On August 28, the 120-meter-long "underground giant," after more than 40 days of hoisting, lowering into the shaft, and assembly, set off from Luomashi Station on Phase III of Line 18—the deepest station of the Chengdu Metro—and advanced toward Sheng Tiyuguan (Provincial Gymnasium) Station.

Multiple hoisting operations

The "giant" first splits apart, then joins together

At the construction site, the reporter saw a 500-ton crawler crane more than ten meters tall standing on one side of the launch shaft. It was the "main force" behind this shield launch.

"This 'Zhuoyue' shield machine has a diameter of 8.6 meters and a total length of 120 meters; the heaviest part of the entire machine, the drive section, weighs 130 tons," Li Peng, deputy shield manager of the civil works Section 1 of the Phase III Line 18 project under China Railway 18th Bureau Group, told the reporter.

Because the site is located in Luomashi in the core area of Chengdu, with many tall buildings nearby, and is constrained by on-site construction conditions, the "Zhuoyue" could not be lowered underground through a single shaft opening. Instead, the shield body serving as the "head" was lowered through the launch shaft on the left line, while the shield machine's trolleys serving as the "body" were lowered underground through the adjacent shaft on the right line, then pushed by jacks to the launch shaft to join with the "head."

"The entire hoisting and assembly took more than 40 days in total," Li Peng said. After the launch of the "Zhuoyue," three more shield machines will successively be lowered into the shaft and launched at this station, boring at full speed toward the north and south respectively.

The deepest station

Equivalent to 15 stories underground

As Chengdu's first four-line interchange station and the only one currently under construction, the Luomashi stations for Line 1 and Line 4 have already been completed, while those for Line 18 and Line 10 are under construction.

"Because it is a four-line interchange station and Line 18 is at the very bottom, the station is exceptionally deep," Luo Jie, deputy director of the Project Management Center I of Chengdu Rail Construction Management Co., Ltd., told the reporter. From top to bottom, the four lines at Luomashi Station are Line 1 at a depth of about 17 meters, Line 4 at about 24 meters, Line 10 at about 35 meters, and Line 18 at a maximum depth of 45.5 meters.

"What does 45.5 meters deep mean? If the height of one story is calculated at 3 meters, 45.5 meters is equivalent to 15 stories underground." According to the introduction, a subway station this deep is not only "the deepest in Chengdu" but also rarely seen nationwide.

Highly demanding on skill

Settlement must be kept within 4 millimeters

The shield section for the "Zhuoyue" starts at the large-chainage end of Luomashi Station, runs south along Renmin Middle Road, and ends at the intermediate ventilation shaft between Luomashi and Sheng Tiyuguan, with a length of about 1,955 meters.

"The minimum cover depth of this section is about 34.3 meters and the maximum cover depth is about 54.7 meters, making it the ultra-deep tunnel with the largest average cover depth in Chengdu's rail transit system. The entire boring alignment forms a 'V' shape," said Huang Guangkai, project manager of the civil works Section 1 of the Phase III Line 18 project under China Railway 18th Bureau Group.

According to the introduction, the shield will pass over a long distance beneath existing operating lines of Line 1 and Line 2, including Tianfu Square Station, Jinjiang Hotel Station, and the running tunnels between them. During the crossing, the differential settlement of the existing track surfaces must be kept within 4 millimeters—shorter than the length of a grain of rice.

It is understood that the tunnel in this section is expected to break through in August next year.