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

Table 9

Assessment results.

Item	Fuzzy composite evaluation	Risk evaluation by BPNN
Single risk item	Vault settlement, ground settlement, and leakage	Vault settlement, ground settlement, and leakage
Combined risk items	Landslides and water seepage	Landslides and water seepage
Risk-indicator value	RA = 78%; RB = 73%	RA = 81%; RB = 73%
Risk level	High risk	High risk
Countermeasures	Adjust the spacing of tunnel excavation for double lines to reduce disturbance; improve the intensity level of synchronous slurry; carry out double-liquid grouting after synchronous grouting; increase grouting pressure and soil bin pressure appropriately to control sedimentation; reduce digging speed; carry out stratum reinforcement; monitor in real time and adjust grouting parameters in time