Abstract: When a concentrated leakage passage exists in the body of a dam, the passage will exchange water with its surrounding porous media driven by pressure difference. Such exchange may lead to an increase in dam discharge, but it is often ignored in traditional seepage field analysis. This study develops a sand tank model to simulate the presence of concentrated seepage channels in a dam, and examines the mechanism of water exchange and the water discharges from the concentrated leakage passage and the porous medium. A new formula for calculating the water exchange coefficient is then suggested. Results show that the amount of water exchange is proportional to passage diameter (D), porous medium permeability coefficient (Km), and hydraulic gradient (J). Orthogonal tests are adopted to analyze the influence degree of each factor on the water exchange capacity, revealing D is most influential, followed by J and Km. The results demonstrate the importance of the channel-medium exchange in seepage calculation, and would lay a basis for seepage field analysis of concentrated seepage channels in the dam.

Key words: dam leakage, concentrated leakage passage, water exchange, sand tank test, orthogonal test