###### Abstract  
While the construction and operation of subways have brought convenience to commuters, it has also caused ground subsidence and cracks of facilities around subways. The industry mainly adopts traditional manual detection methods to monitor these settlements and cracks. The current approaches have difficulties in achieving all-weather, all-region dynamic monitoring, increasing the traffic burden of the city during the monitoring work. The study aims to provide a large-scale settlement detection approach based on PS-InSAR for the monitoring of subway facilities. Meanwhile, this paper proposes a crack detection method that is based on UAVs and the VGG16 algorithm to quantify the length and width of cracks. The experimental data of Shenzhen University Section of Metro Line 9 are used to verify the proposed settlement model and to illustrate the monitoring process. The developed model is innovative in that it can monitor the settlement of large-scale facilities around the subway with high accuracy around the clock and automatically identify and quantify the cracks in the settled facilities around the subway.  
subway subsidence monitoring; PS-InSAR; VGG16; digital image processing +
Footnote †: journal: Applied sciences  
the safety of engineering facilities along the subway lines stand out, along with the concerns surrounding subway construction and operation. The problems of land subsidence caused by subway construction have received extensive attention from scholars and governmental departments in many cities [8], such as Florence [9], Tokyo [8], Beijing [10], Hong Kong [11], and Shanghai [12]. The traditional methods have certain limitations, such as the lack of accurate and continuous characterization records of subway facilities; the difficulties of inspecting the hidden places of engineering facilities; the road sections need be closed for the inspection, which increases the traffic burden of the city; and the significant subjectivity and difference in the records among inspectors [13]. In order to ensure the safety of residents' lives and property, it is urgent to establish new methods to monitor the health of engineering facilities along the subway lines.  
Settlement screening and appearance inspection are two primary engineering facility monitoring methods [14; 15]. PS-InSAR technology (Persistent Scatterer Interferometric Synthetic Aperture Radar technology) can provide millimeter-level motion information with superior performance, which can monitor abnormal behavior in a short period and motion information that cannot be found visually [16; 17]. Therefore, PS-InSAR technology is extensively used in the settlement monitoring of infrastructure, including buildings [18], motorways [19], airports [20], subways [5], etc. For instance, [PERSON] et al. [21] used PS-InSAR technology to analyze ground fissures and the land subsidence of Beijing Capital International Airport and found active ground fissures. In addition, based on PS-InSAR technology, [PERSON] et al. [22] carried out long-term ground deformation monitoring and modeling of the Guangzhou metro networks. These methods, however, have certain shortcomings, i.e., although PS-InSAR technology can quickly and accurately obtain the settlement data of engineering facilities around the subway, it cannot capture intuitive crack images. Furthermore, traditional crack recognition and measurement methods are not able to accurately identify and measure cracks in facilities around the subway due to the complexity of the environment around the subway and the diversity of structures and materials. To overcome the limitations of the current methods, a method integrating PS-InSAR, UAVs and the VGG16 algorithm was developed to monitor the settlement along the subway, inspect the appearance of facilities around the subway, and identify and quantify cracks, which improves the accuracy and speed and reduces the cost of the monitoring of settlement and cracks for engineering facilities around subways.