Prediction of Behavior of Soft Grounds in Polder Due to Embankment

采用有限单元法对小岛和笠冈湾地区填海造地的5个工程软基进行固结分析，分别采用纸板排水沟、填砂排水沟和挤密砂桩法加固软基。安装了测量沉降、侧向位移和孔隙水压力的现场仪器。分析是在平面应变和轴对称分析条件下进行的。用于分析的土壤参数，即，杨氏模量、泊松比和渗透系数由标准固结试验和塑性指数确定。通过实测数据与计算结果的对比，得出以下结论：1）本文提出的方法可以预测三种不同加固方法的沉降。而轴对称分析对纸板和填充砂井加固地基的观测值给出了较好的估计，对挤密砂桩加固地基的沉降计算结果进行了分析，结果表明，挤密砂桩加固地基的沉降观测值与计算值的趋势基本一致利用实测沉降值反分析，可以得到次固结开始时间和次固结系数。孔隙水压力的估算误差度（D_<ED>）随X/L的增大而增大，其中X为测点到路堤边缘的距离，L为路堤宽度。但D_（？）的变化率<ED>不变。路堤中部的D<ED>_值<ED>较低，<ED>在0.5%~ 24%之间; 5）<ED>小路堤区域D_值较大，但变化率<ED>几乎为零。而宽路堤区D_<ED>和D_的变化率<ED>值较小。

Finite Element Method is applied to the consolidation analysis for the soft grounds of five projects in reclaimed lands of Kojima and Kasaoka Bay Area.The soft grounds were improved with card-board drain, packed-sand drain and sand compaction pile method. Installed were field instruments for measuring settlements, lateral displacements and pore water pressure. The analyzes were carried out under the condition of the plane strain and axi-symmetric analysis. Soil parameters for the analyzes, i.e., Young's modulus, Poisson's ratio and coefficient of permeability are determined from the standard consolidation tests and Plasticity index. The following conclusions are obtained from the comparison between observed data and calculated results.1) The method presented herein can predict the settlements of the soft grounds improved with three different methods. While the axi-symmetric analysis gives the better estimation to the observed value of the grounds improved with card-board and packed sand drains, the analysis giving the prescribed displacements for the ground improved with the sand compaction piles method show that the trend of observed and calculated settlements are similar.2) The starting time of secondary consolidation and the coefficient of secondary consolidation can be obtained from the back analysis using observed settlements.3) The degrec of estimation difference (D_<ED>) for pore pressures increases with X/L,where X is the distance of the measuring point from the fringe of the embankment and L is the width of the embankment. However, The rate of change of D_<ED> does not change. Both D_<ED> and the rate of the degree of D_<ED> increases with X/L.4) D_<ED> in the middle of embankments shows the lower value ranged from 0.5% to 24%.5) D_<ED> in the small embankment area is big, but the rate of change of D_<ED> is almost zero. However, D_<ED> and the rate of change of D_<ED> in the wide embankment area indicates small value.