Risk Assessment of an Existing Metro Tunnel in Close Proximity to New Shield Tunnels following Construction

Table 4

Risk grade classification table of existing tunnel structure.

Risk grade	Security status	Structural state of the existing tunnel
I	Unsafe	The structural deformation of the existing tunnel exceeds the deformation control standards and is considered serious; therefore, the metro cannot operate normally.
II	Relatively unsafe	The degree of structural deformation of the existing tunnel is large and exceeds the prewarning value of deformation. The tunnel structure should be comprehensively monitored and the metro should be operated slowly or at a limited speed.
III	Relatively safe	The structural deformation of the existing tunnel is normal, but there are certain factors that have a great influence on the structural deformation. It is necessary to monitor the structural deformation, and the metro can operate normally.
IV	Safe	Tunnel structure deformation is normal and the metro can operate normally.