Constitutive Model And Slope Stability Evaluation And Its Application For Unsaturated Expansive Soil

On the basis of review and summary about the published achievements of the research on the unsaturated expansive soil theory, slope stability and its reinforcements, soil-water characteristic curve is applied into practical engineering, and a new shear strength formula is put forward, and superficial landslide characteristics and its reasons are analyzed according to field monitoring data, triaxial tests of unsaturated soil, numerical simulation and program development. Based on expansive soil tests the paper points out shortcomings of Barcelona Model, and modifies the Barcelona Model in terms of triaxial tests of unsaturated expansive soils. Main research findings can be obtained as follows:(1) On the aspect of monitoring data and tests, matric suction of cut expansive slope usually varies in a more extent than that of natural expansive soil slope, and presents the characteristics of bad rule and obvious dispersity. There are different weathering depths for different parts of the slope. It is known from the tests that cohesive force and frictional angle of unsaturated expansive soil are both a function of suction, and are fixed values when suction arrives at infinite.(2) On the aspect of theory, the paper expresses soil water characteristic curve with a sectional polynomial, which possesses high precision and is available to resolve shearing strength and permeability coefficient of unsaturated soil. Soil water characteristic curves obtained by the triaxial apparatus, from which air enter value (AEV) and residual saturation (RS) are difficult to gain, are different from those of in-situ monitoring. The paper puts forward a new shearing strength of unsaturated soil according to a kind of effective stress and the soil water characteristic curve. And triaxial tests of unsaturated expansive soil have approved practicability of the unsaturated shear strength. Based on the test data, the paper points out shortcomings of the Barcelona Model. Assumption of p_s = ks leads to occurrence of tension stress form LC in the Barcelona Model. In the Model ratio of slope of Critical State Line M is considered as a fixed value, which conflicts with triaxial tests of unsaturated expansive soil. The paper modifies the Barcelona Model by introducing nonlinear expression of M(s), which has been validated by the testing results. In the...