Study On The Microstructure Of Holocene Lacustrine Sediments In Tianjin Binhai New Area

For many years,a lot of studies on the microstructural feature of soil have been made. A variety of research methods or technologies have been employed in soil microstructural investigation. But the previous studies on the soil in Tianjin Binhai New Area mainly focused on marine soil and hydraulic fill,few studies are involved with lacustrine soil. However it is well known that in Tianjin Binhai New Area many engineering problems,such as roadbed subsidence,storehouse foundation stability etc,are involved with the upper lacustrine sediments, therefore study on which is of theoretical and practical significance.(1) The physical property, chemical composition and mechanical property of lacustrine soil in Tianjin Binhai New Area are studied based on the test. It is found that the lacustrine soil in Tianjin Binhai New Area is predominated by fine-grained clay and belongs to unfavorable gradation, has high liquid limit, strong compressibility, low strength and poor permeability. It is clear that it can not be used as engineering ground and must be treated.(2) Because macro-mechanical property of soil is the reflection of micro-structure variation, to study the structural constitution of lacustrine soil which had been processed with low-temperature and vacuum free-drying, electronic scanning microscope is used to obtain the microscopic scanning picture of lacustrine soil, and picture processing software is used to obtain the microstructure parameters. Equivalent diameter, number of pore, perimeter of pore, area of pore, shape ratio of pore, roundness of pore, orientation frequency of pore complexity are selected to impress the size, shape and arrangement of pore in lacustrine soil.(3) In order to study the microstructure mechanism of lacustrine sediments during the consolidation compression and shearing failure, the relation between micro-structure parameter of the soil sample and the load under different load condition have been carried on. The research indicates that the micro-structure of lacustrine soil shows regular change under different load condition, Which further indicates macro-mechanical property of soil is the reflection of micro-structure variation.For example, under different consolidation pressures , as the porosity of soil reduced,the pore number increased,but the pore diameter reduced.(4)In this paper, the fractal dimension of particle and pore was computed by using fractal theory in order to researched on lacustrine soil furthermore.When relate fractal dimensions of particle to explain mechanism of consolidation,we can find that fractal dimensions are good to explain character of reinforce soil.Someday the fractal theory can be used to practice of injudging intensity of foundation soil,which is of theoretical and practical significance.