Hejiang is located in the upper reaches of the Yangtze River, and is a developing county. In order to promote its development, the Luzhou-Chongqing Expressway was built to cross the Yangtze River at Hejiang.
The First Hejiang Yangtze River Bridge is 841m long, 4 lanes in two directions, 28m wide and design speed at 120Km/h. It was opened to traffic in October 2017 with cost about 40 million US dollars.
According to navigation requirements, the main span should not be less than 500 m. Engineers compared possible bridge types, they are：concrete cable-stayed bridge, steel truss suspension bridge, steel box arch bridge, and Concrete Filled Steel Tube (CFST) truss arch bridge.
Finally, the owner chose CFST arch bridge with the least material consumption, the lowest cost and the shortest construction period.
The span of this bridge is 530m and main arch reaches a height of 120m. The arch is a truss rib with rectangular arrangement of CFST structure. The width of rib is 4m, the height of arch foot truss is 16m, and the height of arch top is 8m. The empty web tube is arranged by "N" shape. The main girder is composed of steel grid beam and steel-concrete composite deck, connecting arch with suspension cable.
Making full use of the self-erecting capability of steel tube structure, combined with construction conditions, cable hoisting and cable-stayed buckling method were adopted to complete the installation of main arch steel tube.
The arch rib installation segment is 45m long & 16m high. Its lifting weight is more than 200t, lifting height is 140m and the maximum buckle cantilever is 265m, which has high installation risk and difficult construction control.
Traditional manufacturing, transportation and installation segments need temporary components to assist in the formation of structure. As a result, installation weight is heavier, construction period is longer, accuracy is more difficult to guarantee, and construction risk is higher, which can not meet rapid arch-forming needs of 530m CFST truss arch bridge.
Engineers have developed a manufacturing, transportation and installation integrated segment unit, that is, main arch segment unit and cross brace form an independent structural system. No temporary components are needed for manufacturing, transportation and installation. Only in-place matching and welding of main tube needs to be completed at high altitude. All segments in production plant have been manufactured with high precision. Compared with traditional unit, weight is reduced by 30% and welding quantity of high altitude joint is reduced by 33%. One segment was installed in one day only. The installation speed is increased by 2-3 times and the risk and cost are reduced.
The pumping distance of concrete in main arch tube of the bridge is 450m and height difference is 120m. It was necessary for a single tube to be successfully completed 800 m3 C60 concrete pumping once for all and ensure the compactness, which is another technical problem in arching of the bridge.
Two high-performance pumps with pressure greater than 20 MPa are arranged on both sides, and a spare pump can be used at any time to ensure the pressure and the continuity of concrete pumping.
Meanwhile, engineers have proposed pumping technology with high, middle and low three pumping points at half arch, and symmetrical arrangement at both sides, which reduces the difficulty of pumping by 60%. Vacuum equipment is installed on the vault to achieve a negative pressure of 0.8 MPa. By reducing the degassing bag of concrete in main arch main tube, the air content of concrete is reduced by 30%.
Engineers have developed self-compacting pumping concrete with expansibility greater than 600 mm, slump greater than 220 mm, and slump loss less than 30 mm in 12 hours. Meanwhile