Research On The Inherent Anisotropy And The Deformation Of The Whole Process Of CD Test Affected By Sample Preparation Method

It's important to simulate the natural soil to study the mechanical properties by using the suitable sample preparation method in laboratory test.For the current research,more studies were focused on the difference of shear properties about the sample preparation method than the development of deformation and the inherent anisotropy during the sample saturated and consolidation which are neglected by researchers.The axial and radial deformation of the vary densities of saturated Dalian river sand and Nanhai calcareous sand made by different sample preparations were measured by the whole-surface digital image measuring system,and the deformation characteristics of isotropic were achieved under the condition of static triaxial isotropic loading and unloading consolidation test.The impact of size effect to the inherent anisotropy was studied by comparing the difference of anisotropy between 39.1mm in diameter,high 40 mm samples with the same diameter but 80 mm in height samples.The reliability of the whole-surface digital image measuring system was verified by the contrast test made by true triaxial apparatus for the river sand of 50% relative density made by dry tapping method.The results of static triaxial isotropic loading and unloading consolidation test show that sample preparation have an effect on inherent anisotropy for one sand,river sand made by dry tapping show more isotropic than that made by moist tapping,calcareous sand made by dry tapping show more anisotropic than that made by water pluviation;differences exist in the two sands made by the same sample preparation,river sand is more isotropic than calcareous sand which all made by dry tapping;the inherent anisotropy is related to density and sample size,distinctly difference emerges between the two sands.And the feasibility of using the whole-surface digital image measuring system to study the inherent anisotropy is verified by the similar results of true triaxial and static triaxial tests.The influence of the development of deformation and the change of the density during saturated and consolidation for loose and dense river sand and standard sand made by dry and moist tapping in consolidation drainage test to the shear characteristics is studied using the whole-surface digital image measuring system,and then the stress-strain relationship has been compared between saturated and dry sand made by dry tapping method.The results of consolidation drainage tests indicate that the characteristics of deformation during saturatedand consolidation is different because of the sample preparation,especially for the river sand made by dry tapping which greatly affected by air-free water when saturated;the sample made by dry tapping is more denser than that made by moist tapping,which leads that the peak stress of dry tapping sample is higher than the moist tapping sample during the process of shearing,but not the standard sand which the moist tapping sample is denser than the dry tapping sample and the stress-strain relationship don't show the significant difference.The change of density may rasult in the different shearing propertie between the dry tapping sample and the moist tapping sample,but the main reason is the distinct structure characteristics which made by sample preparation.The constant head permeability test of70% relative dense river sand and standard sand is made for this purpose,the influence of sample preparation to the sample internal pore structure characteristics is analyzed preliminary,the results show that the permeability coefficient of wet sample is larger than dry sample.The pore structure characteristics is distinct different because of the difference arrange of granules caused by sample preparation,which affect the permeability coefficient.This prove that sample preparation have an effect on internal pore structure characteristics on the macro level.