Experimental Study Of Constitutive Model For Unsaturated Soils Considering The Effect Of Gas Hardening

An unsaturated soil is consisted of solid, liquid and gas. Most previous researchers presumed that gas is connected with the outside atmospheric pressure so that gas pressure keeps constant under the process of loading. Previous researches have showed that the form of gas has great role in mechanical behavior of unsaturated soils, especially to occluded gas or inner connected gas because of changes of gas pressure. But present studies of this state are little. Most researchers presume constant gas pressure, connected with each other. In addition, most experiments are conducted in low saturation, lacking of data in high saturation and existing difficulties in measuring gas pressure. Although this way has made problem simple, we must accept that there are occluded air in unsaturated soils. How to consider the influence of occluded gas bubbles on soils is an emphasis of this thesis through tests.The target of this thesis is to study the effect of gas hardening on soil behavior and make experimental verification for GAS model, a coupled solid-liquid-gas constitutive model of unsaturated soils. Different with existing test scheme, both high saturation tests and low saturation tests are done so as to the role of gas hardening on soil behavior. Studies has been conducted for silt clay from Beijing through consolidated drained triaxial tests of saturated soils, drying-wetting tests and isotropic consolidation tests of unsaturated soil tests. Parameters of the constitutive model of unsaturated soils considering the effect of gas hardening（GAS model）,proposed by Liu Yan, can be determined by these tests, including the parameters of saturated soils （λ, κ）; parameters of LC yielding surface （k_m, θ）; elastoplastic parameters of fluids （λ_w, λ_a, κ_a）; coupled parameters (k_sw, k_ws, k_sg, k_gs).According to the parameters measured by tests, we make prediction both on high saturation and low saturation. The results show that we should consider the effects of gas hardening on volumetric strain and saturation in high saturation and we can ignore these effects in low saturation. GAS model predicted results can correspond with the tests results both in high saturation and low saturation. So we can make a conclusion that GAS model is effective and show the role of gas hardening to mechanical behavior of soils.