A long-term delayed consolidation settlement of naturally deposited soil and its prediction and improvement methods

在路堤荷载作用下的自然沉积粘土地基中，路堤建成后往往会出现延迟沉降，有时还会随着时间的推移表现出加速变形。即使是原状土样，也不能总是根据室内试验结果来预测沉降量。采用原状试件与重塑试件Ccr的压缩指数比Cccr定义压缩指数比Cccr，并用压缩指数比Cccr和敏感指数St.对约50条高速公路的现场沉降数据和室内试验结果进行了估算和分类。采用土-水耦合有限变形分析方法，结合超静载屈服面模型(sysCam-Clay模型)对大延迟沉降的机理进行了探讨。新发现如下：1)长期超前大沉降量的粘土具有较高的灵敏度ST，其值大于8.0，压缩指数比CD Ccr大于1.5。2)在固结屈服应力相同的情况下，通过室内试验对原地压缩性状进行了预测，并在考虑试件扰动的情况下，对长期大沉降量的机理进行了探讨。3)采用土-水耦合有限变形分析与SYSCAM-Clay模型相结合，可以描述长岛地区粘土地基的原地次固结/延迟固结。并提出了在考虑样品扰动的情况下，由室内试验确定现场初始条件的必要性。

In a naturally deposited clay foundation subject to embankment loading, a delayed settlement can often be observed after the embankment's completion, sometimes also showing acceleration over time. The settlement cannot be always predicted from the laboratory test results even with the undisturbed sample. The prediction of the settlement and the long-term period were always underestimated.In the present study, the compression index ratio Cd Ccr was defined by the ratio of the compression index of the undisturbed sample Cc to remolded sample Ccr, and the in-situ settlement data and the laboratory test results on the about 50 expressways are estimated and classified by the compression index ratio Cd Ccr and sensitivity index St. The mechanism of the large delayed settlement is discussed described by using a soil-water coupled finite deformation analysis with the Supre/subloading Yield Surface Cam-clay model (SYS Cam-clay model). The new findings are as follows :1)The clay, which exhibits a long-term large settlement beyond the prediction, can have high sensitivity St, the value of which is more than 8.0 and high the compression index ratio Cd Ccr, more than 1.5. Through the simulation by the SYS Cam-clay model, the clay is a high degree of initial structure and show fast decay of the structure.2)The in-situ compression behavior was predicted from the laboratory test assuming that both the consolidation yield stresses are the same, and the mechanism of the long-term large settlement was discussed taking the sample disturbance into consideration.3)The occurrence of in-situ secondary/delayed consolidation of clay foundation in Nagashima can be described by using a soil-water coupled finite deformation analysis with the SYS Cam-clay model, and it provide that it is necessary to determine the in-situ initial condition from the laboratory test taking the sample disturbance into consideration.