Unsaturated Elasto-Plastic Constitutive Relation Study Based On Bbm Model For Chuanxi Talus Mixed Soil

This paper takes "the test results contrast with the numerical results of the constitutive model" for the general idea. First conducted a series of laboratory tests for two soil samples from different locations, including the tests of physical indicators in the natural state (mineral composition, water content, density and particle size distribution),unsaturated static triaxial test and unsaturated consolidation test. Analyze the differences of the physical indicator between the two soil samples and study the stress-strain relationship basis on the results of triaxial test, then takes the BBM unsaturated elastoplasitc constitutive model for the basic framework to derive the stress-strain equations of unsaturated soil under the static triaxial stress path and calculate the results of the triaxial tests, finally compare it with test results and summary the applicability of BBM constitutive model for the class of unsaturated mixed soil. The results show that:1. These two samples are similar in particle composition, but they are different in the natural density and water content due to the difference of mineral composition and content, this difference is reflected in the stress-strain behavior.2. Unsaturated tiraxial test results show that:increase of suction and confining pressure improve the soil strength. The impact of the suction on stress-strain behavior of soil sample1is different with soil sample2. In the case of small confining pressure, suction increase case the strain softening of soil sample1, but the phenomenon gradually disappear with the increase of confining pressure and ultimately tends to strain hardening. The soil sample2has strain hardening characteristic under any condition.3. Unsaturated consolidation test results show that:the increase of suction induce soil compression, but also increase its yield stress and there is a yield surface in (p,s) stress space similar to LC yield surface of BBM model.4. For these two mixed soil samples, BBM model applies to strain hardening. For strain softening, it should amends by adding the coefficient about void ratio and stress sate, or select constitutive model which takes the strain softening into account.