Research on Ground Settlement Regularity of Soft Rock Tunnel under Ultrasmall Distance

Table 3

Comparison of surface settlement values caused by each process.

The excavation phase	Pipe-shed small conduit combination reinforcement (mm)	Advance grouting reinforcement of small conduit (mm)	Unreinforced (mm)
Annular excavation	−6.1	−13.4	−18.9
Core excavation	−4.2	−6.4	−6.8
Lower step excavation	−1.8	−4	−4.9
Excavation causes cumulative settlement	−12.1	−23.8	−30.6