Chang Yi Second Line to Xing Lian Road Grand Passage Project (Cross-river Segment)

Project Profile
Name: Chang Yi Second Line to Xing Lian Road Grand Passage Project (Cross-river Segment)
Birth Date: Under Construction / Expected to Open by the End of 2024
Place of Origin: Hunan Province
Length: 5.475 km
Type: Cross-river bridge over the Xiangjiang main navigation channel with main spans of 165+380+165m, semi-floating system with double-tower double-plane cable-stayed bridge, main girder is steel-concrete composite beam
Features: Currently the widest deck, largest single span, and longest cross-river bridge under construction in Changsha (data as of time of publication)
Construction Unit: Changsha Transportation Investment Holding Group Co., Ltd.
Design Unit: Hunan Provincial Communications Planning, Survey & Design Institute Co., Ltd.
Construction Unit: China Communications Construction Company Ltd.
Supervision Unit: Xi’an Fangzhou Engineering Consulting Co., Ltd., Youyi International Engineering Consulting Co., Ltd.

Unique Aspects

The Chang Yi Second Line to Xing Lian Road Grand Passage Project (Cross-river Segment) is located in Changsha City, spanning across the “two districts and one river” of Wangcheng District, Kaifu District, and the Xiangjiang River. It starts from west of Yingxuan Road and ends at the west of the Beijing-Guangzhou Railway Bridge, with a total route length of 5.475 km, including a 4.96 km main bridge across the main navigation channel of the Xiangjiang River designed as a double-plane cable-stayed bridge with double towers and double planes, and a main span of 380m. The approach bridges on both banks are designed with prestressed concrete cast-in-place beams, cast-in-place cantilever beams, steel-concrete composite beams, and steel box girders.

The piers of the main navigation channel bridge adopt a fully buried design, posing great difficulty in underwater cofferdam sinking and positioning; the cable tower design incorporates the regional features of Moon Island, adopting a “Xiang River Elegant Moon” spatial round moon shape with a height of 148.277m, making the ultra-high irregular-shaped cable tower construction technically complex; the main girder adopts a PK-type separated twin-box composite beam form, with a deck width of 38.5m, involving multiple simultaneous operations such as bridge deck and girder lifting, steel girder circumferential welding, cable-stayed cable hanging and tensioning, and UHPC ultra-high performance concrete wet joint construction, resulting in great organizational difficulty; the route spans across the “two districts and one river”, and the approach bridges on land cross urban trunk roads and secondary trunk roads, with numerous road crossings and heavy traffic flow, making traffic diversion for both water and land transportation challenging; the bridge crosses the Xiangjiang River and is in close proximity to residential areas, requiring high standards for civilized construction.

Innovative Aspects

1 Underwater Blasting for Deep Water Bedrock Foundation Pit Formation: The pier foundation location is on bedrock riverbed, consisting of moderately weathered slate rock. The foundation pit excavation was carried out through underwater blasting construction technology, with a blasting depth of 10m in 2 layers. The total blasting volume was about 56,000 cubic meters, making it the largest deep-water blasting project within the Xiangjiang River area. The blasting operation adopted a “underwater drilling + delayed blasting + hole-by-hole initiation” scheme. Debris removal used a “grab dredger + modified 24m long-arm excavator final cleaning” construction method. After preliminary debris removal, an unmanned boat surface scanning technology was used to detect the bedrock elevation and flatness, ensuring the underwater blasting bedrock control accuracy and construction quality, providing favorable conditions for the successful sinking and positioning of the cofferdam.

2 “WMK” Construction Technology for Extra-Large Dumbbell-Shaped Double-Walled Steel Cofferdam: The pier cofferdam innovatively adopted the “WMK” modular assembly construction method, vertically dividing the cofferdam into sections and horizontally into blocks, which were further split into various panel units. These were prefabricated at the factory and assembled in parallel at four sites through unit assembly into blocks, block assembly into sections, and section assembly into the complete structure, enabling multiple processes to proceed simultaneously and in a streamlined manner. Additionally, a new technique of floating and sinking the whole cofferdam with integrated steel pipe clusters was innovatively applied, improving the positioning accuracy and construction efficiency of the steel pipe clusters. The integrated sinking operation also enhanced the strength and stability of the cofferdam during the lifting and lowering process.

3 Deep Water Bedrock Large-Diameter Bored Pile Construction with Reverse Circulation Drilling: For the pier pile foundation, an innovative reverse circulation drilling construction method was adopted. A drilling platform was set up on the completed steel cofferdam to carry out pile foundation construction. During the drilling process, a guide device was used to effectively avoid issues such as drill string twisting, deformation, and low penetration efficiency in hard rock areas. A single pile foundation could be drilled in 4 days, significantly improving drilling efficiency compared to conventional percussive drilling methods. Additionally, the construction process did not require the use of drilling mud, aligning with green and environmentally-friendly construction concepts.

4 Smart Monitoring Technology for Large Volume Concrete Hydration Heat: The pier foundation adopted a dumbbell-shaped foundation base, utilizing the double-walled steel cofferdam as the formwork template. The design concrete volume for a single foundation base reached 7,800 cubic meters, which was poured in two layers vertically to reduce the hydration heat generated by the large concrete volume. To address this, the project implemented internal cooling and external protection water circulation, combined with advanced automatic temperature acquisition technology. Temperature control elements were arranged inside the foundation base, allowing real-time monitoring of the internal and external concrete temperatures via PC and mobile terminals, effectively ensuring the construction quality of the foundation base.

5 Application of Digital and Intelligent Technologies: To address construction processes such as underwater steel trestle bridge installation, double-walled steel cofferdam floating and sinking/positioning, a radar water level and flow velocity integrated instrument was introduced to real-time collect water level and flow velocity data at the bridge location. This allowed management personnel to comprehensively grasp the water conditions of the Xiangjiang River in a timely manner via mobile and computer terminals, ensuring preparedness. An unmanned boat surface scanning technology was adopted for tasks such as collecting underwater blasting bedrock topography data and site detection, replacing the traditional method of using divers for underwater surveying and reducing construction safety risks. A tower crane safety monitoring system was introduced to enable visual monitoring of on-site lifting operations, real-time data collection, and voice alarms, providing effective information support for tower crane construction safety. BIM digital technology was applied for visual briefings on critical processes such as double-walled steel cofferdam fabrication, floating/sinking, and main pier cable tower construction, improving the implementation effectiveness of the proposed plans.