The shield machine of the Ding-Shi section of Line 12 exits the tunnel with precision.

On July 11, as the final tail shield segment of the "Pioneer" shield machine was lifted out at Shilipu Station, the tunnel of the Ding-Shi section (Dingjiazui Station–Shilipu Station) of Wuhan Metro Loop Line 12 achieved a double-line breakthrough. The construction team forged ahead with innovation, and a breakthrough was made in the construction technology for the shield machine successfully passing beneath an existing station and its retaining piles.

According to a Wuhan municipal model worker, this section is a key and difficult control project of Metro Line 12. In a shield-driven section of only 870 meters, the shield machine had to overcome three major challenges: boring through hard rock, passing under a bridge, and crossing beneath a station. To effectively reduce tunneling risks and ensure construction quality and progress, Wuhan Metro Group and the contractor China Railway Seventh Group conducted repeated demonstrations and joined forces with the manufacturer and research institutions, enabling the shield machine to achieve ample power, wear resistance, and high flexibility in complex geological environments, handling both soft and hard ground and boring through in one go.

Boring through hard rock. After advancing 150 meters, the shield machine encountered a 274-meter section of moderately weathered quartz sandstone hard rock with a strength of 214 MPa, making tunneling like drilling through a steel plate. The project department promptly replaced the cutterhead and equipped it with full-face disc cutters whose blade compressive strength reached 2,800 MPa, achieving the effect of "cutting iron like mud," and broke through the difficult stretch in one month.

Passing under a bridge. When the shield machine passed alongside the Second Ring Road elevated bridge, the minimum horizontal distance from the bridge piles was only 1.8 meters, making tunneling like walking a tightrope—a slight misstep could cause deviation from the alignment. Before the crossing construction, a trial section was set up to determine the optimal tunneling parameters and reduce disturbance to the bridge piles from tunnel construction. An automated monitoring system was used to monitor pier settlement data in real time, with manual verification of tunnel structure changes, achieving near-zero settlement in the side-crossing bridge construction.

The final tail shield segment of the shield machine is lifted out, marking the double-line breakthrough of the Ding-Shi section tunnel.

Crossing beneath a station. To avoid vibration from shield tunneling disturbing Line 4 operations, the shield machine advanced during the maintenance window from 0:00 to 4:30 a.m. During tunneling, intelligent robots scanned the entire process and submitted a monitoring report every half hour; the shield machine adjusted tunneling parameters based on the monitoring results and successfully passed beneath Line 4 in five days, with no abnormalities in the station structure. This set a precedent for a shield machine fully passing beneath a single station on Wuhan Metro and provided a safer and more efficient reference method for subsequent line construction.

Ni Zhengmao, who has directly participated in the river-crossing shield tunneling of Wuhan Metro Lines 2, 3, 4, 7, and 12, said that the double-line breakthrough of the Ding-Shi section tunnel has accumulated practical experience and driven continuous new breakthroughs in the construction technology of shield tunnels passing beneath existing metro stations and retaining piles, with shield construction technology becoming increasingly mature.