On July 16, as the cutterhead of the boring machine slowly rotated, the "Qinglong" dual-shield earth-pressure combined boring machine successfully launched on the left line of the Tianshan Er Road Station–Nanwan Station section of the first phase of Qingdao Metro Line 15, constructed by China Railway 18th Bureau Group, marking that the construction of Qingdao Metro Line 15 has entered the "fast lane."

The first phase of Qingdao Metro Line 15 starts at Xiawangbu Station and ends at Sifangchang Station, passing through three districts of Licang, Chengyang and Jimo, with a main line length of about 30.8 kilometers and 17 stations. Among them, the Tiannan section tunnel has a total length of 2.92 kilometers, with a maximum buried depth of 30 meters at the tunnel crown and a complex surrounding environment. The section passes beneath the subgrade sections of the Qingdao-Rongcheng Intercity Railway and the Jiaozhou-Jinan Passenger Dedicated Line, where the shield tunneling method is required, involving great construction difficulty and high requirements, which is the first case of its kind in Shandong Province.

To ensure safe construction, the project team analyzed and summarized the tunneling parameters of similar past projects and strata, further drew on the technical experience of shield machines passing beneath structures, and customized the "Qinglong" dual-shield earth-pressure combined boring machine. This equipment is based on a dual-shield TBM, with research and modification adding a pressure-maintaining tunneling function, and can switch modes on site according to geological conditions; this application is the first of its kind in the field of urban rail transit in China. Compared with traditional dual-shield TBMs, it has higher adaptability to strata and can stabilize the soil in front of the cutterhead through pressure maintenance and control groundwater discharge; compared with traditional shield machines, it has stronger rock-breaking capability and higher construction efficiency, laying a solid foundation for the safe and smooth progress of the project.

It is reported that after the completion of the first phase of Qingdao Metro Line 15, it will not only connect with Qingdao Metro Line 2 and Line 3, alleviate traffic pressure along Heilongjiang Road, and open up a major north-south corridor in Qingdao, but will also link the two major urban areas on the east bank and the north bank, helping Chengyang enter the "main city era" and creating important transportation conditions for a breakthrough in Qingdao's urban layout.