关键词: 二元结构堤基, 堤内压盖, 虚单元固定网格法, 2次入渗, 空气单元, 临界破坏点

Abstract:

A covering soil layer model in binary levee foundation was established according to the geology characteristics of levee foundation in the Dongting Lake region. A seepage finite element program was developed based on seepage FEM and imaginary elements fixed mesh method. The second infiltration problem in the seepage analysis was solved through increasing a lot of strong permeability air elements on top of covering soil layer. The influence of covering soil layer width on the anti-seepage effect was analyzed, and the influence curves of covering soil layer width on the maximal seepage gradient inside levee were gained under the two cases, with and without pond inside levee, then the critical failure point method was put forward based on the features that the influence curves mainly changed linearly. The critical failure point method can be used to determine the critical width of covering soil layer, and it is defined as follows: the intersection point between the extending influence curve and the allowable seepage gradient of covering strata is called critical failure point; and the left region of critical failure point is danger and needs to cover; whereas the right region is safe and needs not to solve. The application of critical failure point method reduces the size of finite element model to a great extent, avoids repeating finite element calculations and improves the calculation efficiency evidently, compared with the traditional methods including Code for design of levee project and finite difference method, the critical failure point method is preponderant obviously.

Key words: binary foundation, covering soil layer inside levee, imaginary elements fixed mesh method, second infiltration, air element, critical failure point