On May 29, a "steel giant" with an excavation diameter of 14.57 meters, equivalent to the height of a 5-story building, was officially unveiled in Changsha, Hunan. The "Jiaoping No. 1" super-large diameter shield machine, jointly developed by China Railway 11th Bureau Group and CRCHI, officially rolled off the production line. It will be deployed for the construction of the Mangshan Tunnel on the Jiaozuo-Pingdingshan Railway—the world's largest diameter earth pressure balance shield high-speed rail tunnel. This marks a new milestone for China's earth pressure balance shield technology in the field of high-risk, long-distance, and mixed-face tunnel construction.

"One Large, Two Longs, Three Difficulties": Why the Mangshan Tunnel is So Challenging

The Mangshan Tunnel on the Jiaozuo-Pingdingshan Railway, the target project for "Jiaoping No. 1," is the controlling engineering section of the entire line, facing extreme challenges summarized as "One Large, Two Longs, Three Difficulties."

"One Large" refers to the super-large cross-section. The tunnel adopts a single-tube double-track design with an excavation diameter of 14.57 meters and a cross-sectional area exceeding 167 square meters, making it the world's largest diameter earth pressure balance shield high-speed rail tunnel currently.

"Two Longs" refers to the ultra-long distance. The shield tunneling section is 4,970 meters long in total, with a single-heading advance of nearly 5 kilometers, making it one of the longest tunnels in the world using this construction method. Once the shield machine enters the ground, it will continuously excavate for several years without any possibility of mid-way withdrawal.

"Three Difficulties" refers to the overlapping challenges. The shield machine must traverse multiple mixed-face strata including clayey loess, silty clay, coarse gravel soil, and calcareous cemented layers, with localized sections containing boulders up to 30 centimeters in diameter. Simultaneously, it must underpass major risk sources such as the core protection area of the Mangshan Tomb Complex, the Jiaozuo-Liuzhou Railway, and the Lianhuo Expressway. Surface settlement must be strictly controlled to the millimeter level, presenting a construction difficulty rarely seen domestically.

Even more challenging is that the launching shaft has a longitudinal distance of only 54 meters, an extremely narrow site, necessitating a split launch for the super-large diameter shield machine—allowing this hundred-meter-long behemoth to start excavating module by module within the limited shaft space.

Comprehensive Customization from Cutterhead to AI

To address these extreme challenges, the R&D team spent over two years tailoring multiple core technological innovations for "Jiaoping No. 1."

1. China's First Cutterhead Specifically for Soft-Hard Composite Cemented Strata

During later detailed surveys, the construction team discovered large areas of calcareous cemented layers and boulders—a type of strata for which there was no mature experience in super-large diameter shield construction domestically. The team quickly initiated a major adjustment to the cutterhead design, completing the upgrade within 2 months, and created China's first super-large diameter shield cutterhead adapted for soft-hard composite cemented strata.

This cutterhead adopts a composite structure with 8 main spokes and 8 panels, featuring an opening ratio of 46%. The cutting tool system employs a combination of "disc cutters + ripper teeth + cutting knives," fully armed: 61 units of 19-inch single-disc cutters (specializing in hard rock), 14 wear-resistant ripper teeth (for cemented layers), and 104 toothed wide cutting knives (for soft soil cutting). The integration of three tool types achieves full coverage for special strata like soft soil and cemented layers.

For highly abrasive strata, the cutterhead surface is covered with chromium carbide composite wear-resistant plates, improving wear resistance by 40% and significantly extending the cutterhead's service life. Meanwhile, 20 soil conditioning injection ports are arranged on the cutterhead, working in conjunction with active mixing bars, a central agitator, and a high-pressure flushing system to effectively prevent clay clogging inside the cutterhead—a common technical challenge in highly viscous loess strata.

2. Multi-Layer Composite Grouting System Ensures Millimeter-Level Settlement

Controlling surface settlement to the millimeter level is the paramount requirement for the Mangshan Tunnel construction—because directly above the tunnel path lie the core protection area of the tomb complex and existing railways and highways.

