Unconfined seepage analysis with composite element method

Based on the method of adjusting the conductivity matrix, the composite element method is proposed to deal with the elements intersected by free surface in the analysis of unconfined seepage problems. Each composite element has two sets of the nodal hydraulic potential, one is used to interpolate the hydraulic potential in the saturated domain, another used in the domain above free surface. According to the variational principle, the governing equation is derived and is implemented in the program. With the composite element method, the problem of interpolation on free surface is well solved and the impact of the domain above free surface upon the hydraulic potential in the saturated domain is avoided. Moreover, the outflow boundary can be treated in the calculation more conveniently and more accurately. The effectiveness of the method is verified by the numerical example.