Predictive Analysis of Settlement Risk in Tunnel Construction: A Bow-Tie-Bayesian Network Approach

Table 9

Details of bow-tie components in Figure 9.

Event	Symbol	Logic link type	Failure model
Ground settlement	Excessive surface settlement	OR gate	—
Catastrophic geology	M1	OR gate	—
Unforeseeable factors	M2	OR gate	—
Excavation parameters	M3	AND gate	—
Confined water	X1	—	Environmental failure
Ground cavity or flow sand	X2	—	Environmental failure
Obstacles	X3	—	Environmental failure
Segment damage	X4	—	Operational error
Abnormal TBM shutdown	X5	—	Multiple failure
Seal failure at shield tail	X6	—	Multiple failure
Excessive deviation from axis	X7	—	Operational error
Equipment failure	X8	—	Multiple failure
Untimely grouting	X9	—	Facility failure
Excessive cutter head torque	X10	—	Facility failure
Improper control of face pressure	X11	—	Facility failure
Excessive thrust	X12	—	Facility failure
Improper control of excavation speed	X13	—	Facility failure
TBM shutdown	CE1	—	Multiple failure
Grouting in settlement area	CE2	—	Multiple failure
Bentonite injection to soil chamber and TBM shield	CE3	—	Multiple failure