A Study On The Strength Characteristics And The Constitutive Model Of Unsaturated And High Liquid Limit Red Clay

Nowadays，the research of the unsaturated soil becomes the hot topic in the soil mechanics.The key characteristic of the unsaturated soil can be focused on its strength properties andconstitutive model. This report is to analyse the unsaturated and high limit red clay underlyingthe existing theory of the unsaturated soil. Through the unsaturated triaxial test we can discoverthe impact on the high liquid limit red clay strength and deformation characteristics by assessingthe confining pressure, matrix suctions such kinds of stress state variables.This report comprises of five points to be analysed:1．Using the unsaturated triaxial apparatus to carry out the unsaturated triaxial test bycontrolling the degree of the matrix suction, we can find out the influence on the unsaturatedsoil shear-strength and the unsaturated intensity on the high liquid limit red clay as well. Theresult is if the matirx suction becomes more higher, the more cohesive force of high liquid limitred clay will be. Whereas, the matrix suction palys an insignificant impact on the internalfriction angle.2．By utilising unsaturated triaxial apparatus, the soil-water characteristic curve can bedrawn out under the low confining pressure soil-water characteristic test. The curvedemonstrated that the high liquid limit red clay has a good water lasting quality. Linearrelationship of fitted curve has been discovered by fitting the soil-water characteristic curve.3．According to result of the unsaturated triaxial test and soil-water characteristic test, theformula can be formed between the relationship on the water content and the unsaturated soilshear-strength, which was based on the Fredlund’s formula.4．Duncan-Change Model applies constitutive model parameters to the research of the highliquid limit red clay, by analysing the stress state variables that may affect the soil deformation.The result illustrated if under the same net confining pressure, the greater the matrix suction, themore tangent modulus of elasticity and volume modulus of deformation will be. Meanwhile,with the same matrix suction, the net confining pressure has press character on soil, thatconfining pressure to enhance the role of soil strength. The tangent modulus of elasticity will bekept the same pace with the level of the net confining pressure, however, and net confining pressure won’t impose on the volume modulus of deformation very much.5．By putting forward the dual-line method to calculate the coefficient of liquid volumechange, it is concluded that the effect of matrix suction on liquid-volume-change is almost twicethan the net confining pressure on liquid volume change.