Plane Strain Finite Element Analysis for Consolidation Settlement in Soft Ground Improved with Packed Sand Drains

A practical study on behavior of soft ground in reclaimed land (III)

Abstract

This paper discusses an application of the linear elastic finite element method for settlement analysis of the soft ground in Kasaoka-Bay reclaimed land. The ground had been improved with packed sand drains and preloading embankments.
The consolidation of the improved ground should be analyzed three-dimensionally. However, we have had many difficulties in conducting a three-dimensional analysis. Kobayashi has proposed an approximate plane strain analysis using modified permeability in an improved area.
The applicability of Kobayashi method is examined in this paper. The method is preliminarily applied to a plane strain analysis for the effective area of a packed sand drain.The calculation results are then compared with the solution of the Barron equation. Second, the plane strain analysis for the reclaimed land is carried out with Kobayashi method. The calculation results are also compared with observed settlements. The original soil constants for the analysis were determined from the oedometer tests.
Consolidation analyses sometimes fail to estimate settlements correctly. A method for modifying the soil constants with observed data is accordingly proposed. The method modifies Young's modulus with the ratio of the observed settlement to the calculated one.
The concluding remarks of this paper are as follows:
1) The preliminary results of the plane strain analysis with the Kobayashi method are fairy close to the Barron solution. However, the settlements are smaller at the latter part of consolidation.
2) The calculated settlements of the reclaimed land are 25% smaller than the observed ones after the completion of the preloading embankments.
3) The settlements predicted with modified Young's modulus agree with the observed ones satisfactorily. However, the predicted settlement of the point near the edge of the preloading embankment is different from the observed settlement when the adjacent embankment was rapidly constructed.