Study Of Microstructure Characteristics And Bound Water Properties Of The Soft Soil In Binhai New Area In Tianjin

Since the 1980 s, with the rapid development of China’s economy, increasing demand for land in coastal areas is coming, land is a key issue we need to address now. Most lands dominated by soft are distributed in coastal cities, clay particle of the soil is dominant, hydrophilic mineral holds a large proportion of soil, with the reunited with the water structure and connection structure and inter-particle pore is small. As the water evaporates or immersion, the volume of soil shrinkage or expansion, and own a large amount of compression. Engineering construction on soft soil foundation may arise settlement, which may not meet the requirements of construction features such as strength, deformation, and the main cause of this feature is contains a lot of weakly bound water. This is because the arrangement of water molecules is loose, and weakly bound water may gradually migrated from low concentration to relatively high concentration, or migrated from the thicker water film to thin water film. Then the soil structure change, rising low foundation of strength and heavy deformation. For the problem of low intensity and the large amount of settlement caused by bound water, micro-structural characteristics of soft soil and water characteristics of Binhai New area of Tianjin were studied in this paper.In view of low strength and large deformation of soft soil caused by the combined water content change causes, lab experiments was developed and the different soft soil particle composition, mineral composition and physical and chemical properties were discussed in this paper. High liquid limit and plastic index of soil and other special engineering characteristics were analyzed in this study, and low strength, high moisture content, high void ratio, high compressibility of soft soil and other basic engineering properties were discussed in the paper, which provided basic theoretical foundation for further research on soft soil microstructure and hydration characteristics.Second, combined "Scanning Electron Microscope scan test(SEM)" and the "Pressure Mercury Test(MIP)", modern technology means, silt clay, silty clay and silt were selected, three different undisturbed soft soil microstructure characteristics, qualitative and quantitative description of Tianjin Binhai new area of soil pore characteristics and characteristics of microscopic structure unit cell were studied. The soil sample is given priority to with flocculation shape, and the pore and structure unit body distributed as elongated or elliptic shape. Unit cell in silt is bigger, while the structure of the unit cell of silt clay and silty clay is relatively small. Intergranular directionality is poorer, soil particle is thinner, soft clay mineral own the mode connection of edge- edge, the side- edge and a small amount of surface – surface and the pore connectivity is better. It can provide the data parameter for structure characteristics influenced by the bound water.Finally, the volumetric flask method of three different kinds of soft soil was carried out, and four aspects including the component content, temperature and limit moisture content, structure and element were applied to analyze the factors influencing the bound water content. The experimental results indicate:(1) the decisive factor for the formation of bound water adsorption is soft soil mineral surface. As a result of the existence of pseudomorphic phenomenon, it will cause the inadaptability of structure and mineral water. The greater the inadaptability is, the thicker of the combined water film is, which then cause the change of the water and mineral structure. Thus the mineral is the decisive factors influencing the bound water content.(2) The structure of the unit cell is also a factor which influences bound water content, it is found that the more the set of structure element is and the smaller the particle is, the more bound water content is.(3) Temperature is another important influence factor of bound water content. The movement condition of the water molecules will be affected by temperature change. Due to the rise of temperature, water molecules’ movement is more intensified, and the spread of the thermal motion force is greater than the static gravity, which lead to weakly bound water content decreases and bound water film thickness changes. Then the interaction between the soil particles, the soil structure and the properties of the soil particles change, which leads to the changes of physical and mechanical properties between soil particles.