Review of Seepage Behaviour on Concrete Facing Rockfill Dam Based on FEM Simulation and Chemical Aspect

Concrete Facing Rockfill Dam (CFRD) is a popular type of dam for hydropower plant due to its relatively good stability than others. However, CFRD have a potential technical issue concerning seepage and leakage as it has a thin impermeable layer. In this study, dam stability against seepage was evaluated by finite element simulation. Concrete facing layer and dam foundation were assumed to undergo permeability coefficient (K) increasing within 3 stages and would be simulated within 15 scenarios. Furthermore, seepage chemistry analysis was conducted to evaluate seepage water interaction with the dam foundation. FEM simulation shows that increasing of permeability coefficient on concrete facing < 10^-5 m/second tends to cause the exceedance of allowable seepage discharge (q-_simulation > q-_allowable). On other hand, the increase of permeability coefficient on the dam foundation tends to cause the dam failure against seepage force. According to seepage chemistry analysis, calcium ion Ca²⁺ concentration increase 1.8 times from 13.6 meq/L on 2019 sampling to 24.8 meq/L on 2020 sampling. The seepage chemistry analysis shows the sign of carbonate rock interaction as dam foundation with seepage water.