At 2:39 a.m. on July 26, as the last batch of concrete was poured into the borehole of Pile No. 60 of Pier 4 of the main bridge, the pile foundation works for Pier 4 of the Chizhou Yangtze River Highway-Railway Bridge undertaken by Xuteng Foundation were successfully completed 100 days ahead of schedule, laying a solid foundation for the subsequent construction of the bridge.

The Chizhou Yangtze River Highway-Railway Bridge connects Guichi District of Chizhou City and Zongyang County of Tongling City, with a total length of 3.1 kilometers, of which the main bridge is 1,768 meters long. It is a three-main-truss, three-cable-plane double-deck steel truss cable-stayed bridge with a span arrangement of (100+378+812+364+114) meters. The south cable tower of the bridge is 274.5 meters high and the north cable tower is 282.5 meters high; both are elegantly shaped spatial diamond-type reinforced concrete bridge towers, earning it the reputation of the "Bridge in the Sky."

Rendering

The Chizhou Yangtze River Highway-Railway Bridge features long spans, heavy loads and high speed, and is built to the standard of a combined river crossing for "highway + intercity railway + urban rail transit." The upper deck serves as the river crossing channel of the Ningzong Expressway, arranged with six lanes in both directions and a design speed of 100 km/h; the lower deck carries the two-track Hechi Intercity Railway with a design speed of 250 km/h, and reserves two tracks for the Chitong Regional Railway with a design speed of 160 km/h. It is the sixth highway-railway bridge across the Yangtze River in Anhui Province.

Bridge Type Layout of the Chizhou Highway-Railway Bridge

Xuteng Foundation was mainly responsible for the pile foundation works of Pier 4 of the main bridge and Pier 5 of the auxiliary pier, both of which have been successfully completed. Pier 4 of the main bridge consists of 77 bored piles with a diameter of 2.8 meters, a pile length of 112 meters, a borehole depth of 138.5 meters and an average rock-socketed depth of 105 meters; Pier 5 of the auxiliary pier consists of 12 bored piles with a diameter varying from φ2.5 meters to φ1.8 meters, an average borehole depth of 106 meters and a pile length of 100 meters. The special geological and hydrological conditions and the construction characteristics of ultra-long and ultra-deep bored piles posed certain difficulties for such operations as borehole verticality, fabrication, splicing and lowering of reinforcement cages, underwater concrete pouring and ultrasonic testing of foundation piles. In addition, with multiple pieces of equipment operating simultaneously and a narrow working area, safety became the top priority. To ensure the smooth completion of the pile foundation, under the scientific organization and meticulous deployment of China Railway Major Bridge Engineering Group Co., Ltd., Xuteng Foundation clarified the processes, optimized the schemes and refined responsibilities on site, achieving all-round control over production, quality and safety. The step-by-step hole enlargement drilling technique was adopted, with 2 XR800HD rotary drilling rigs, 1 XR700E rotary drilling rig, 1 XR600E rotary drilling rig and 4 XR580HD rotary drilling rigs put into use. A self-developed slurry preparation system was used to mix and pump slurry, producing high-standard mud to ensure its suspension capacity and stability and to maintain borehole wall stability during drilling. To address the hole enlargement caused by geological conditions during drilling, the following measures were taken: when opening the hole, bentonite was added inside the casing and mixed with a slurry-mixing drill bit to prepare thick slurry with a higher specific gravity than normal mud for starting the new hole, and after drilling into the rock stratum, normal mud was used for drilling, so as to form a relatively stable wall protection in strata prone to severe hole enlargement.

As Pier 4 of the main bridge is a pier in the river, the project department attached great importance to environmental protection during the construction of the bored piles of the main pier. To prevent mud from polluting the Yangtze River, the project department used two mud boats, on which slurry mixing was carried out exclusively, and the slurry was delivered to each steel casing through sealed pipelines. During the construction of the bored piles, the project department set up drill cuttings boxes at each borehole on the working platform and transported the cuttings to the spoil ground by dump trucks with enclosed cargo compartments, eliminating the risk of river water pollution caused by mud leakage. In addition, through the adoption of innovative technologies, the project department installed a sewage collection-filtration-purification system on the trestle bridge, so that the sewage from routine washing of the trestle deck was uniformly delivered through the sewage collection pipelines laid along the edge of the platform to the sewage purification equipment, and discharged after purification treatment, making every effort to reduce possible pollution caused by construction. 

The technical director of the Xuteng R&D Center led the team throughout the process

Construction of Pier 4 of the main bridge

XR800HD rotary drilling rig with a maximum drilling diameter of 4.6 meters and a maximum drilling depth of 160 meters

Installation of reinforcement cage

Primary and secondary cleaning using combined air-lift reverse circulation cleaning equipment

Pouring by the pouring frame ball-pulling method

Pile integrity testing

After the Hefei-Chizhou Intercity Railway and the Chizhou Yangtze River Highway-Railway Bridge are completed and put into operation, they will open up highway and intercity railway transportation corridors from Hefei via Chizhou to southern Anhui. Passengers can travel directly by EMU trains between Hefei and Chizhou without detouring through Tongling, Anqing and other places, which is of great significance for further strengthening infrastructure construction in the Wanjiang region, improving the layout of river crossing channels and advancing the implementation of the Yangtze River Delta integration development strategy.