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

Table 2

Safety evaluation of initial support.

Position	Maximum axis force (kN)	Maximum bending moment (kN·m)	Compressive safety factor		Tensile safety factor
			Minimum value	Stability value	Minimum value	Stability value
B0	1935	3.3	1.3	3.9	1.36	4.27
B1	1751	−3.6	1.51	2.18	1.43	2.04
B2	141	0.9	19.8	93.9	16.8	70.7
B3	1849	8.7	1.31	2.07	1.48	2.35
B4	1473	6.1	1.65	4.14	1.85	5.9
B5	1812	4.6	1.37	7.28	1.47	15.5
B6	1708	1	1.48	2.49	1.51	2.62
B7	1967.3	5.4	1.26	1.69	1.36	1.78
B9	63.7	−11.7	27.2	9.27	11.6	6.4
B10	303	−8.4	13.6	34.5	6.2	154.8
B11	576	1.6	4.3	25	4.64	16.4