Research on Coupling Degree Model of Safety Risk System for Tunnel Construction in Subway Shield Zone

Table 2

Risk assessment system for subway shield tunnel construction.

	The 1st-level indicators	The 2nd-level indicators
Risk factors	Human risk factors R1	Physiological factors R11
		Mental factors R12
		Technical factors R13
	Machinery risk factors R2	Improper installation R21
		Mechanical failure R22
		Machine breakdown R23
	Environment risk factors R3	Natural environment factors R31
		Working environment factors R32
		Social environment factors R33
	Management risk factors R4	Management mechanism factors R41
		Management organization factors R42
		Safety management system R43