Protective Measures for a Tunnel on Xi’an Metro Line 6 Crossing Ground Fissure Zone

Abstract

Objective Xi’an Metro Line 6 Phase Ⅱ project encounters seven ground fissures along one of its tunnels, the poor engineering properties may cause partial tunnel collapse and uneven settlement at the base, exacerbating ground fissure activities and posing serious threats to the construction and operation of urban rail transit. Therefore, it is essential to study protective measures for this Line 6 tunnel crossing ground fissure zones. Method Based on the historical activity characteristics of the ground fissures intersecting Xi’an Metro Line 6 Phase Ⅱ project, a qualitative evaluation of the impact levels of each fissure on metro is conducted. Combining this qualitative evaluation results with the spatial relationship between the tunnel and the fissures, as well as the design value of recommended maximum vertical displacement for the fissures during a 100-year service life, estimates are made for the vertical, horizontal and axial displacements of the fissures and the longitudinal protective length of tunnel structure. According to the engineering prevention principles for Class Ⅱ ground fissure sites, corresponding protective measures are proposed for the tunnel crossing fissure zones. Result & Conclusion The protective measures for a Xi’an Metro Line 6 tunnel crossing ground fissure zones include: adopting segmental seams for tunnel lining structure, increasing tunnel cross-sectional clearance, reinforcing local linings, and using flexible joints at the seams. These protective measures successfully ensure the safe construction and operation of seven metro lines.

Keywords

• urban rail transit
• tunnel
• ground fissure
• protective measure