A worker is busy at the construction site of the Wushan tunnel of the Zhengzhou-Wanzhou high-speed railway in Wushan County, southwest China's Chongqing, Dec. 15, 2020. The 16.571 km Wushan tunnel was successfully drilled through on Tuesday. (Xinhua/Tang Yi)

A truck runs out of the Wushan tunnel of the Zhengzhou-Wanzhou high-speed railway in Wushan County, southwest China's Chongqing, Dec. 15, 2020. The 16.571 km Wushan tunnel was successfully drilled through on Tuesday. (Xinhua/Tang Yi)

Construction workers celebrate the breakthrough of the Wushan tunnel of the Zhengzhou-Wanzhou high-speed railway in Wushan County, southwest China's Chongqing, Dec. 15, 2020. The 16.571 km Wushan tunnel was successfully drilled through on Tuesday. (Xinhua/Tang Yi)

A worker is busy at the construction site of the Wushan tunnel of the Zhengzhou-Wanzhou high-speed railway in Wushan County, southwest China's Chongqing, Dec. 15, 2020. The 16.571 km Wushan tunnel was successfully drilled through on Tuesday. (Xinhua/Tang Yi)