Evaluation of valley topography effects on the seismic stability of earth-rockfill dams via a modified valley topography coefficient

Abstract

This paper presents the impact of valley topography on the stability of an earth-rockfill dam slope during earthquakes. The valley site is simplified as an ideal trapezium. A series of three-dimensional numerical models with different valley floor widths and valley wall slopes are used to represent different geometries of the valley topography. A modified dimensionless valley topography coefficient ς is proposed to describe the shape characteristics of the valley topography quantitatively. Considering the most commonly used parameter, the length-height ratio of the dam (L/H), ς replaces L with the length of the median line, Lm, and introduces a shape index, S, as a correction factor on the basis of Lm/H. Comparing to L/H, data from previous studies indicate that ς has a better correlation with the increment ratio of FoS3D to FoS2D. The shear strength reduction technique and the pseudo-static approach are adopted to calculate the factor of safety and the associated critical slip surface of the dam slopes. The results show that the valley topography plays a positive role in the seismic stability of the dam in the cases investigated in this study, especially for narrow valleys and that the valley topography effect will decrease with increasing earthquake intensity.