Key Techniques and Risk Management for the Application of the Pile-Beam-Arch (PBA) Excavation Method: A Case Study of the Zhongjie Subway Station

Table 3

Management critical value for settlement of ground surface and building.

Construction step	Surface settlement	Building settlements		Horizontal convergence	Crown settlement
		Absolute	Differential
Pilot heading excavation	80	25	—	10	50
Supporting arch	35	10	—	—	20
Main structure	25	5	—	15	—
Summation (mm)	140	40	0.002𝐿	15	70

𝐿 denotes the length of the existing building in the direction perpendicular to the tunnel axis.