Comprehensive Deformation Monitoring and Characteristic Analysis of Ancient Landslide Reactivation Induced by Tunnel Construction

Identifying the deformation characteristics of an ancient landslide induced by tunnel excavation is crucial for revealing the tunnel-landslide interaction mechanism. In this study, a ancient landslide reactivated by a highway tunnel excavation in a mountainous region of Southwest China was taken as a case study. Based on field investigation, the deformation characteristics of the reactivated landslide were systematically analyzed by integrating numerical simulation, Distributed Scatterer Interferometric Synthetic Aperture Radar (DS-InSAR) time-series monitoring, and in-situ surface monitoring techniques. The results indicate that: (1) Spatially, the landslide body exhibits significant zonation. The deformation is mainly concentrated in the area of Landslide Zone I above the tunnel, where surface displacement shows a decreasing trend from top to bottom, while the displacement in ZoneⅡ remains relatively stable. (2) In terms of temporal evolution, the landslide deformation undergoes stages of "slow creep - accelerated deformation - local reactivation" . Specifically, from July to October 2015, the displacement of the slope body above the right tunnel exhibits a distinct trend of accelerated deformation. (3) The results from numerical simulation, InSAR interpretation, and in-situ monitoring are highly consistent regarding deformation trends. The unloading effect caused by tunnel excavation is identified as the direct cause for the reactivation of the ancient landslide.