After six years of construction, a tunnel along the Chengdu-Lanzhou high-speed railway was announced as "dug through" on Sunday. Crossing the active fault zone of the Longmen Mountains, the 9,913-meter Maoxian Tunnel, located in the Aba Tibetan and Qiang Autonomous Prefecture in southwest China's Sichuan Province, is one of the key projects and the most challenging part of the railway line's construction.