Application of the Upper-Bench CD Method in Super Large-Span and Shallow Tunnel: A Case Study of Letuan Tunnel

Table 3

Safety evaluation of secondary lining.

Position	Maximum axis force (kN)	Maximum bending moment (kN·m)	Safety factor
B0	96.7	46.2	11.6
B1	106.6	18.5	7.2
B3	177.6	36.8	3.8
B4	173.4	−6.7	14.8
B5	139.4	9.1	12.7
B7	90.4	−37.4	10.4
B8	13.6	88.8	23.8
B9	225.4	−21.4	13.3
B10	250.2	−70.2	10.5
B11	255.2	−8.7	10