Experimental Study Of The Microstructure Of Hangzhou Soft Clay Under Complex Stress Path

Under complex stress path,soft clay’s engineering properties show strong anisotropy,which include the primary anisotropy and the secondary anisotropy. The primary anisotropy and the secondary anisotropy can be studied with the intact clay.The secondary anisotropy can be studied with the remodeled clay which has removed the primary anisotropy. Sample for microstructure observation were made with hollow cylinder clay after the Macroscopic mechanical tests,then SEM pictures are available.Through analysis with the help of PCAS system,the basic geometric parameters and fractal parameters of the observational surface are available.Through the Macroscopic mechanical tests and microstructure observational analysis on Hangzhou soft intact clay and its remodeled clay, conclusions can be drawn:(1) Contrast, brightness and the threshold, which are the main factors of the SEM images, may have important influences on the experimental results. Based on the error analysis, it is found that these factors have some effect on the basic geometric parameters of the observed surface, but the effect on the fractal parameters which are the main parameters in this research is little.(2) Shear test were carried on the intact soft clay under the fixed principal stress axis.The rotation angle do not show noticeable influence on the anisotropy of the intact soft clay. On the contrast,the intermediate principal stress parameter has obvious influence on the anisotropy.The compressibility of the horizon surface is higher than that of the vertical one.(3) Principal stress axes rotation tests were carried on the intact soft clay under fixed shear stress. The effect of the rotation angle and the intermediate principal stress parameter on the fractal parameters is not obvious and regular.Most parameters of this series of tests reach to an extremum when the shear stress is around35kPa, illustrating that the characteristic of the microstructure has dramatic changes.(4) Shear test on remodeled soft clay under fixed principal stress axis were carried. The rotation angle does not have influence on the strength of the remodeled clay.The intermediate principal stress parameter affect the strength of the remodeled clay only when the shear strain reach to a certain value.(5) The pores on the vertical surface of the remodeled clay is more directional,while little difference between the two surfaces of the intact clay.The average pore area of the vertical plane of the remodeled clay is less than that of the horizontal plane,while the vertical plane of the intact clay is less than the horizontal one. Pore area distribution of the two surface is identical.both the intact clay and the remodeled clay.