, making cut-and-cover more economical and reasonable, and the shield method cannot achieve the width required for the Taihu Tunnel.

　　How is cut-and-cover done? It is reported that during construction, two rows of steel sheet piles will be driven into Taihu to enclose a cofferdam area, the water inside will be pumped out, and then a concrete tunnel will be cast in the dry area. Construction proceeds from both ends toward the middle, and after the tunnel structure is completed, the steel sheet piles of the cofferdams on both sides will be extracted.

　　According to reports, for such a large underwater tunnel, the amount of excavated soil is staggering. If piled up on an area the size of a football field, it would reach a height of more than 1,400 meters, while the Zifeng Tower is only 450 meters tall.

　　Alleviating congestion: creating another corridor between Shanghai and Nanjing

　　Traffic pressure on the Shanghai-Nanjing Expressway east of Changzhou is increasing, and there is an urgent need for new corridors to divert traffic. According to the Jiangsu provincial highway network plan, the Suzhou-Wuxi-Changzhou South Expressway starts in Changzhou and runs parallel to the Shanghai-Nanjing Expressway, becoming a new southern corridor from Changzhou to Wuxi. Moreover, in the plan, the Suzhou-Wuxi-Changzhou-Nantong Expressway will be extended further east to Suzhou, opening another expressway corridor between Shanghai and Nanjing. At the same time, the project connects northward to the Beijing-Shanghai Expressway and the Wufengshan Bridge on the central axis of Jiangsu, thereby also creating a second high-speed corridor between Beijing and Shanghai.

　　The Suzhou-Wuxi-Changzhou South Expressway is a local expressway established by the National Development and Reform Commission and the Ministry of Transport to support the "three major strategies" and is an important component of the "Horizontal Line 6" in Jiangsu's "five vertical, nine horizontal, five connecting" expressway network plan. Once completed, the project will strongly enhance the functional role of the Shanghai-Nanjing corridor as a major national comprehensive transport corridor, be of great significance to the development of Suzhou, Wuxi, and Changzhou, and become a new engine driving the economic development of the Yangtze River Delta.

　　According to reports, after completion, travelers from Nanjing to southern Jiangsu and Shanghai can go south along the Nanjing-Hangzhou Expressway, turn east onto the S38 Nanjing-Changzhou Expressway, reach southern Changzhou, and then take the Suzhou-Wuxi-Changzhou South Expressway to Wuxi, Suzhou, or Shanghai.