This study investigated the transient seepage of an earth dam during reservoir impounding through numerical modeling and back-calculated the dam’s permeability coefficient. Additionally, the potential trend of decreasing natural vibration frequency with increasing water level in the reservoir was explored through a comparative evaluation of the numerical results against field-measured vibration signals. The FLAC2D finite difference code was used to conduct the numerical simulations; the reservoir filling process was modeled in a staged manner by incrementally
increasing the water level. The natural vibration frequency of the dam was identified using a combination of preliminary frequency sweep techniques and detailed resonance calculation methods.The water levels and vibration signals of the dam were measured during a large-scale double breach field test, and the results were systematically compared with those obtained from the numerical simulations. Through back-calculation,the permeability coefficient of the earth dam was estimated to be 0.008 m/s. The results also confirmed that the natural vibration frequency of the dam decreased as the reservoir water level increased, a trend consistent with the changes in vibration frequency observed during field monitoring.
Key Words: dam breach, transient seepage, vibration frequency, FLAC2D, back-calculation