Spatiotemporal evolution of surface deformation based on MT-InSAR and mechanism analysis along Zhengzhou Metro, China

Abstract

Subway construction is one of the effective means to boost economic and social development, as well as relieve urban traffic pressure. However, the surface deformation in the process of its operation and maintenance has become one of the most intractable problems faced by urban construction, planning and management departments. This study delved into the surface deformation evolution and underlying mechanisms along the subways in Zhengzhou, China. Leveraging a dataset comprising 88 Sentinel-1A ascending orbit images, we applied a hybrid approach of PS-InSAR and SBAS-InSAR inversion methods to extract both the temporal deformation field and deformation velocity field within the study area. The study interpreted the spatiotemporal evolution of surface deformation within the metro corridor buffer zones. Additionally, through the integration of well-logging hydrological data and geological borehole data, we comprehensively elucidated the mechanisms driving surface uplift in Zhengzhou central urban area. With the intention of accurately analyzing the evolution over two settlement funnels, we implemented a Bayesian estimation algorithm to denoise the subsidence curves extracted from MT-InSAR deformation field at the Shamen metro station. Then, the subsidence velocity features for the subsidence troughs were analyzed at this station. According to the theory of effective stress, the calculation model of soil element consolidation compression was established, and the methodology calculating soil strata compression within the water-level drop funnel was proposed. Based on the measurement data, the reliability of the proposed calculation model and methodology was verified, and the mechanism of surface settlement in typical subway station is revealed. The results demonstrated that significant subsidence zones along the metro corridor predominantly cluster in the eastern, northwestern, and southwestern sectors of the central urban area. Notably, the most substantial subsidence occurs in the Huiji District (Line 2) to the northwest and the Jinshui District (Lines 1 and 5) to the east, with maximum subsidence rates of 16 mm/a and 12 mm/a, respectively. Conversely, uplift areas are primarily situated at the convergence of four administrative districts (Erqi District, Zhongyuan District, Jinshui District, and Guancheng District), affecting Lines 1, 2, and 5 of the metro, with a peak uplift of 67 mm. This uplift area closely aligns with the underground water prohibitive extraction zone. Prior to groundwater prohibitive extraction, it indicated seasonal fluctuations for underground water level, which subsequently exhibited a notable rise following conservation measures. There exists a growing dose feedback function relationship between surface uplift and well-logging level in the prohibitive water-extraction zone. The root mean square error (RMSE) and relative root mean square error (RRMSE) are ±3 mm and 6.7 %, respectively. The theoretical calculation values afford a better fit with the measured values, which approves the effectiveness of the proposed calculation model. The principal reason behind the dual subsidence funnels observed on the surface at the Shamen metro station, Zhengzhou China is attributed to groundwater discharge during metro operation, with the subsidence rate at the maximum point conforming to a Logistic time function curve. The insights gained from this study hold practical significance for not only mitigating potential risks but safeguarding urban public security in the process of subway operation.