Study on the relationship between environments of soil sedimentation and engineering properties of the ground in Quaternary Era

本研究的目的是找出土壤沉积环境与地面工程性质之间的关系。研究结果总结如下：(1)絮体的形成过程及其沉降性对天然粘土的大孔隙比结构具有重要作用。(2)在粘土浆液中加入少量水泥，可以在室内重现老化粘土的大孔隙比结构。(3)在流水条件下进行了海相粘土的沉降和固结试验。当水流较大时，由于反复冲刷和固结，粘土高度呈阶梯状降低。流水条件下固结的粘土的抗剪强度大于静止水条件下的固结强度。(4)高含水率超液限软泥在波浪压力作用下流态化时，泥浆表面会产生裂隙。裂纹是在波浪周期运动中主应力旋转引起的拉应力和剪应力的作用下产生的。通过试验和数值研究，阐明了波浪作用加速淤泥固结的机理。(5)含10%粉粒的砂土在循环水压力作用下，粉粒在土体中向上方向移动，最终到达地表。当水压降低时，细粒向上移动，地表出现较大的超孔压。结果表明，循环水压变化下液化的发生与粉尘的上移密切相关。

The purpose of this study is to find a relationship between the environments of soil sedimentation and the engineering properties of the ground. The findings of the study are summarized as follow:(1) The process of floc formation and its settling and sedimentation has an important role for the large void ratio structure of natural clay.(2) By adding small amount of cement to clay slurry, the structure of large void ratio structure of aged clays could be reproduced in the laboratory.(3) Sedimentation and consolidation tests of marine clay were carried out under flowing water condition. When the water flow was large, the height of the clay decreased with stair-like pattern due to repeat of the erosion and the consolidation. The shear strength of the clay consolidated under flowing water was larger than that consolidated under the stationary water condition.(4) When soft bottom mud with high water content over the liquid limit is fluidized by the pressure induced by waves, cracks are generated in the surface of the mud. The cracks develop under the action of tensile stress and shear stress caused by the rotation of principal stress in the periodic motion of waves. The mechanism of the acceleration of consolidation of the mud by wave action is elucidated through experimental and numerical studies.(5) When sandy soil containing 10% fines was subjected to the cyclic water pressure change, it was observed that the fines moved to the upper direction in the soil and finally reached to the surface. The upward movement of fines took place when the water pressure decreased and large excess pore pressure was observed at the ground surface. It was suggested that the occurrence of liquefaction under the cyclic water pressure change was closely related to the upward movement of fines.