Relationship between deviator stress and axial strain of unsaturated loess under coupling of stress and moisture

In order to obtain the formula of relationship between deviator stress and axial strain under coupling change of initial degree of saturated and deviator stress, the consolidated-drained triaxial tests are conducted on Xi´an undisturbed loess under different water contents. Based the principle of equivalent deformation, the equivalent deviator stress of structure is defined by using deviator stress difference between unsaturated and saturated loess under the same confining stress and axial strain. The conception and method of effective stress principle and the equivalent stress of structure and fluid on unsaturated loess are developed from compression stress to triaxial stress. The expression of effective deviator stress of unsaturated loess is established under triaxial stress. Relations between equivalent deviator stress of structure and degree of saturation as well as deviator stress are investigated. The formula of equivalent deviator stress of structure is proposed which can reflect coupling of moisture and stress. According to the expression of effective deviator stress and equivalent deviator stress of structure under triaxial stress, the formula of relationship between effective deviator stress and axial strain of unsaturated loess is established on the basis of hyperbola formula of saturated loess by using initial degree of saturated and stress as variables. For a sort of unsaturated and saturated loess, the formula has general parameters. The relationship between deviator stress and axial strain and that between effective deviator stress and axial strain as well as the tangent modulus can be calculated under coupling or respective change of initial degree of saturated and deviator stress by the formula. The calculating results are accord with the test results.