Numerical analysis, design and behavior of rockfill dams with reinforced concrete faces during seismic actions

Introduction. Over the last 10–20 years many rockfill dams with reinforced concrete faces that are 140–200 m high (Mohale in Lesotho, Tian Sheng Yao, Zipingpu in China, etc.) have experienced serious problems, including face slab cracking and perimeter joint opening. Most of these dams were built in high seismic hazard areas, and their seismic resistance to the maximal earthquake exposure, having the magnitude equal to 8–9, raises doubts. The goal of this research is to employ numerical methods to verify the seismic resistance of dams, to project their behavior in case of the seismic exposure that may damage the dam face, cause the face joints to open and the dam face to detach from its toe, etc. Materials and methods. The author offers his analysis of reliability and applicability of numerical methods to the seismic resistance of dams. Incidents have demonstrated the need for a thorough assessment and analysis of each aspect of a new project whenever it is extrapolated from the precedent. Results. The analysis of the dam behavior in the course of the first reservoir filling has demonstrated face top cracking that causes its damage. Deeper in the water, face joints may be exposed to localized damages due to compression and shear; one should expect vertical face joints to open; excessive compressibility of the downstream rockfill zone may cause the water to leak through the dam face. The author offers recommendations for the performance of the dynamic analysis of dams in respect of the boundaries of the computational domain, given that seismic waves are transmitted or absorbed at the interface between the dam face and the transition zone, on the one hand, and between dam slabs, on the other hand. In furtherance of his recommendations, real and synthetic accelerograms are applied to the bottom boundary of the computational domain; the choice of an explicit or implicit computational method should be made; the author’s method pre-sets the intermediate solution which is to comply with the accelerogram digitization pattern. Conclusions. In addition to internationally established measures for improving the static and seismic safety of dams, the author proposes a new effective dam safety improvement method to be used in the course of designing high dams to be con-structed in high seismic hazard areas. This method improves dam safety by drastically reducing face deflections with the help of a support zone made of roller compacted concrete instead of the gravel transition zone, as exemplified by the 275 m high Kambaratinskaya-1 dam in Kyrgyzstan and the 192 m high Sogamoso dam in Colombia (both dams are located in highly seismic regions). The information on China's successful track record in designing and building similar dams, which are 220–250 m high, is also provided.