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

Table 4

Calculation of the unsupported span.

Tunnel excavation method	Literature [15]	Literature [16]	This paper (m)	On-site
CRD	Unrestricted	K < 4.6	4.8	3～5 m
Bench cut method	2 m	K < 2.9	1.2	1～1.5 m