| Based on the previous research findings in hydraulic engineering, the basic theories on caculating the unsteady seepage field with finited element method (FEM) are studied in this paper. The key contents involved are as follows:(1)Based on the theory of variation, the FEM form of seepage calculation is concluded by using interpolation function and isoparametric transformation, and the mathematical model of unsteady seepage is established. The solution stability of the FEM matrix is studied, and the symmteric successive over relaxation-precondition conjugate gradient method (SSOR-PCG) to solve the large-scale FEM equations is recommended.(2)After the several methods to solve this problem have been analyzed, the key issue in solving unsteady seepage problem is to identify the location of free table and outflow line. The nodal virtual flux method is used to solve the seepage problem with free table, and the validity of the method is proved by an example.(3)The approximate method is proposed by changing the surface integral to plane integral, because it is difficult to correctly deal with the integral about the free table. A program for solving the unsteady seepage field is written, and it is proved to be correct by an example.(4)As a effective method on seeking the reasonable result in complete region, the genetic algorithm (GA) could be a important tool in seepage conter-analysis, after being improved its partial search ability. A program for the seepage conter-analysis is written, based on the improved accelerating genetic algorithm (IAGA), combined with the program of solving the unsteady seepage field, and it is validated by a example.(5)The primary factors about the abnormal phenomenon of seepage in Zhangshan Lock are summed up as a series of characteristic parameter variable. The causes which bring the abnormal phenomenon are made clear by conter-analysis, seepage analysis and contrast analysis, and then some economical reliable processing measures are proposed.
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