At around 9 a.m. on September 1, with the construction workers' final blasting operation, after more than 1,260 days of construction, the Zhongling Tunnel—the last tunnel on the Chongqing East to Qianjiang section of the Chongqing-Xiamen High-Speed Railway (formerly the Chongqing East to Qianjiang section of the Chongqing-Xiangxi High-Speed Railway)—was successfully holed through, marking that all 50 tunnels and 82 bridges on the Chongqing East to Qianjiang section of the Chongqing-Xiamen High-Speed Railway have been fully connected, laying a solid foundation for the section to meet the conditions for opening to traffic in 2025.

Construction site of the Zhongling Tunnel on the Chongqing East to Qianjiang section of the Chongqing-Xiamen High-Speed Railway.

The Zhongling Tunnel is located in Wulong District, Chongqing, with a total length of 7,423 meters, and is a controlling project of the entire line. The tunnel mainly passes through gas-bearing coal seams, cliff-type karst caves, bead-string-type karst caves, irregular dissolution fissures and underground rivers. During construction, unfavorable geological conditions such as bedding-parallel slope at the portal, karst, gas, large deformation of soft rock and rockburst were encountered, posing extremely high safety risks and construction difficulties.

According to reports, the unfavorable geology of the Zhongling Tunnel is comparable to a "geological museum." In response to the potential risks in tunnel construction, the construction personnel adopted comprehensive geological prediction methods such as advanced detection using the RPD-180CBR multifunctional drilling rig, and employed advanced equipment, construction methods and safety control measures including the KJ90X automatic gas detection system, the cantilever multifunctional excavation bench, the 36-meter self-propelled hydraulic trestle bridge, and the Model 450 low-headroom rotary drilling rig for hole formation. They persisted in carrying out advanced prediction and strengthening monitoring and measurement, ascertained engineering geological and hydrogeological conditions in advance, and organized construction scientifically around the principle of "adapting to changes in rock conditions," overcoming difficulties such as ultra-large karst collapse and inrush, gas safety prevention and control, rockburst at ultra-large burial depth, karst treatment at the tunnel bottom over ultra-long sections, and deep-hole pile foundation construction of nearly 47 meters inside the tunnel, ensuring the safe and smooth holing-through of the tunnel.

It is understood that after the line is completed, the travel time from the central urban area of Chongqing to Qianjiang District will be shortened from the current 4 hours to less than 1 hour, which will further strengthen the interconnection between the areas along the line and economically developed regions such as the West Coast Economic Zone of the Taiwan Strait and the urban agglomeration in the middle reaches of the Yangtze River. It is of great significance for integrating tourism resources along the line, accelerating the development of the "greater tourism economy" in the areas along the line, and promoting the rapid socio-economic development of the region.

At present, on the Chongqing section of the Chongqing-Xiamen High-Speed Railway, only the Chongqing Caiyuanba Yangtze River Railway Tunnel from Chongqing to Chongqing East has not yet been holed through, and construction is progressing steadily according to the construction plan.