At 21:58 on September 22, the right-line shield tunnel of the section from Xingcun Station to Youth Political College Station (all names hereinafter are project names) of Jinan Rail Transit Line 8 was successfully holed through, marking that the entire Phase I project of Line 8 has achieved full tunnel breakthrough, bringing it one step closer to the goal of completion and opening to traffic by the end of 2025.

Phase I of Line 8 starts from Xingcun Station in the west and ends at Qingyuan Street Station in the east, with a total length of 25.5 kilometers, of which the underground section is about 5.6 kilometers. Since the launch of the first shield machine on December 8, 2023, the full holing-through of the underground section has taken only 289 days, 83 days ahead of schedule.

The shield construction of the Phase I project of Line 8 is characterized by "three difficulties and one fast": difficult construction organization due to "four launches from one station"; difficult tunneling due to complex and variable geology; difficult safety control due to crossing multiple risk sources; yet the builders have continuously overcome difficulties, achieving fast construction speed and repeatedly setting new tunneling records.

Difficult construction organization:The shield "four launches from one station" is constrained by objective factors. Of the 5 shield machines on Line 8, 4 were launched from Youth Political College Station. The prefabricated assembly of the station and the shield tunneling construction were carried out simultaneously, resulting in severe cross-operation; 8 "mini trains" about 64 meters long transporting muck and segment linings shuttled within the 230-meter station, very easily causing "traffic jams" and bringing huge challenges to construction organization.

To address these difficulties, the Line 8 project department organized the construction units to scientifically plan the construction sequence, reasonably divide the construction areas, strengthen dynamic control of cross-operations, and assign dedicated personnel to monitor each area, minimizing cross-operation risks to the greatest extent and ensuring the orderly progress of all procedures.

Difficult tunneling process:Complex and variable geology: The geology of the underground section of Line 8 is uneven in hardness and complex and variable, including moderately weathered marl, moderately weathered limestone, strongly weathered marl, crushed stone, loess, silty clay, silt and other geological formations, and there are karst caves. The shield machine traverses "upper soft and lower hard" strata over long distances, which very easily causes abnormal tool wear and affects construction efficiency.

The project team optimized the shield machine selection and cutter configuration according to actual conditions. Following the principle of "frequent inspection and replacement, quick in and quick out," they regularly opened the chamber to check cutter wear, greatly reducing the risk of unplanned downtime. For karst strata, they carried out densified supplementary exploration on the basis of detailed survey, strengthened fine control of complex geology, and adjusted tunneling parameters and grouting parameters in a timely manner to ensure safe and efficient shield tunneling.

Difficult safety control:Crossing multiple risk sources: The underground section of Line 8 is basically located beneath Jingshi East Road, with high requirements for ground settlement and deformation. The shield tunnel in the Xingcun–Youth Political College section passes over the running tunnel of Line 4 and passes beneath multiple risk sources such as Liugong River, Tuhe River, the Zhongtie City pedestrian bridge, and the ramp bridge of Gangxi Interchange, imposing high requirements on tunneling parameter control and shield machine attitude. In particular, where the shield tunnel passes over the Line 4 tunnel, the vertical clear distance is only 2.87 meters, and the Line 4 tunnel has already completed in-tunnel facilities such as track laying, strong and weak current systems, and evacuation platforms.

To ensure absolute safety during construction, the Line 8 project department carefully formulated special construction plans, organized experts to repeatedly demonstrate them, determined the main construction risks and control points, set up trial sections before crossing to define reasonable tunneling parameters, and implemented 24-hour uninterrupted ground and in-tunnel monitoring and patrol during crossing, laying a solid foundation for construction safety.

Fast construction speed:Average monthly tunneling of 230 meters: The construction of Youth Political College Station adopted the green construction technology of prefabricated assembled composite structure, allowing the main structure construction of the station and shield construction to proceed simultaneously, launching the shield 2 months earlier than with traditional station construction techniques. To speed up shield tunneling efficiency, the Line 8 project department firmly grasped project management, formulated detailed construction plans, strengthened assessment and evaluation of project milestones, and promoted efficient and green shield muck disposal technology. Through muck screening and filter-press treatment, they solved the problem of shield tunneling stoppage caused by blocked muck transport.

In addition, by continuously optimizing resource allocation and construction procedures, the construction unit selected management personnel and labor teams with strong professional capabilities and rich construction experience, and set up selection activities such as the over-ring progress award, winning team award, and outstanding employee award. Monthly assessments and evaluations were conducted on safety, quality, progress, and civilized construction, effectively mobilizing personnel enthusiasm. The maximum single-day tunneling reached 36 meters, with an average monthly tunneling of 230 meters, continuously setting new shield tunneling records in moderately weathered limestone strata.