Risk Assessment System Based on Fuzzy Composite Evaluation and a Backpropagation Neural Network for a Shield Tunnel Crossing under a River

Table 4

Numerical simulation approach to risk factors.

Risk factor(s)	Simulation method
Level of the surrounding rock	Adjust physical parameters of soil
Depth of tunnel; depth of water coverage	Adjust overburden thickness and water pressure above the tunnel
Excavation method	Adjust excavation sequence and pacing
Strength of synchronized slurries	Adjust physical parameters of shell units
Strength of secondary grouting	Adjust physical parameters of line units
Grouting pressure	Apply surface forces along the tunnel perimeter
Soil bin pressure	Apply thrust force on excavation face