Abstract
In EFG applied to a soil/water coupling problem, the instability of pore water pressures was verified using the Zienkiewicz-Taylor patch test. In EFG, displacements and pore water pressures are approximated at all nodal points using the shape function that computed by the basis function of same order. Because simultaneous equations don't satisfy so called the inf-sup condition. The patch test was performed on various conditions. And it has checked that coefficient of permeability, shape function and density of nodal points had great influences on the instability of pore water pressure.
