Structural Monitoring of Metro Infrastructure during Shield Tunneling Construction

Table 2

Alarming indices for construction monitoring of shield tunneling.

Item	Alarming index
	Daily variation	Design value	Warning value
Deformation of adjacent underground colligation pipelines	2 mm	20 mm	80% of design value
Settlement of adjacent ground surface	3 mm	+10 mm/−30 mm
Vertical displacement of surrounding buildings	2 mm	20 mm
Settlement of tunnel	2 mm	20 mm
Tunnel clearance convergence	2 mm	30 mm