Behavior of rockfill dam under complex terrain condition

Abstract

The behavior of concrete face rockfill dam (CFRD) is more dependent on valley terrain than rockfill deformation. The objectives of this study are to research the influence of valley topography condition on the deformation and stress of a CFRD, especially with relevance to the behavior of face slab under complex terrain conditions. First, the research on the effect of valley shape factor on perimeter joint deformation used monitoring data with a combined total of 22 CFRDs from 8 countries. The results show that the perimeter joint deformation decreases nonlinearly with increasing valley shape factor A/H². A/H² = 2 ~ 4 or L/H = 2 ~ 5 can be considered an intervenient valley which contains both characteristics of the narrow and wide valley. Then, numerical analysis is applied to predict the behavior of Nam Ngum 2, a 182-m-high concrete face rockfill dam, during initial impoundment via a three-dimensional finite element analysis. A series of finite element analyses aimed at investigating the influence of the intervenient valley and complex topography condition which in turn depends on slope angle and angle mutant of the abutment on stress and deformation of concrete face slab on CFRD. All results indicate that the arch effect is crucial to deformation and stress of the CFRD in the intervenient scale of valley shape factor. Steeper slope and convex catastrophe point in abutment rapidly aggravate the tensile stress of the face slab and the deformation of the joints, which threaten the safety of the impervious system of CFRD. The hardening soil model is used in the nonlinear analysis for rockfill, and the results show that a good agreement between computed results and dam field monitoring data can be achieved.