The Research On Effects Of Sample-preparing Methods On Anisotropy And Shear Band Of Fine Sands On Digital Image Measuring System

Tri-axial test plays an important role in the developing of Geotechnical Engineering. It can be used to determine the strengh of soil to rearch the relations of stress and strain when shear. Static tri-axial test with the application of computer digital image measuring technique can not only realize non-contact measuring of soil specimen strain when shear, but also measure the change of deformation of the soil specimen when consolidation.The triaxial consolidated drained shear tests were conducted for loose and dense saturated Tangshan fine sand sampled with different initial sampling water content. By measuring the deformations of the axial and radial direction used digital image measurement system, the change relationship of the axial strain and radial strain during consolidation drained process was acquired. By drawing the filed figures of axial strain and radial strain, the change rules of two strain fields were analyzed. The stress-strain curves of saturated samples with different initial sampling water content during shear process were obtained. The test results shown that saturated samples prepared with different initial sampling water content had different initial structure, samples prepared with wet method and dry method behaved different deformation properties in consolidation drained process. The relations of stress-strain during shear process for loose and dense sand were effected by the initial sampling water content. The fundamental reason is that different initial sampling water content has a great impact on initial structure of saturated sand samples.By used the axial strain fields, the process from the beginning of strain localization to growth and forming of shear band was analyzed. The test results shown that strain localization is apparent, by which the characteristic points of the beginning of strain localization and the forming of shear band were determined.; the increase of partial lateral strain of sand inside the shear band was much more larger than that outside shear band, relatively unstable. The increase of overall axial strain was mainly due to relatively large axial strain resulted in shear failure of sand inside the shear band, compressive deformation arising from the soil itself had smaller proportion in the overall axial strain of samples.