Finite element consolidation analysis of soils with vertical drain

This paper presents a finite element procedure for the analysis of consolid ation of layered soils with vertical drain using general one-dimensional (1 -D) constitutive models. In formulating the finite element procedure, a New ton-Cotes-type integration formula is used to avoid the unsymmetry of the s tiffness matrix for a Newton (Modified Newton) iteration scheme. The propos ed procedure is then applied for the consolidation analysis of a number of typical problems using both linear and non-linear soil models. Results from this simplified method are compared with those from a fully coupled consol idation analysis using a well-known finite element package. The average deg ree of consolidation, excess porewater pressure and average vertical effect ive stress are almost the same as those from the fully coupled analysis for both the linear and non-linear cases studied. The differences in vertical effective stresses are tolerable except for the values near the vertical dr ain boundaries. The consolidation behaviour of soils below a certain depth of the bottom of vertical drain is actually one-dimensional for the partial ly penetrating case. Therefore, there are not much differences in whether o ne uses a one-dimensional model or a three-dimensional model in this region . The average degree of consolidation has good normalized feature with resp ect to the ratio of well radius to external drainage boundary for the cases of fully penetrating vertical drain using a normalized time even in the no n-linear case. Numerical results clearly demonstrate that the proposed simp lified finite element procedure is efficient for the consolidation analysis of soils with vertical drain and it has better numerical stability charact eristics. This simplified method can easily account for layered systems, ti me-dependent loading, well-resistance, smear effects and inelastic stress-s train behaviour. This method is also very suitable for the design of vertic al drain, since it greatly reduces the unknown variables in the calculation and the 1-D soil model parameters can be more easily determined. Copyright (C) 2000 John Wiley & Sons, Ltd.