On November 14, the reporter learned from Hefei Rail Transit Group that the dual-line shield tunneling section from Lingbi Road Station to Yaoyuan Road Station on Phase I of Line 8 has been successfully completed, marking Hefei's first completed stacked (overlapping) tunnel section.

The "Lingyao" section is approximately 2,000 meters long and runs north-south along the Fuyang North Road elevated expressway. During excavation, it successively passed beneath many high-risk sources such as railways and high-speed rail bridge piles, as well as numerous structures and buildings.

Because the center of the section intersects with the railway track group in both plan and space, in order to smoothly pass beneath the elevated bridge and the railway track group, Hefei Rail Transit led the design unit to break away from the conventional approach of designing parallel left and right dual-line shield tunnels, and instead changed the tunnel section in the narrow construction area to a stacked upper-and-lower design, effectively reducing the underground space footprint and improving space utilization. Therefore, on the drawings, the right shield tunnel line "vanishes into thin air" from ring 718 and does not reappear until ring 1248. The stacked section spans 693 meters, a length rarely seen in China. At the same time, the minimum vertical spacing between the two stacked shield tunnels is only 4 meters, and settlement data control is extremely stringent, making this the section with the highest risk, the most complex construction environment, and the greatest difficulty in the shield tunneling construction of Line 8.

To accomplish this unprecedented "underground crossing," Hefei Rail Transit led the participating construction units to set up a trial section before formal excavation, collect detailed real-time data, hold technical seminars, formulate practical and feasible construction plans, strictly control construction safety, quality, and settlement data, and reasonably select segment assembly points, successfully completing the safe and smooth underpass of the shield machine, with "zero" settlement of the road surface and structures.

In addition, during the shield machine's underpass of risk sources, 16-hole "multi-hole grouting segments" were used to reinforce the surrounding tunnel, compared with traditional 6-hole "grouting segments," the gaps between the tunnel and the soil are smaller, ensuring safe and orderly progress of shield construction.

Up to now, the main structures of all 12 stations on Phase I of Line 8 have been capped, and 23 of the 24 single-line shield tunnel sections have been completed.