Recently, the south anchorage of the north channel bridge of the Zhangjinggao Yangtze River Bridge completed the 1,481st pile of deep foundation reinforcement. 60% of the total reinforcement has been completed. The deep foundation reinforcement is the first of its kind in the industry and is a brand-new anchorage construction technique.

High difficulty: inserting "chopsticks" into a "tofu block"

The south anchorage of the north channel bridge of the Zhangjinggao Yangtze River Bridge is located on Jiangxinzhou, where the soft overburden layer of the foundation is thick, and there is no bearing stratum or natural aquiclude that meets the design requirements of the bridge foundation structure. The design pioneered the use of a large-area ultra-deep foundation reinforcement scheme for foundation reinforcement and improvement. The reinforcement area is about 6,000 m², equivalent to the size of 15 standard basketball courts, with a total of 2,497 concentric variable-diameter piles and a maximum reinforcement depth of 52.8 m. With large areas, great depths, and undulating geological conditions, how to ensure stable and reliable construction quality for the 2,497 reinforcement piles—the quality of each pile is crucial. To this end, the CCCC Road & Bridge project team launched a technical assault on the first pile.

Eight months of hard work, over a thousand tests

To obtain a stable set of construction techniques and a set of construction parameters that ensure project quality, the project team began testing. The area where the south anchorage is located was formed by river sand deposition. The difficulty of building a world-class bridge project on soft foundation like a tofu block is self-evident. The project team innovatively adopted large-area deep foundation reinforcement technology, like inserting 2,497 pile foundations into a tofu block to firmly support an anchorage weighing about 500,000 tons. Not only that, the foundation must also meet water-blocking requirements to ensure that the anchorage foundation pit excavation does not leak. Although the island lacks water and electricity, a test team of more than 40 people carried out round after round of testing. From winter to spring, the test results were still unsatisfactory. The project team found that existing construction techniques were all difficult to meet the pile diameter requirements. Only the RJP technique had relatively slightly better test results and was more economical. "If the two cutting passes are not effective, can we cut the pile diameter to the required size in one pass by increasing the upper cutting water pressure? The lower nozzle is only used for grouting. In this way, can we avoid the difficulty of the RJP technique in meeting the pile diameter requirements?" A reverse idea brightened everyone's eyes. Tests proved that this approach was indeed effective. After multiple parameter adjustments and core sampling comparisons, the project team spent 8 months and started over countless times, finally finding the "password" to unlock the 2,497 pile foundations. The project team improved the existing technique with 650 mm large-diameter pilot holes, enabling the verticality of the pilot holes to reach L/600, more than 3 times higher than the original technique, effectively ensuring the verticality of pile foundation construction; optimized process parameters and innovatively proposed the D-RJP construction method, combined with the re-grouting technique, to ensure pile diameter while effectively improving the strength and stability of the pile body. The project team completed 60% of the deep foundation reinforcement in only 5 months.

Upholding integrity and innovating, improving quality and efficiency, and building the brand

"Micro-innovation" solves "bottleneck" problems, and digital empowerment provides solid data support for project construction. The project team innovatively developed an intelligent construction system, creating functional modules covering 3D scene twinning, integrated control center, equipment and material twinning, schedule management, quality management, green and low-carbon management, and test and inspection management. Through full-factor data collection and transmission and the storage and management of multi-source heterogeneous data, the "digital twin" model drives the intelligent construction system, enabling intelligent control and forward and reverse traceability of the deep foundation reinforcement construction process, helping to make hidden engineering quality management refined, information-based, and intelligent, and striving to build a national-level smart construction site demonstration project.