On April 20, as the cutterhead of the "Jiaozhou Bay No. 7" shield machine broke through the soil, the right line of the Qidian–Dajian Station section of the Qingdao Metro Line 8 Branch, constructed by CCCC First Harbor Engineering Co., Ltd., was successfully holed through, marking that the **shield-driven tunnel section of the Qingdao Metro Line 8 Branch has achieved single-line breakthrough.

The tunnel holed through this time is the right line of the Qidian–Dajian Station section, with a length of about 500 meters, facing a complex construction environment and multiple technical challenges. On the one hand, the shield machine had to pass through slightly weathered rock strata, where the rock in the excavation section was hard, with a maximum strength of up to 133 MPa; on the other hand, the shield machine was launched on a curve with a radius of 450 meters and had to continuously turn and change gradients; in addition, the shield machine had to pass beneath high-pressure gas pipelines, cross over and run parallel to existing operating metro lines with a minimum clear distance of only 3.8 meters, and also pass beneath a rainwater box culvert with a minimum clear distance of 4.9 meters. The construction environment involved numerous and complex risks, and the construction risk was extremely high.

To achieve the target objectives safely, with high quality and efficiently, since the shield launch, under the supervision of the Qingdao Municipal Public Utility Engineering Quality and Safety Supervision Station, and with the strong support of Qingdao Metro Group Co., Ltd., the Operating Company, the Third Construction Branch Company, the consortium of China Railway Jinan Engineering Construction Supervision Co., Ltd. and Qingdao Xinda Engineering Management Co., Ltd., and all participating units, the project team of CCCC First Harbor Engineering Co., Ltd. formulated detailed construction plans and organized construction scientifically. The project team selected a shield machine with powerful excavation capability and high wear resistance, carefully selected cutters, and optimized the cutterhead in a targeted manner, carrying out only one stoppage for cutter replacement throughout the entire process, ensuring safe and efficient excavation of the shield machine in the slightly weathered rock strata; the project team selected and strengthened professional management personnel and labor teams, strengthened the guarantee of equipment, materials and other elements, and continuously strengthened the training and skill improvement of technical personnel, so that the shield machine could maintain high precision and stability during the continuous turning and gradient-changing process of launching on a 450-meter-radius curve, and the formed tunnel was impermeable and leak-free; in addition, the project team improved the safety management system and emergency plan system, refined construction technical disclosures and safety disclosures, carried out advanced geological forecasting multiple times during excavation, strengthened on-site safety monitoring and early warning, and jointly carried out emergency drills with the operating unit, ultimately achieving safe and precise breakthrough of the formed tunnel on the right line of the section.

Next, the project team will take this as an opportunity to accelerate the conversion of construction procedures, take multiple measures to ensure safety, guarantee quality and promote progress, and contribute to promoting the construction of a "double first-class" metro and building "Qingdao on Track."

The Qingdao Metro Line 8 Branch is a key implementation project of Qingdao's three-year action plan for urban renewal and urban construction, and is the first metro line in a county-level city in Shandong Province. It starts at Dajian Station of Line 8 and ends at Jiaozhou Railway Station, with a total length of about 20.4 kilometers. A total of 15 shield machines are planned to be deployed, and 13 shield machines have currently been successfully launched, with cumulative shield excavation exceeding 10,000 meters.