Recently, the shield machine on the left line of the third sub-section of Section 4 of the Beijing-Xiong'an Express Line successfully bored through to the intermediate ventilation shaft, laying a solid foundation for the overall breakthrough of the shield-driven section.

Builders celebrate the shield machine's arrival at the intermediate ventilation shaft

The Beijing-Xiong'an Express Line, with a total length of 86 kilometers, connects the Xiong'an New Area and Beijing Daxing International Airport. It is an important component of the Xiong'an New Area's "four vertical and two horizontal" regional rail transit network. Once completed, it will play an important role in relieving Beijing's non-capital functions, building the Beijing-Xiong'an one-hour metropolitan area, and promoting the coordinated development of the Beijing-Tianjin-Hebei region.

Shield segment storage yard

The construction task of the third sub-section of Section 4 of the Beijing-Xiong'an Express Line consists of one shield-driven section and an open-cut intermediate ventilation shaft. The left line of the shield-driven section is 3,605.8 meters long and the right line is 3,550.5 meters long. The intermediate ventilation shaft is 32.4 meters long, 33 meters wide, and 30 meters deep, located within the shield-driven section alignment and used to house equipment such as transformers and ventilators. The section from the launching shaft to the intermediate ventilation shaft on the left line is 2,854.4 meters long. The geology of the shield-driven section mainly consists of silty clay, clayey silt, and fine silty sand strata, and it runs adjacent to the Beijing-Xiong'an Intercity Railway. The construction environment is complex, with high safety risks and great construction difficulty. A shield machine with a diameter of 8.8 meters is used for boring, and this is the only shield-driven section in the Beijing section of the Beijing-Xiong'an Express Line.

Completed shield-driven section

The shield construction area of the project is located south of Daxing Airport. Due to temporary land occupation and the construction plan coordination with the airport, the start of construction was delayed by two years compared with other sections. The builders optimized the construction plan, made every effort to ensure material supply, strengthened control of boring parameters, and enhanced surface settlement monitoring, safely and quickly completing the boring task from the launching shaft to the intermediate ventilation shaft on the left line.

Builders operating the shield machine for boring

During the shield machine's boring to the intermediate ventilation shaft, a 722-meter stretch fell within the 50-meter protection zone of the Beijing-Xiong'an Intercity Railway, with a minimum clear distance of only 21.8 meters. During construction, automated monitoring components needed to be installed within the Beijing-Xiong'an Intercity Railway alignment to monitor data such as line convergence and settlement. To reduce disturbance to the Beijing-Xiong'an Intercity Railway caused by shield boring and to avoid the impact of falling automated monitoring components on train operation safety, the shield machine was required to advance at a limited speed within the protection zone of the Beijing-Xiong'an Intercity Railway.

Acceptance and pre-construction coordination meeting for the test section running parallel to the Beijing-Xiong'an Intercity Railway

Considering the late start of construction, the considerable schedule pressure, and the difficulty of controlling economic risks after speed-limited boring, the builders invited relevant experts for evaluation and demonstration, optimized the monitoring items and methods, and at the same time conducted wind tunnel tests in a professional laboratory to verify the stability of the monitoring components when trains pass at a speed of 250 kilometers per hour. After expert demonstration and optimization, the shield machine was ultimately able to pass without speed restrictions, accumulating valuable experience for similar shield boring in the future.

Shield segment transport

The intermediate ventilation shaft mainly consists of loose soils such as artificial fill, silt, and fine silty sand, with poor stability, high water content, and good permeability. The builders carried out dewatering operations 2 to 3 weeks in advance before foundation pit excavation, lowering the groundwater level of the ventilation shaft to more than 1 meter below the pit bottom to improve the stability of the pit soil and the safety of excavation.

Intermediate ventilation shaft