As the first large-scale control project on the main canal of the South-to-North Water Diversion Central Route, the Tuanhe Aqueduct is currently the world's largest "U"-shaped aqueduct. Renowned for its highly ornamental value, it is also hailed as the "First Span of the Thousand-Li Main Canal."
　　The clear water of the Danjiangkou Reservoir travels all the way north, and after a long journey, flows into ordinary households. During this process, the greatest challenge is conquering the numerous technical difficulties in the project. As the main works of the Henan section of the South-to-North Water Diversion Central Route Project are fully connected and the water delivery date approaches, reporters visited the project site to see how construction workers overcame one world-class challenge after another to ensure that the water from the south reaches Tianjin.
　　Five Years to Overcome a World-Class Challenge
　　The South-to-North Water Diversion Central Route Project starts from the Taocha Canal Head in Xichuan County, Henan Province, and proceeds northward, but the presence of expansive soil has slowed the pace of the water's advance. From the canal head to Tianjin, the main route of the central line, with a total length of more than 1,000 kilometers, has nearly 400 kilometers of canal that must cross expansive soil areas. Expansive soil is a worldwide technical challenge. When building canals on expansive soil, this type of soil repeatedly swells when it absorbs water and shrinks when it loses water, causing canal collapse. To overcome this difficulty, the expert panel conducted more than 10 years of research, with field tests alone lasting as long as 5 years. It was not until August 2011 that the construction plan was finally determined—replacing the expansive soil with cement-modified soil, adding cement to the expansive soil to change its property of "swelling when wet and shrinking when dry."
　　October Water Delivery Enters the "Countdown"
　　The water from the south continues its journey and passes through Fangcheng County. Located in the southwestern part of Henan Province, Fangcheng County is the "northern gateway" of the Nanyang Basin. The Fangcheng section is the area with the most complex geological conditions along the entire central route, and it is also where the Section 6 project of the Fangcheng segment is located. The canal in Section 6 of the Fangcheng segment has a total length of 7.55 kilometers and 10 cross-canal structures, including 3 inverted siphon projects. At the site, reporters saw that the Baihe inverted siphon project adopts a design with pipes buried beneath the riverbed and two pipes connected in one unit, with a total of 4 pipe culverts; within a single culvert opening, two large trucks can easily pass side by side. It is understood that the inverted siphon project is a relatively large control project in the South-to-North Water Diversion Central Route Project. The project uses the pressure of the water flow in the canal itself to enter the riverbed from the inlet and then emerge from the outlet, thereby ensuring the normal water conveyance, irrigation, and flood discharge requirements of the river while also ensuring water quality. At present, the main works have been completed and can basically guarantee the requirements for water delivery in October.