Study On The Characteristic Of Soil Anisotropic Deformation By True Triaxial Test

Soil anisotropic deformation is one of the important problems of geotechnical engineering and theoretical research of soil mechanics, but many phenomena and laws of it have not become well known and have not been fully acquaintanted up to now. The research of that problem is restricted by test means besides its intrinsic complicacy. It is difficult for soil anisotropic deformation characteristic to be studied without true triaxial apparatus and true triaxial test. A valid method to make the anisotropic deformation behavior of load bearing unit clear is to research principal stress and principal strain relationship, and true triaxial test is a necessary means.Many computational analysis of soil constitutive models appear to be irrational because of taking no account of or not thoughtfully considering the anisotropic deformation when they face the direct or indirect simulation of principal stress and principal strain relationship of load bearing unit. Stress and deformation of computational analysis is usually not in conformity with actually observed data due to this reason in FEM analysis of earth dam and CRFD such as the extensively applied Duncan-Chang hyperbolic model, and many other models also equally have similar problem. Therefore, soil anisotropic deformation characteristic is the key problem concerned by this paper.The research of soil anisotropic deformation characteristic in this paper is mainly to study the anisotropy of lateral deformation and the anisotropy of principal stress and principal strain relationship in different load direction. Three different aspects of anisotropic deformation including lateral strain, relative proportional relation of lateral strain and strain in load direction , and train increment induced by unit stress increment in load direction will be delicately analyzed. The stress strain relationship in different principal stress load direction can be reflected in the anisotropy of tangent elastic ratio or strain increment in load direction induced by unit stress increment in load direction. These three aspects of anisotropic index can be sufficiently embodied in the property of compliment matrix of anisotropic elasticity and compliment marix of principal stress and principal strain relation with general sense. So the research of anisotropic deformation in this paper emphasizes particularly on the analysis of the property of the compliment matrix reflecting anisotropic characteristic in order to analyze some new phenomena and reveal some laws of anisotropic deformation.Former true triaxial test research have been lack of the completely study on soil anisotropic deformation characteristic on condition that load in each of the tree principal stress direction because of their different research purpose. Although true triaxial apparatus is unpopular so far, Hohai university has recently designed and manufactured a set of new style true triaxial apparatus, which provides this paper with essential condition to study soil anisotropic deformation characteristic.It is discovered that the domestic and foreign true triaxial apparatus already designed and manufactured have their individual merits and faults during debuging and testing the new true triaxial apparatus of Hohai university.Thus, firstly, the quality of the main domestic and foreign true triaxial apparatus is analyzed and evaluated , and some constructive opinions of designing and manufacturing more reasonable, stable, accurate and dependable domestic true triaxial apparatus in the future are brought up.Secondly, true taixial test by load in three different principal stress direction for study on soil anisotropic deformation characteristic are processed. Lateral deformation relative to load direction, lateral deformation relative to lateral direction and the stess-strain relationship in load direction are analyzed, and soil anisotropic deformation characteristic on the three aspects of elastic ratio, Poisson' s ratio and the property of compliment matrix are completely analyzed too. Some new phenomena and la...