Prediction of Behavior of Soft Grounds in Polder Due to Embankment

采用有限元法对小岛和笠冈湾区填海造地五个项目的软土地基进行了固结分析。采用纸板排水法、填砂排水法和压砂桩法对软土地基进行了治理。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条件下进行的。分析所需的土体参数，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。将观测数据与计算结果进行比较，得出以下结论：1)所提出的方法可以预测三种不同方法加固后软土地基的沉降。轴对称分析能较好地估计纸板和填料排沙法加固地基的观测值，而对压砂桩法加固地基的规定位移进行的分析表明，实测沉降与计算沉降的趋势相似。2)利用观测沉降进行反分析，得到二次固结开始时间和二次固结系数。3)孔隙压力的估计差值程度（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。而D_<ED>的变化率没有变化。D_<ED>和D_<ED>程度的速率随X/L的增加而增加。4)堤防中部D_< ed>较低值为0.5% ~ 24%。5)小路堤区D_<ED>较大，但D_<ED>的变化率几乎为零。宽路堤区D_<ED>和D_<ED>变化率值较小。

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.