Abstract: According to the principle of the air element method, which is used to model drainage holes in seepage analysis, a layer of air elements with higher permeability is attached to any possible overflow boundary in the seepage field, and these air elements are included along with the entity elements in a common finite element analysis of seepage, so that the overflow boundary can be automatically solved. The proposed method can not only avoid the numerical iteration in calculating the overflow boundary as in current methods, but also resolve the issues related to the inefficiency and divergence associated with the inaccurate positioning of overflow boundary. The numerical examples indicate that the calculation accuracy of the air element method is correlated with the permeability of air element but independent of its thickness. Once if the relevant parameters are well selected, the proposed method can precisely approach the current ones. Furthermore, the interface film element is introduced into the air element method in order to improve the poor imitation occurring at the contact surface between strong and weak permeable media. Finally, the application of seepage calculation in Xiaowan dam section #22 demonstrates the validity and applicability of the proposed method.

Key words: seepage, overflow boundary, air element method, drainage hole, interface film element