At around 11 a.m. on March 6, with a loud "bang," the connecting-line tunnel of the access line section of Phase III of Shenzhen Metro Line 8 — invested in and built by Shenzhen Metro Group, general-contracted by China Railway Southern, and constructed by China Railway First Group — was successfully holed through, achieving a victorious breakthrough to meet the three-line large-section tunnel. This marks a new phase of "vigorous and rapid construction" for the mined tunnel of the access line section, and is another important milestone since the transition to large-section tunnel construction, laying a solid foundation for the completion and opening of the entire line.
The Phase III, Section 2 project of Shenzhen Metro Line 8 is located in Dapeng New District and includes one station and one access line. The construction methods for the access line are the open-cut method, shield method, and mining method. Among these, the starting empty-push section, TBM section, mining-method mined section, and terminal open-cut section are constructed by the Urban Rail Company of China Railway First Group.
The connecting-line tunnel holed through this time is 348 meters long, with a span of 6.9 meters and a height of 7.5 meters, in a horseshoe shape, with an excavation area of 42 square meters, and is constructed by the drill-and-blast method. The tunnel passes through complex strata, transitioning from Grade V surrounding rock at the initial portal to Grade II surrounding rock, and crosses fractured zones multiple times. Smooth blasting is highly demanding, the technical difficulty is great, and safety risk control is challenging. The tunnel passes close alongside Kengweitou Reservoir and a 400 kV power tower, involving difficult permit procedures, numerous controlling factors, high environmental protection requirements, and strong political sensitivity.
Since mobilization, the project department has adhered to normalized and standardized construction and advanced all work in an orderly manner. To overcome the difficulties of crossing complex strata and passing alongside the reservoir and power tower, it has repeatedly invited the five responsible parties to assess the characteristics of the surrounding rock at the tunnel face and organize discussions on construction plans. Construction is carried out strictly in accordance with the principles of the New Austrian Tunnelling Method; by reducing explosive charge, controlling advance per round, increasing monitoring frequency, and strengthening blasting vibration velocity monitoring and control, safe and controllable blasting construction is ensured. Throughout construction, the project has consistently upheld Shenzhen Metro's "model-led" concept, actively implemented the first-article system, strictly controlled project quality, and strictly controlled each process. It analyzes and summarizes in real time the on-site process coordination, construction techniques, construction safety and quality, surrounding rock conditions at the tunnel face, and changes in monitoring data, thereby improving management efficiency. It strictly implements the "pre-event, in-process, and post-event" three-investigation requirements for tunnel engineering construction, carries out routine ground patrol inspections, fully utilizes a comprehensive forecasting management system including ground-penetrating radar, transient electromagnetic method, and advanced drilling, and fully applies geophysical prospecting means to detect hidden underground cavities. Multi-frequency cavity detection is conducted for sections with construction anomalies, achieving early discovery and early elimination of risks and hidden dangers, effectively ensuring construction safety.
The smooth and timely holing-through of the connecting-line tunnel has accumulated valuable experience for the company in mining-method mined construction and further demonstrated the company's construction capability and technical level. Next, the project department will continue to keep safety tightly in focus, aim for the safe holing-through of the entire section, vigorously strengthen construction safety control, and go all out to achieve the project construction goals, promoting the high-quality development of Shenzhen Metro construction.
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