On July 12, the shield-driven section from Nantong Railway Station Station to Yongda Road Station on Section 03 of Rail Transit Phase I Project Line 2, constructed by China Railway 14th Bureau Group, was successfully completed. The "Zhiyun No. 11" shield machine undertaking the tunneling task safely crossed seven operating railway lines twice and kept the settlement value stable at 1.3 millimeters, achieving "zero settlement" in line with industry construction standards. This high-precision crossing was also the first dual-line "zero settlement" crossing of a high-speed railway passenger station since the opening of the "Shanghai-Suzhou-Nantong Railway."

"Zhiyun No. 11" Advances Another 1,026 Meters in 120 Days

At 15:30 on July 12, at the receiving shaft on the west side of Nantong Railway Station Station, the shield body of the "Zhiyun No. 11" shield machine had fully entered the steel sleeve with a diameter of 6.8 meters and a length of 10.5 meters, and the tunnel portal sealing was completed. At this point, the section from Nantong Railway Station Station to Yongda Road Station was successfully completed. Before reception, work such as end reinforcement, measurement and attitude adjustment, tunnel portal treatment, steel sleeve installation, removal of the retaining structure, and groundwater level control had to be carried out.

The "Zhiyun No. 11" shield machine was designed and manufactured by CRCHI and tailored for Nantong urban rail transit. This "steel earthworm" has a diameter of 6.44 meters, taller than a two-story building, a length of 84 meters, and a weight of 450 tons. The outside of the shield machine is a metal shell, inside which the complete machine and auxiliary equipment are installed. Under the protection of the shield shell, operations such as tunnel soil excavation, muck removal, complete machine advancement, and segment installation are carried out. "Zhiyun No. 11" started smoothly on the right line on March 14, 2021, and broke through on the right line on July 12, 2021. The right line took 120 days and advanced a total of 854 rings, completing all 1,707 rings of segments in the section.

Railway-related Procedures Handled Quickly, Far Exceeding Similar Railway-related Projects

This shield-driven section passes beneath seven tracks and three platforms of Nantong Railway Station and is a railway-related project. In handling railway-related procedures, there were problems such as many departments to coordinate with, high difficulty, complicated procedures, and long approval times.

The project department, together with the owner, communicated and coordinated with the railway department many times. On February 13, 2020, the railway-related approval document from the Shanghai Railway Bureau was received; on March 9, 2020, the reinforced agent construction agreement was signed; subsequently, more than 10 meetings were held, including construction drawing review meetings, scheme review meetings, line blockade coordination meetings, and on-site briefings with the four-electricity units. On-site railway-related reinforcement construction began on August 21, 2020.

It is understood that from the issuance of the approval document to the start of grouting reinforcement construction, the railway-related procedures took only 190 working days, far faster than similar railway-related projects, gaining initiative and seizing the opportunity for subsequent work.

"Zero Settlement" in Crossing Beneath Seven Railways

The strata in Nantong are mainly water-rich sand layers. In the shield crossing section, blowouts are very likely to occur, causing excessive settlement. Construction is difficult, safety risks are high, and there are many uncontrollable factors. In addition, the line in this section is designed as a small-radius curve of 600 meters, making shield attitude control difficult. The cumulative settlement control standard for the railway is 10 millimeters, with extremely high precision requirements.

To overcome the difficulties, the project department planned ahead and organized more than 20 expert demonstration meetings and construction seminars, continuously optimizing the scheme and resource allocation. Through processes and methods such as WSS + sleeve valve pipe grouting reinforcement and clay-shield effectiveness, the safety and controllability of the shield tunneling process were ensured. The most advanced automated deformation monitoring system in China was adopted to closely monitor settlement data along the line, strictly control various tunneling parameters, ensure timely and accurate feedback data, and prepare various emergency response measures in advance.

Third-party testing results show that after "Zhiyun No. 11" crossed beneath the Nanjing-Qidong Railway on the left line, the actual settlement was only 1.1 millimeters; after crossing beneath the Nanjing-Qidong Railway on the right line, the actual settlement was only 1.3 millimeters, less than the size of a hair, almost "zero settlement." This breakthrough was a high-precision breakthrough. In addition to crossing beneath the Nanjing-Qidong Railway, it also passed beneath major risk sources such as canopy column foundations and the drop-off platform, all very safely and smoothly.

Through the continuous efforts of the participating employees, "Zhiyun No. 11" achieved the good quality goals of small ground settlement in the shield-driven section, smooth segment assembly, and no leakage. At present, all segment assembly in this section has been completed.