Abstract: An idea of a disadvantageous width of foundation corresponding a maximum un-drained settlement of ground is suggested in this papar. The proposal is based on the estimation of undrained settlement of subsoil by using the normalized hyperbolic stress-strain relationship. The method is adopted after considering many existing problems in using linear elastic theory for this kind of estimation. An analysis of the re- gularity of the settlement is made here as well as its relevant factors.A series of linear function expressions of the disadvantageous width for varying loads are obtained through linear regression analyses of a large number of computer-aided data and may be of use in some engineering projects.Moreover, the estimating method is checked experimantally by using water tank as a precompression load on the subsoil, the results of its settlement in this test prove the reliability of the estimation.