Test Research And Engineering Applications Of Unsaturated Soil Constitutive Model Based On Statistical Damage Theory

Soil mechanics development up to now has established the theory of saturated soil maturely. However, unsaturated soil is distributed more widely in engineering practice, and as gaseous phase exists in soil, there are more factors which may affect the deformation of unsaturated soil and display more complex engineering behavior comparing with saturated soil. Taking these factors into account, we can find many defects when the theory of saturated soil is applied to unsaturated soil. This paper aims to investigate unsaturated red clay, and bases on unsaturated soil laboratory test, the theoretical stress-strain behavior of unsaturated soils was analyzed deeply. Through the above, a simple constitutive model of unsaturated soil was proposed according to statistical damage theory, and a new calculation method to settle the deformation of unsaturated soil was presented depending on the model, then they can be applied into engineering practice.The main research content and research results are as follows:1. A series of experimental study about mechanical properties and deformation characteristics of unsaturated soil was conducted based on GDS unsaturated soil triaxial system. The unsaturated soil moisture tests which keep force unchanged and change matric suction in unsaturated soil samples, and the unsaturated soil triaxial tests which keep matric suction unchanged and change force in unsaturated soil samples, indicate that coupling relation between matric suction and external loads may affect the strain of unsaturated soil. The results show that the greater value of the matric suction and net normal stress, the greater ability of unsaturated soil to resist unsaturated soil shear failure.2. On the basis of laboratory test results and existed research results, after taking the statistical damage theory to study about unsaturated soil and using the extended Mohr-Coulomb strength criterion to describe unsaturated soil micro-element strength, unsaturated soil constitutive model is proposed based on statistical damage theory. The proposed simple unsaturated soils constitutive model has several advantages such as fewer parameters and parameters easily to determine, and avoiding the complexity elastic-plastic analysis, so it’s convenient and has some practical value. Compared stress-strain curves of this model with the laboratory test results, the constitutive model is found well to simulate stress-strain curves. Then the key parameters of unsaturated soil statistical damage constitutive model are analyzed and their specific physical meaning is pointed out.3. Based on the layerwise method, unsaturated soil settlement calculation formulas are proposed by unsaturated soil statistical damage constitutive model, and then settlement calculation method is proposed under infiltration. Comparing the computing result by the method this paper proposes with the measured value other methods propose, it indicates clearly that the proposed constitutive model can meet the engineering requirements and has practical value.