On January 20, the shield machine for the right line of the shield-driven section from Shiqiao Station to Zhongyi Road Station (hereinafter referred to as the Shi-Zhong section) of Wuhan's first metro loop line, Line 12, successfully passed beneath Shiqiao Station of Line 6, marking that the shield machine has successfully overcome a Level-1 risk source and officially begun its "underground journey."

Shiqiao Station of Line 12 is located on the east side of the intersection of Gusaoshu Road and Houhu Avenue, with a total length of 186 meters, a standard width of 22.7 meters, and a width of 27 meters at the end-shaft section. With a depth of about 32 meters, equivalent to the height of an 11-story building, it is the deepest station under construction on the Wuhan Metro and will, once completed, provide a transfer with the already-operating Shiqiao Station of Line 6.

The shield machine of the Shi-Zhong section had to pass beneath Line 6 right after "starting off." The section is located on the first-level terrace of the Yangtze River, in water-rich soft soil strata, imposing extremely high requirements on tunnel settlement control. Qin Yazhou, an engineer from the Quality and Safety Supervision Department of Wuhan Metro, explained that in order to protect the existing operating line during construction while allowing the line under construction to pass through smoothly, the project department invited industry experts to repeatedly review the construction plan and to formulate, step by step, the shield tunneling parameters and control indicators for the underpass. At the same time, they adopted the shield launching technique with the highest safety factor currently available—steel sleeve launching.

What is steel sleeve launching? Li Feipeng, project manager of the contractor China Railway 11th Bureau Group, explained that it means enclosing the shield machine in a sealed steel sleeve, keeping it enclosed within, to create a safe launching environment for it, so that during the launching stage it can tunnel entirely with normal parameters, ensuring safe entry into the tunnel.

To ensure on-site construction quality, Wuhan Metro Group, China Railway Construction Investment Group, and the construction unit implemented graded risk control, with 24-hour on-site monitoring. "We also established a simulation platform to review the entire construction process through simulation. In particular, when the shield machine passes through major risk sources, we carry out simulated-section tests in advance, summarize the data from the test stage, and only then carry out the actual crossing," Li Feipeng explained. Shiqiao Station has four shield machines launching—two heading toward Zhongyi Road Station and two toward Hankou Railway Station—all of which will use steel sleeves.