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

Table 3

The quantification of the risk level.

Risk level	I	II	III	IV
Security status	Unsafe	Relatively unsafe	Relatively safe	Safe
Quantitative values	1 ≤  < 1.5	1.5 ≤  < 2.5	2.5 ≤  < 3.5	3.5 ≤  < 4