Integration of Multiband InSAR and Leveling Measurements for Analyzing the Surface Subsidence of Shield Tunneling at Beijing-Zhangzhou High-Speed Railway

Table 1

The feasibility of the leveling and InSAR methods for deriving the various subsidence-related parameters [21–23].

Subsidence-related parameters	Description	Measurement requirement	Suitable monitoring techniques	Effect
Angle of advance influence in longitudinal section	When the gob has reached the critical size, or nearly so, on the major cross-section of a movement basin, the critical line at the faceline and the line connecting the movement initiation point on the surface with the faceline is the angle of advance influence	High precision; Frequent monitoring and real-time monitoring	Leveling	Determine the influence range of ground subsidence when the working face advances to any position in the process of advancing on the working surface
Lag distance of maximum subsidence rate	The distance between the maximum subsidence velocity point and the position of the working surface	High precision; Real-time monitoring	Leveling	The point where the surface has the highest subsidence velocity is the place where the surface moves most violently at that time.; Knowing the law of the lag angle, we can determine the area with the most violent ground movement at any time during the advancement of the working face
Lag angle of maximum subsidence rate	The angle between the line connecting the point with maximum subsidence velocity and the working face	High precision; Real-time monitoring	Leveling
Boundary of subsidence in transverse direction	The contour line of 2 mm of subsidence is used to define the edge of the surface movement	Medium precision; Large area	Leveling and InSAR (C-band)	It is of great significance for controlling ground subsidence and protecting buildings by monitoring the ground surface and the sinking of ground building
Far field displacement	The far field displacement from the shield tunnel is usually small with long settlement time. This type of subsidence is usually far away from the tunnel	High precision; Large area	InSAR (X-band)
Subsidence duration, etc.	The time it takes for the ground surface to become stable at the maximum subsidence point	Relatively short monitoring time (6 days); Real-time monitoring; Small area	Leveling	Determining the time range of drastic changes in the surface of the shield tunnel is of practical significance for the protection of the upper surface of the shield tunnel and the building