"Golden Shield" Completed Three Months Ahead of Schedule: Shu'an Tunnel of Chengdu-Chongqing Midline High-Speed Railway Surpasses 80% Excavation Progress

On the morning of December 1, at the precast segment factory in Qingbaijiang District, Chengdu, the final segment for the Shu'an Tunnel of the Chengdu-Chongqing Midline High-Speed Railway project was lifted into place by an overhead crane, marking its completion three months ahead of schedule.

The tunnel boring machine (TBM), a critical tool for excavation, features a robust cutting head designed to break through hard rock and soil. During construction, the TBM periodically pauses to assemble precast concrete segments, ensuring the tunnel is built simultaneously with excavation. With the final segment cast, production for the Shu'an Tunnel’s shield segments is now complete, accelerating subsequent construction.

**Full-Speed Production to Meet Deadlines** Inside the spacious factory, an intelligent steel processing line handles tasks such as cutting, bending, and welding to form the segment "skeleton." On the left, automated production molds move along an oval track, undergoing cleaning, reinforcement placement, and concrete pouring—each segment taking just five to six minutes to form.

Post-production, segments undergo a 10-hour steam cure, followed by water immersion and spray curing to enhance strength and prevent cracks. These precision-engineered segments, forming a "golden shield," are vital for tunnel integrity and safety.

Li Yong, head of the Qingbaijiang segment factory under China Railway 11th Bureau, explained that each ring consists of 10 curved segments, with 4,919 rings required for the tunnel. The project involves two segment types (13.5m and 14m inner diameters), demanding meticulous coordination.

**Smart Factory Boosts Efficiency by 20%** Designed as a cutting-edge intelligent facility, the factory employs automation and a proprietary smart management system. Workers now number just 34 (down from 91), with productivity rising by 20%. A central control room monitors all processes, ensuring dimensional accuracy within 1mm for individual segments and 2mm for assembled rings.

Innovations include 3D modeling and virtual ring assembly tests, reducing inspection time from three days to one hour. This system, a first in China’s precast segment industry, enhances quality through digital-physical cross-verification.

**Project Progress and Broader Impact** The Shu'an Tunnel has advanced 8,380m (80% completion). Other key projects, like the Longquanshan Tunnel and Tuojiang Bridge, are also on track.

Scheduled for completion in 2027, the 292km Chengdu-Chongqing Midline High-Speed Railway (350km/h design, 400km/h potential) will slash travel time between the two cities to 50 minutes. It will integrate with existing and planned lines, including Xi'an-Chengdu and Chongqing-Kunming routes, bolstering regional connectivity.

*Images provided by China Railway 11th Bureau’s Qingbaijiang segment factory.*