On February 10, reporters came to Baguazhou in the Nanjing section of the Yangtze River to visit the right-line project of the Nanjing Heyan Yangtze River Crossing Tunnel. This is the first time a super-large-diameter atmospheric cutterhead tunnel boring machine independently developed by China has been used on the Yangtze River.

According to Li Tengjiao, manager of the Nanjing Heyan Yangtze River Crossing Tunnel project department of CCCC Tianhe, which is responsible for the shield tunneling, this "Zhenxing" tunnel boring machine has a diameter of 15.03 meters, is as tall as a five-story building, has a total length of 153 meters and weighs 4,000 tonnes. Like a giant dragon crossing the river, it has been tunneling underground for more than a year and is now only about 100 meters from Yanziji on the south bank of the Yangtze.

Reporters drove in from the north portal of the tunnel. The tunnel wall is assembled from precast concrete segments. The tunnel boring machine has now advanced 1,878 meters, with its deepest point 79 meters below the river surface, and has successfully passed through special geological environments such as the Yangtze River levee and fault zones.

Li Tengjiao reminded reporters: "Look carefully. There is no water mark in the gaps between the segments, which shows that the intelligent assembly precision of our tunnel boring machine is very high and effectively prevents groundwater seepage."

The more than 150-meter-long giant involves complex processes such as cutterhead excavation, slurry flushing and segment installation. Reporters had originally thought that at least a dozen people would be needed to operate it in shifts, but unexpectedly the control room is only a few square meters, with just two technicians monitoring the console.

"This domestic tunnel boring machine is the first to adopt independent technologies such as cutter replacement under atmospheric pressure and full-condition monitoring of cutters, many of which have reached internationally leading levels. During construction, it also set a domestic record of tunneling 1.5 kilometers without changing cutters," Li Tengjiao said.

Seeing that the tunnel boring machine was carrying out cutter replacement, reporters crouched and walked through a passage more than half a meter high to the very front of the machine, where two young men wearing blue special-operation helmets were removing cutterhead components.

"We are now at standard atmospheric pressure and do not feel any discomfort. We can carry out work directly. This is the effect of applying atmospheric cutter replacement technology," said Zhu Jingshan, deputy chief engineer of the project department. A few years ago, domestic tunnel boring machines did not yet master this technology. During cutter replacement, high pressure had to be used to counter the weight of the soil, and personnel working in a high-pressure environment for half an hour had to spend four hours in a decompression chamber.

"Atmospheric cutter replacement greatly improves the efficiency of cutter replacement operations and, more importantly, ensures personnel safety," Li Tengjiao told reporters. This year, 125 people in the project department are celebrating the Spring Festival locally. They have organized activities such as basketball games and cooking competitions, and will fully resume work on the fourth day of the first lunar month. They are expected to reach the south bank of the Yangtze in March.