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

Table 2

Stability of tunnel face and vault under different unsupported span.

The unsupported span	2.0 m	3.0 m	4.5 m	5 m
State description	The tunnel face is stable, with a small amount of slump	The arch crown collapsed and the tunnel face began to break	Both the arch crown and the face failed	The arch crown and the face entirely are destroyed