Abutment stability assessment of the Hongrin arch dam using 3D distinct element method

The Hongrin north dam is a double curvature concrete arch dam located in western Swiss Prealps, which attains 125m high. The right bank abutment of the dam mainly consists of intensively jointed Neocomian limestone and exhibits zones of potential instability. At the time of construction (1965-1969), this slope was reinforced with rock anchors. Subsequent hydrogeological study and groundwater monitoring revealed the presence of water pressure due to a slight seepage flow through the rock joints in the dam foundation. This latter evidence raised an additional concern about the stability of the abutment. In a dedicated study, the stability of the right abutment the Hongrin north dam abutment has been assessed using continuumdiscontinuum numerical analysis. 3DEC (3-Dimensional Distinct Element Code) has been used to model the complicated slope geometry and to explore the role of rock discontinuity in the failure mechanisms. The rock mass is defined as deformable distinct blocks which interact along frictional discrete discontinuities representing the rock joint sets. The water pressure is introduced as fluid pressure boundary condition along the discontinuities, and the rock reinforcement is modeled as structural elements working across the discontinuities. The dam reaction forces, derived from a separate finite element analysis, are evaluated for their possible effects on the stability. The model examines the sensitivity of the abutment stability to the presence of joint water pressure and evaluates the improving effects of rock reinforcement. The results of the analysis allow achieving an enhanced understanding of potential failure mechanisms and helps in proposing further suitable measures to improve the stability of the abutment.