The multi-layer composite grouting system equipped on "Jiaoping No. 1" has a total grouting capacity of 100 cubic meters per hour, enabling high-strength reinforcement of the surrounding rock synchronously during excavation. Measured data indicates that this system can precisely control surface settlement within the millimeter-level range required by the design, providing a fundamental guarantee for traversing multiple risk sources.

3. Synchronous Thrust and Erection System Boosts Efficiency by Nearly 30%

The time for a single ring cycle—excavating one ring and erecting one ring of segments—directly impacts the overall tunnel breakthrough speed. The synchronous thrust and erection system equipped on "Jiaoping No. 1" compresses the single-ring construction time from the traditional 127 minutes to 97 minutes, improving efficiency by nearly 30%. This means that for every kilometer excavated, several days of construction time can be directly saved.

Intelligent Leap: From "Experience-Based Construction" to "AI-Driven"

If the cutterhead and grouting represent "hard power," then the AI intelligent control platform represents "soft power." The combination of both constitutes a truly "smart shield machine."

The integrated shield AI intelligent control platform on "Jiaoping No. 1" can collect massive amounts of excavation data in real-time—dozens of key parameters such as thrust, torque, rotation speed, earth pressure, and grouting volume can all be automatically monitored, alerted, and regulated. Once the system identifies an abnormal trend, the AI can issue an alert within milliseconds, assisting operators in promptly adjusting the excavation strategy and eliminating potential risks before accidents occur.

Simultaneously, the system features intelligent fault diagnosis, enabling rapid localization and diagnosis of anomalies in the shield machine's various mechanical, electrical, and hydraulic systems, significantly shortening troubleshooting time and ensuring construction continuity and safety.

China's Large Shield Machines Advance to the World Summit

The rollout of "Jiaoping No. 1" carries threefold landmark significance.

First, a "World First" in technical terms. The three core parameters—an excavation diameter of 14.57 meters, a total weight of 3,500 tons, and an installed power of 10,000 kilowatts—push the world record for earth pressure balance shields to a new height. Among its many advanced technologies, the synchronous thrust and erection system shortens single-ring operation by 30 minutes, cutterhead wear resistance improves by 40%, and the AI platform enables full-time intelligent monitoring—each innovation is a natural culmination of the technological accumulation in domestically produced large shield machines.

Second, "Cross-Industry Integration" in industrial significance. In recent years, as China's high-speed rail network continuously extends into geologically complex regions, the application of super-large diameter shield machines in railway tunnels has become increasingly widespread. "Jiaoping No. 1" fills the gap for earth pressure balance shields in the special working condition of soft-hard composite cemented strata, providing reliable large-diameter excavation equipment support for China's high-speed railways traversing major river valleys and urban agglomerations.

Third, "Heluo Sentiment" in cultural significance. The cutterhead livery of "Jiaoping No. 1" features the theme of the "Dragon Horse," inspired by the myth of the "River Map"—in ancient times, a dragon horse emerged from the Yellow River bearing a star chart on its back, from which Fuxi drew the Primordial Eight Trigrams, initiating the Heluo civilization. The image of the dragon horse prominently centered on the cutterhead not only carries the millennia-old symbolism of protecting the Heluo region but also embodies the builders' firm belief in rooting themselves in the Heluo land and overcoming difficulties.

Construction Timeline and Outlook

According to Chen Jian, project manager of the Mangshan Tunnel on the Jiaozuo-Pingdingshan Railway for China Railway 11th Bureau Group, after leaving the factory, "Jiaoping No. 1" will be disassembled into over a hundred components and transported to the construction site via specialized transport. Currently, the launching shaft and supporting works are basically ready. After the equipment arrives on site, a professional team of over 80 people will organize assembly and commissioning, with the official launch and excavation expected by the end of July.

This "Dragon Horse" behemoth setting out to conquer Mangshan carries not only the weight of millions of tons of steel but also the determination of China's construction machinery industry to leap towards high-end, intelligent, and unmanned operations. From "Made in China" to "Created in China," the technical discourse power in the field of earth pressure balance shield machines is steadily returning to the hands of Chinese engineers.