Study On Relationship Between Microstructure Characteristic And Macro Mechanical Property Of Hangzhou Soft Clay

Soft clay is widely distributed in the southeast coastal area of China, which has the engineering characteristics of high natural moisture content, high porosity, high compressibility, low strength, poor permeability, high sensitivity and strong structure.Research on soft clay has long been based on macro or phenomenological level.However, the microstructure of soil plays an important role in the mechanical properties of soil, which is very significant in engineering practice. A lot of research shows that a series of physical and mechanical properties of soil mass on the macro performance are affected by the state and change of the soil micro structure to a certain extent. On this basis of macrovisual study, it is necessary to disclose the internal relations between the soft clay evolution regularity of micro-structure features and macro-mechanical properties from the microscopic view. Explain the inevitable law of macro mechanical properties of soil from the microscopic physical mechanism to establish a quantitative relationship between macro and micro, which is more in line with the characteristics of soft soil engineering practice.In this paper, the soft clay in Hangzhou and surrounding areas is taken as the research object to carry out scanning electron microscope experiment, Based on the quantitative analysis of its microstructure by statistical analysis, the relationship between microscopic parameters and macroscopic physical quantities of clay is established. The micro structure is introduced to the calculation of soil macro mechanics in order to realize the application of microstructure research.The major research contents and innovation achievements are listed as follows:(1) Quantitative analysis of the microstructure of soft clay in Hangzhou and surrounding areas is made.The porosity of soft clay is studied in a microscopic angle and compared with physical parameters from geotechnical test. Making use of the past's theories and the research result, the relationship between macro porosity of soil and micro average contact area rate is explored.(2) The macro and micro relationship of soft clay is applied to the study of the characteristics of seepage. The commonly used empirical fonnulas of permeability coefficient of coarse-grained soil are modified and similar empirical formulas for clay considering soil contact area are proposed. Substituting the relevant physical parameters of the soft clay several typical areas of China into the empirical formulas of permeability for sand and clay respectively yields the values of the coefficient of permeability. Comparison of the calculated and the measured values confirms the reasonableness of the empirical formulas of permeability coefficient for clay.(3) Starting from the microscopic structure of soil, the shear strength behavior are analyzed. Considering the influence of soil porosity on its shear strength, shear strength theory based on the micro structure is derived.(4) The concept of micro structure is considered in the calculation of bearing capacity of foundation to propose a calculation theory considering soil contact area,from which readjusted critical load factors is derived. An example is adopted to illustrate the proposed method, and results are compared with those by the conventional methods to prove the rationality of this new method.