Experimental study of reservoir bank collapse in gravel soil under different slope gradients and water levels

Abstract

Reservoir bank collapse is a common hydrogeological problem in mountainous areas in the southwest region of China. This paper presents an experimental study to investigate the mechanisms and characteristics of the bank collapse problem in gravel soil, replicating the conditions of the Pubugou reservoir in Sichuan Province of China. A laboratory model was set up to monitor the hydrological responses and deformation development of the bank slopes under different slope gradients (i.e., 30°, 35° and 40°) and water level conditions (i.e., constant water level and fluctuating water level). The innovative setup enabled real-time monitoring of moisture content, pore-water pressure and deformation of the slope with the consideration of wave scouring effect. Results showed that the increase in the slope gradient would not only increase the slope mass sliding force, but also shorten the infiltration distance, making the slope more prone to saturation. The fluctuation in water level would destabilize the bank slope by deteriorating both the physical and mechanical properties of the soil, generating hydrodynamic pressure with the water level drawdown, and expanding the localized collapses to form a larger scale failure. The overall bank collapse mechanism can be divided into three stages: (1) partial collapse stage, (2) expansion and development stage, and (3) final stabilization stage. A new empirical equation was proposed to correlate the slope gradient, slope height, and coefficient of permeability with the bank collapse width in gravel soil.