A proposed solution to the ground fissure encountered in urban metro construction in Xi’an, China

The city of Xi’an, Shaanxi, China, was founded over 3000 years ago. However, the city faces urban geological hazards with 14 parallel ground fissures covering a wide area of the municipal area. The ground fissures are not only hazardous to surface buildings, structures and underground pipes but also pose a major safety risk to the 15 metro lines under construction or under planning. Such challenges are unprecedented in the history of metro construction around the world. Research indicates that the ground fissures in Xi’an produce three-dimensional motion, among which the vertical displacement has the strongest effects on metro engineering. The results of large-scale physical model tests suggest that damages such as cracks in tunnel lining, failures of waterproofing and deformation of metro rail can be caused by the activities of ground fissures. To mitigate such risks, this paper proposes a series of engineering countermeasures such as enlargement of tunnel sections to maintain clearance, use of segmented tunnels, enhancement of tunnel lining, and use of multiple waterproofing measures. These countermeasures have been proven to be effective and reliable, based on the successful operation of the Xi’an Metro for the past 3 years.