The Influence of Constitutive model for Rockfill Material on the Calculated Stress and Deformation of Concrete-Faced Dam

Choice of constitutive model for rockfill materials is the most influencing factor that affects the computed stress and deformation results of concrete-faced dams (CFD). In this paper, Duncan’s E-B (EB) nonlinear elastic model and Nanshui (NS) double yield surface elastoplastic model were used for rockfill materials to simulate, by three-dimensional finite element method, the construction and impounding processes of a typical CFD. The differences in the displacement and stress of rockfill zones and concrete slabs were compared and the reasons were analyzed. We found two most important differences. First, displacement quantities such as the dam settlement and slab deflection predicted by NS model are smaller than those obtained by EB model, and this difference can be attributed to the higher minor principal stresses and therefore higher deformation moduli within rockfill zones by the former. Second, EB model predicts a tensile zone along the upstream slope near the bottom of face slabs, while results by NS model show that the slope stresses of face slabs are completely compressive. The tensile stress predicted by EB model is due to its isotropic elasticity nature, i.e., cushion materials expand along the slope under the huge hydrostatic pressure, leading to a displacement upward towards the dam crest. NS model, on the other hand, predicts an additional plastic volume contraction within the upstream rockfill zones due to the expansion of F1 yield surface, which completely counteracts the elastic expansion along the slope and results in a downward displacement of the cushion layer.