Land subsidence-induced damage assessment along Beijing–Tianjin high-speed railway from space using high-resolution TerraSAR-X data

Beijing and Tianjin are two mega-cities in China having exhibited large land subsidence for decades, mainly due to groundwater over-exploitation, which is believed to have induced potential damages to man-made linear infrastructure such as the Beijing–Tianjin (Jingjin) high-speed railway. Spaceborne interferometric synthetic aperture radar (InSAR) has been widely employed to investigate land subsidence in cities in the world including Beijing and Tianjin. However, further research is required to evaluate the service limit state of the high-speed railway derived from high-resolution satellite displacement measurements. This is partly due to the stringent demands of high-speed railways and, more significantly, the absence of damage indices for identifying structural damage. In this paper, high-resolution TerraSAR-X data were used to examine land subsidence in Beijing Plain during the period from April 2010 to December 2019, revealing a maximum mean displacement rate of above 110 mm/year. Three damage indices, namely the slope gradient, the vertical radius of curvature, and the angular distortion, are proposed to identify potential damage in high-speed railways using InSAR-derived displacements. It turns out that the angular distortion is the most appropriate damage index, and areas with potential damage have been identified along the Jingjin high-speed railway, which is consistent with its maintenance records. It is believed that this proposed damage identification method, together with the increasing high-resolution InSAR observations, can be routinely applied to identify potential damages to high-speed railways, which will, in turn, guarantee their safe operation.