On the morning of February 10, after more than 1,290 days and nights of arduous construction, the left tube of the Tanbaoshan Tunnel on the Chongqing-Wuxi Expressway, built jointly by China Railway 12th Bureau Group and China Railway 15th Bureau Group, was successfully holed through.

The Wuxi Expressway starts in Wuxi County, Chongqing, and ends in Zhenping County, Shaanxi Province, with a total length of 48.69 km. It is being built to a two-way, four-lane expressway standard, with a bridge-tunnel ratio of 90.6%. It is the second expressway corridor directly linking Chongqing and Shaanxi, and currently the expressway with the highest bridge-tunnel ratio in Chongqing. Construction began on November 27, 2018, and it is scheduled to open to traffic in 2023. By then, the drive between Wuxi, Chongqing, and Zhenping, Shaanxi, will be shortened from 3.5 hours to less than 1 hour.

The Tanbaoshan Tunnel is 4,616 meters long and is designed as a two-tube, two-way, four-lane tunnel, with a clear width of 10.25 meters and a clear height of 5 meters for the main tube. It is a gas tunnel and a key controlling project on the entire line. The tunnel portal is located below the riverbed of the Zhongba River, which flows year-round, and the tunnel crown is only 2 meters from the riverbed bottom, making entry conditions extremely difficult. After entering the tunnel, the project also faced special and complex geological conditions such as water inflow, gas, karst, and mined-out areas. The exit portal is located in high mountains and deep valleys and connects to the Dongxi River Grand Bridge, posing great construction difficulties.

During construction at the tunnel portal, China Railway 15th Bureau Group equipped the tunnel entrance with intelligent systems such as access control, personnel positioning, video surveillance, gas monitoring, and wired broadcasting to ensure construction safety, empowering construction production through smart construction. To address high-voltage electrical safety, they adopted a TN-S system for power use outside the tunnel and an IT system inside the tunnel, with all transmission lines using mining explosion-proof flexible cables, and electrical equipment, switches, and lighting fixtures selected to reduce safety risks. To solve the problem of the tunnel passing beneath the river channel under complex geological conditions, the project leadership team took turns on site around the clock. Through measures such as river channel relocation, surrounding rock reinforcement grouting, and advanced pipe roof installation, they increased construction crews and machinery and equipment input and worked continuously day and night, achieving a monthly advance of 70 meters in Grade V surrounding rock and greatly shortening the construction schedule.

In September 2022, after gas was detected during construction at the tunnel exit by China Railway 12th Bureau Group, they immediately used technical means such as TSP long-distance geophysical prospecting, advanced geological drilling, advanced core drilling, and deepened blast holes to determine the thickness and dip angle of the coal seam ahead and its spatial relationship with the tunnel. Based on the results of advanced geological forecasting and gas identification reports, they formulated special construction plans. By strictly implementing access control, modifying explosion-proof equipment, and increasing tunnel ventilation and gas detection, they safely penetrated the coal seam, laying a solid foundation for the breakthrough of the Tanbaoshan Tunnel.