Ground subsidence risk mapping and assessment along Shanghai metro lines by PS-InSAR and LightGBM

Ground subsidence is a typical geological hazard in urban areas. It endangers the safety of infrastructures, such as subways. In this study, the ground subsidence risk of Shanghai metro lines was mapped and assessed. Firstly, PS-InSAR was used for the ground subsidence survey, and subsidence intensity was divided into five classes according to subsidence velocity. 10 subsidence causal factors were collected and the frequency ratio method was applied to analyze the correlation between subsidence and its causal factors. Then LightGBM model was used to generate a ground subsidence susceptibility map. And receiver operating characteristic curve and area under the curve (AUC) were adopted to assess the model. And AUC is 0.904, which suggests the model's performance is excellent. Finally, a risk matrix was introduced to consider the intensity and susceptibility of ground subsidence. The risk of ground subsidence was mapped and classified into five levels: R1 (very low), R2 (low), R3 (medium), R4 (high), and R5 (very high). The results showed that the risk of subway ground subsidence exhibited a regional-related characteristic. Metro lines located in areas with higher ground subsidence risk levels also had higher ground subsidence risk levels. Meanwhile, the statistical results of subway ground subsidence risk levels showed that subway stations were safer than sections.