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

本研究的目的是寻找土壤沉降环境与地基工程性质之间的关系。研究结果总结如下：(1)絮凝体的形成过程及其沉降沉降对天然粘土的大空隙比结构具有重要作用。(2)在实验室条件下，通过在粘土浆中加入少量水泥，可以再现老粘土的大空隙比结构。(3)对海相粘土进行了流水条件下的沉降固结试验。当水流较大时，由于侵蚀和固结的反复作用，黏土高度呈阶梯状下降。流动水固结黏土的抗剪强度大于静水固结黏土的抗剪强度。(4)超过液限的高含水率软底泥浆在波浪诱导压力下流化时，泥浆表面产生裂缝。裂缝是在波的周期性运动中主应力的旋转所引起的拉应力和剪应力的作用下形成的。通过试验和数值研究，阐明了波浪作用加速泥浆固结的机理。(5)含10%细粒的沙土在循环水压变化作用下，细粒在土中向上移动，最终到达地表。当水压降低，地表超孔隙压力较大时，细粒向上移动。认为循环水压变化下液化的发生与颗粒的向上运动密切相关。

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.