Rapid Detection of Deformation Anomalies along the China–Laos Railway Using InSAR Phase Gradient Stacking

Abstract

The Kunming–Mohan section of the China–Laos Railway traverses complex mountainous terrain, making the rapid identification of deformation-prone areas essential for long-term operational safety. This study applied phase gradient stacking (PGS) to 200 wrapped differential interferograms generated under small-baseline criteria to detect deformation-gradient anomalies within a 10-km railway buffer. A normalized phase gradient index (PGI) was derived and jointly interpreted with time-series interferometric synthetic aperture radar (InSAR) displacements, digital elevation model–derived slope, and high-resolution optical imagery. The results show a low overall deformation-gradient intensity along the corridor, with a mean PGI of 0.08. Elevated PGI values are concentrated mainly in the central–northern corridor, particularly in Yuxi, which accounts for 54.9% of the strong-anomaly area. The PGS results are spatially consistent with time-series InSAR measurements in representative deformation zones. Infrastructure-scale analysis identified notable anomalies at Yanhe Station, the tunnel–bridge transition adjacent to the Babianjiang Bridge, and several tunnel portals. Multi-source interpretation further delineated 89 potentially unstable slopes, including 41 in Yuxi and 28 in Pu’er. Among them, 37 were attributed to natural slope evolution, while 26 were associated with engineering disturbance and 26 with reservoir infiltration. The results support PGS as an efficient, phase-unwrapping-free approach for first-pass screening of deformation-prone sections and prioritizing potentially unstable slopes along long mountainous railway corridors