Surface deformation monitoring of subway before and during construction based on PS-InSAR

The construction of urban subways induces ground surface deformation, and regional surface deformations harm subway construction. Measuring the surface deformation of the project area before and during construction is necessary. The construction of the Tianjin Metro Line 6 Lushuidao Station–Shuanggang Station section was used as the study case. A total of 6028 permanent scatterers (PSs) in 2.5 km² of the project area were detected using persistent scatterer interferometric synthetic aperture radar (PS-InSAR). The distribution of PSs, the regional surface deformation rate around the station and along the tunnel, and the time-series deformation of individual PSs were analyzed. Results show that the PSs are mainly distributed on buildings. Few PSs are distributed on roads and natural ground surface, and almost no PSs are found on vegetation-covered and river areas. PS-InSAR deformation monitoring accuracy could achieve millimeter level. Moreover, the ground around Lushuidao Station is more stable than that around Shuanggang Station. Before the construction, the maximum settlement occurred on building 12 with a value of 13.98 mm, and the maximum lifting occurred on building 17 with a value of 15.85 mm. Finally, building 4 and ground on the east side adjacent to buildings 12 and 13 were affected by the construction of the pit. The PSs on them showed a significant settlement trend after the excavation.