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

Table 6

Quantification of risk factors.

Quantified value	x1	x2 (m)	x3 (m)	x4 (m)	x5 (MPa)	x6 (MPa)	x7 (MPa)	x8 (MPa)
0.2	VI	20	5	0	0	0	0.2	0.2
0.6	V	30	10	10	2	5	0.4	0.4
0.8	IV	40	20	20	4	10	0.6	0.6
1.0	III	50	30	30	6	15	0.8	0.8

Note. x₁–x₈ are the grade of surrounding rock, depth of burial, depth of cover, excavation interval, synchronous slurry strength, secondary slurry strength, grouting pressure, and soil bin pressure, respectively.