A worker maintains a tunnel boring machine in a tunnel below ground of the Qinling Mountains in northwest China's Shaanxi Province, Feb. 4, 2021. More than 60 workers stick to their posts working in three shifts a day to guarantee the on-schedule of completion of the tunnel. Upon completion, water from the Hanjiang River, a major tributary of the Yangtze River, will flow through the 9,830-meter-long tunnel to the Weihe River, a tributary of the Yellow River, to ease water supply strains in central Shaanxi. (Xinhua/Liu Xiao)

Workers maintain a tunnel boring machine in a tunnel below ground of the Qinling Mountains in northwest China's Shaanxi Province, Feb. 4, 2021. (Xinhua/Liu Xiao)

A worker maintains a tunnel boring machine in a tunnel below ground of the Qinling Mountains in northwest China's Shaanxi Province, Feb. 4, 2021. (Xinhua/Liu Xiao)

A worker maintains a tunnel boring machine in a tunnel below ground of the Qinling Mountains in northwest China's Shaanxi Province, Feb. 4, 2021. (Xinhua/Liu Xiao)