Mechanisms of Reservoir Impoundment-induced Large Deformation of the Guobu Slope at the Laxiwa Hydropower Station, China: Preliminary Insights from Remote Sensing and Numerical Modelling

The construction/operation of ultrahigh arch dams may impose significant perturbations to surrounding mountains, resulting in landslide motions of rock slopes and endangering the safety of hydropower systems and human habitats. For example, the Laxiwa Hydropower Station in China witnessed its nearby Guobu slope displacing significantly after the reservoir impoundment and having so far displaced up to ~40 m. It is of great importance to understand the mechanisms driving this large deformation. Here, we present some preliminary results from a combined remote sensing and numerical modelling investigation of this slope before, during, and after the reservoir impoundment. Analysis based on the differential interferometric synthetic aperture radar (DInSAR) data indicates that the slope had already been actively creeping at a rate of ~10 cm/year (e.g. in years of 2003-2005). We develop a geological model including different rock mass compartments and various discontinuity structures as well as a realistic representation of the suspended ancient landslide. We model the coupled hydro-mechanical and creep behaviour of the slope in response to reservoir impoundment. A good agreement is reached between the simulation results and field measurements of slope displacement time series recorded at different elevations of the slope surface. Our results show that the reservoir impoundment causes notable pressure changes at the toe region of the slope, leading to strong deformations (under coupled poroelastic and primary creep effects) that propagate upslope with the ancient landslide partially reactivated. These deformations tend to decelerate significantly after the impoundment due to the transition to secondary creeps.