Solution to 3-D unsteady saturated-unsaturated seepage problem and accurate treatment of saturated and unsaturated exit surfaces of seepage

A numerical procedure for finite element method solution to 3-D steady and unsteady,saturated unsaturated seepage problems is thoroughly presented in the paper.At the same time among the descriptions of the seepage boundary condidons,the correct mathematical expression of the unsteady exit surface of seepage is also established.In order theoretically accurately to describe the conditions of the unsaturated exit surfaces and to develop a strict numerical technique for simulating them,two new definitions of extreme moisture content and coefficient of water evaporation on unsaturated exit surface are originally given on the basis of the natural coherent physical properties of seepage media.Since the exact locations of the seepage exit lines between the saturated and unsaturated seepage areas couldn't be known at the beginning,a new solution concept and procedure are proposed.They use the transformation of the boundary condition types of the saturated and unsaturated exit sur faces during the numerical iterations according to the middle solutions to the problem.The location of the exit line of seepage can accurately be identified and the two-type exit surfaces be treated in detail.Therefore,the thought of accurate numerical treatment of saturated and unsaturated exit surfaces is implemented for the first time.Theoretically the problems of steadyunstea即and saturated-unsaturated seepage fields are solved thoroughly and rigorously.