At 3:45 a.m. on June 13, the Xianyang Caihong 2nd Road Viaduct—the double-cable-plane prestressed concrete cable-stayed bridge with the largest single-unit tonnage in China built using the two-stage horizontal rotation method, surveyed and designed by China Railway First Survey and Design Institute Group and constructed by China Railway 17th Bureau Group—completed its clockwise 93-degree rotation in 105 minutes, laying a solid foundation for the early opening and operation of the line.

Full view of the bridge after rotation

The Xianyang Caihong 2nd Road Viaduct starts from Yuquan West Road in the north and ends at Baoquan Road in the south, with a total length of 885 meters. It crosses 9 railway tracks including the Xuzhou-Lanzhou High-Speed Railway and the Longhai Railway, connecting the north and south urban areas of Xianyang. Once completed and opened to traffic, it will further improve the urban three-dimensional traffic road network and inject new vitality into building the Xianyang core area of the "Greater Xi'an" metropolitan circle.

The main tower of the rotating portion of the bridge is an A-shaped bridge tower, 84.778 meters high, and the girder body is 221 meters long, with a total weight of about 50,000 tons, equivalent to the weight of 10,000 adult elephants weighing 5 tons each. Because the work site is close to the railway line, with a train passing every 4 minutes on average, and because the twin-tube tunnel of Xi'an Metro Line 1 runs through the pile foundation group of the rotation pile cap, how to "calmly turn" a massive structure weighing tens of thousands of tons while ensuring the safe operation of the existing line became a major challenge for the builders.

Handling a heavy load with ease, skillfully using "embroidery-level precision"

Employee Innovation Studio (Photo by Pu Yihui)

To reduce the impact of construction on the existing line, China Railway First Survey and Design Institute Group and China Railway 17th Bureau Group, together with industry experts, conducted multiple scheme demonstrations and ultimately determined to adopt the two-stage rotation construction method of "single-tower rotation + tower-girder joint rotation," rotating the main tower and then the "main tower + girder body" in sequence. This successfully solved many problems such as the large rotation weight of the bridge, the rotation foundation spanning the subway, the main bridge construction being close to the existing line, and the narrow construction space.

To handle a heavy load with ease, one must first treat a light load as heavy. The key to the bridge's "magnificent turn" lies in the core components of the rotation system. The project team adopted a domestically super-large-diameter pot-type rotation force-measuring bearing with independent intellectual property rights, with a diameter of 7.78 meters, a total weight of about 150 tons, and a designed bearing capacity of 80,000 tons, effectively solving the problem of concentrated stress during the rotation of a large-tonnage rotating bridge. It smoothly completed the clockwise 93-degree rotation construction, setting a new record for similar construction in China.

Challenging the limits, empowering quality construction

Schematic diagram of the relationship between bridge pile foundations and the subway (Photo by Pu Yihui)

Within the 105-minute window, the 50,000-ton "main tower + girder body" had to be rotated clockwise by 93 degrees. Facing challenges such as the large tonnage and high center of gravity of the rotating structure, the project team relied on the smart construction site management platform to establish a real-time monitoring system for "tower-girder joint rotation," comprehensively applied BIM, 3D visualization disclosure, and other means to carry out detailed design, and conducted pre-simulation analysis of complex structure quantity verification, rebar and pipeline collision checks, and spatial component coordinate calibration, accurately mastering the extreme working conditions of rotation construction and ensuring that each process was completed in one step and achieved excellence at the first attempt.

In addition, the project established an innovation studio to carry out special research on key technologies for refined construction control of "tower-girder joint rotation." During the rotation process, advanced equipment such as automatic aiming technology and high-definition video macro monitoring were comprehensively used to ensure that construction precision was controlled at the millimeter level. When the bridge body was 1 degree away from the designed rotation angle, the rotation power system switched to jog mode for fine adjustment to ensure precise positioning of the bridge body. The series of key control technologies summarized and formed by the project filled gaps in relevant research fields in the industry. 

Wind passes without a trace, building a solid safety defense line

Bridge structure monitoring system (Photo by Pu Yihui)

The twin-tube tunnel of Xi'an Metro Line 1 runs through the pile foundation group of the rotation pile cap. The space between the shield tunneling section and the pile foundation is narrow, with a minimum distance of only 1 meter. Considering the large transverse span of the rotation base turntable, the project team strengthened geological exploration, established a monitoring system, and coordinated measures such as a three-directional prestressing system to conduct data analysis, ensuring that the stiffness of the upper structure of the bearing turntable met the bearing capacity requirements of "two-stage rotation" while also taking into account the impact of surface settlement, providing experience for the construction of large-span bridge rotation systems in complex urban environments at home and abroad.

Because the main girder of the bridge is only 4.05 meters away from the railway line at its closest point, construction control requirements are extremely high. The project team adopted an electronic radar intrusion prevention system, forming a spatial electronic curtain wall through scanning laser radar to monitor and alarm large equipment that crosses the boundary and intrudes into the limit. Together with measures such as dynamically optimizing process organization and grid-based dedicated personnel key monitoring, it comprehensively safeguarded the smooth "turn" of the cable-stayed bridge with the largest single-unit tonnage in China.