Hydraulic response and stability of a reservoir slope with landslide potential under the combined effect of rainfall and water level fluctuation

Abstract

The Xinhua slope of Dagangshan Reservoir is taken as an example to study the potential for reservoir landslides under the combined effects of rainfall and water level fluctuations. Through field investigation, monitoring analysis by global navigation satellite system and numerical simulation, the hydraulic response and stability of the accumulated deposits on the Xinhua slope were evaluated. Three occurrences of large deformations were recorded by real-time monitoring. By comparing the deformation records with the hydrological records, it was found that the first one was caused by water storage, and the last two were due to the coupling effect of rainfall and water level drawdown. Deformation of the reservoir overburden cannot simply be thought of as the sliding of a single block (geology survey showed deep sliding surfaces with depths of 50–70 m), but shallow sliding (less than 5 m) is also much likely to occur revealed by a supporting evidence from deformation records. In cases where hydrostatic pressure and transient osmotic forces are favorable for shear resistance, softening may play a major role in the process of impoundment leading to deformation. The deformation pattern of the slope deposits changes as it enters operation. A drawdown of water level during flood season accelerates the deformation, while a following rise of water level inhibits this acceleration. More extensive monitoring (i.e. pore water pressure sensor and inclinometer) and more in-depth analysis are needed in the future, and this article is a synthesis of limit equilibrium and infinite slope analysis to better understand the deformation patterns and response mechanisms of reservoir accumulation.