Abstract: Expansive soil can damage the civil engineering structures due to the swelling-shrinking characteristic when they are exposed to the water. Middle Route Project of the South-to-North Water Diversion is an important project for alleviating water shortages and optimizing water resource allocation in the North China Plain. One third of water channel in the Middle Route passes through the expansive soil region, threatening the safety of the South-to-North Water Diversion Project. It is urgent to monitor the ground deformation of expansive soil slope so that better understanding its engineering stability. In this context, 112 Sentinel-1A synthetic aperture radar (SAR) images with ascending orbit were processed by multi-temporal interferometric SAR (InSAR) technique to observe the time series deformation along the South-to-North Water Diversion Project. Meanwhile, the singular spectrum analysis (SSA) technique was used to decompose the time series deformation to analyze the deformation characteristics. The uplift deformation was observed in the excavating expansive soil slope, where the maximum deformation rate was 18 mm/a. This uplift deformation was mainly due to the soil unloading and rebound. In the filling region, the subsidence was observed due to the soil consolidation and the maximum subsiding rate was 15 mm/a. The magnitude of ground deformation was correlated with the excavating and filling thickness:the deeper excavation means the greater uplift, and the higher filling means the greater subsidence. The precipitation and temperature, which can cause the deformation temporal delay of 2~3 months, are two main external contributor to the expansive soil slope. This study will provide the evidence to the stability assessment of expansive soil slope along the South-to-North Water Diversion Project.

Key words: expansive soil, ground deformation, InSAR, SSA, the South-to-North Water Diversion