The Strength Properties Of Unsaturated Loess And Nonlinear Constitutive Model

Focused on the unsaturated loess, the characteristics of the unsaturated loess such as shear strength, structural strength, deformation, damage evolution, porosity evolution were scheduled systematic experimental study and deep theory analysis in this paper by means of direct shear, unsaturated triaxial tests and computerized tomography. According to the above test results, a nonlinear damage constitutive model of unsaturated soil was developed.Firstly, a series of unsaturated loess tests were carried out under matric suction testing, shear strength, structural strength, unsaturated triaxial tests. In the trial above the foundation, the numerical value that the shearing strength formula with unsaturated soil was obtained with the saturated soil shearing strength formula had carried on the comparison, and points out with the unsaturated soil strength parameter more is close to in reality, and the construction have the fixed guidance meaning to the engineering. According to the research of the structural strength of unsaturated Q3's loess, this paper put forward with shearing strength by expressed with structural strength, for the shearing strength of unsaturated soil of calculation has provided one kind of simple and convenient practical method. Apply three apparatuses in the unsaturated soil, and has carried on three trials of control suction, and has built the nonlinear model of unsaturated loess above the foundation of trial to unsaturated loess. This model parameter is defined simply, and the parameter all has definite physics meaning in the model, is Duncan -zhang model generalization.Secondly, with a triaxial test instrument for unsaturated loess which can work with computerized tomograph carried original Q3 and Q2 loess testing on instantaneously, quantificationally and undamaged scanning. Combining CT images, data and stress-strain curve, this paper divided shearing process into 4 period with respectively analyzing studying. The author has put forward how to decided initial damage stress and strain threshold value of the unsaturated loess and defined damage variable by CT's number. This work has established the foundation for the damage constitutive model of the unsaturated loess, which has the very important meaning.Finally, based on the composite damage theory, this paper suggested a nonlinear damage constitutive model of unsaturated loess, which include 13 deformed the parameter by testing. This model can reflect the mechanics property of unsaturated loess of original state completely, and opened up the new way for damage mechanics the application in the soil engineering aspect. This thesis applied the damage data testing by CT machine to the damage model for the first time, which is a try that the undamaged CT technique used to the damage constitutive model.