A Theoretical Calculation Method of the Unsupported Span for the Shallow Tunnel in the Soft Stratum

Table 1

and value of all grade of surrounding rock (China’s Code for Design of Railway Tunnels).

Grade	I	II	III	IV	V	VI
(°)	0.9	0.9	0.9	(0.7–0.9)	(0.5–0.7)	(0.3–0.5)
(°)	>78	70∼78	60∼70	50∼60	40∼50	30∼40