Abstract: In an urban regional seepage field, thousands of gaps between building foundations make finite element modeling and analysis very difficult, because the size of the field is larger several order than the gaps’. In order to overcome the problem, based on the analytical solution of the gap flow, the seepage field was divided into outside and inside parts. In the outside, the flow was modeled by half a well whose diameter equals the gap width. In the inside, the flow was modeled by a uniform flow. Between them a local additional hydraulic head emerged. A coefficient was deduced to take into account the local hydraulic head loss. With the coefficient and the well point hydraulic head modified method which is employed in seepage finite element analysis, a modified line element formula was gained. The formula accuracy was examined. Using the modified line element to model gaps, in neighborhood of gaps inlets or outlets, the element size can set to be one-third to one-fourth of buildings side length without losing accuracy. Examples show that modified line element can model gaps between buildings precisely and efficiently. It can greatly reduce complexity of using finite element method to model an urban regional seepage field.

Key words: urban groundwater, seepage, groundwater environment, gap, finite elements