Workers are seen at the construction site of the Yangshan Tunnel, part of the Menghua Railway, in Yan'an, northwest China's Shaanxi Province, Aug. 10, 2018. The construction of the 11.668-km tunnel was completed here Friday. (Xinhua/Zhang Bowen)

Photo taken on Aug. 10, 2018 shows the construction site of the Yangshan Tunnel, part of the Menghua Railway, in Yan'an, northwest China's Shaanxi Province. The construction of the 11.668-km tunnel was completed here Friday. (Xinhua/Zhang Bowen)

Photo taken on Aug. 10, 2018 shows the construction site of the Yangshan Tunnel, part of the Menghua Railway, in Yan'an, northwest China's Shaanxi Province. The construction of the 11.668-km tunnel was completed here Friday. (Xinhua/Zhang Bowen)

Workers celebrate as they complete the construction of the Yangshan Tunnel, part of the Menghua Railway, in Yan'an, northwest China's Shaanxi Province, Aug. 10, 2018. The construction of the 11.668-km tunnel was completed here Friday. (Xinhua/Zhang Bowen)

Workers are seen at the construction site of the Yangshan Tunnel, part of the Menghua Railway, in Yan'an, northwest China's Shaanxi Province, Aug. 10, 2018. The construction of the 11.668-km tunnel was completed here Friday. (Xinhua/Zhang Bowen)