Research On The Constitutive Model Of Unsaturated Structured Loess

The study on stress-strain characteristics and constitutive model for natural loess is an important research direction in the field of loess soils mechanics.Structure and unsaturation are the essential nature of naturally deposited loess,which has considerable influence on the strength and stress-strain response of natural loess.Therefore,based on the former researchers' achievement of the theoretical research on loess structural and unsaturated properties,by physical interpretation,theoretical formulation and the establishment of constitutive model for natural loess,the dissertation was focused on the study on the deformation behavior and strength character of natural loess combined with structural yield characteristic and unsaturation.An elasto-plastic constitutive model for structural and unsaturated loess has been elaborated,which can describe simultaneously the effects of the coupling of hydraulic and mechanical properties.The main aspects and achievements of this thesis are as follows:1.An elasto-plastic constitutive model was established which can consider the coupling of hydraulic-mechanical properties for normally consolidated and over-consolidated remolded loess.On the framework of the critical state theory of unsaturated soils,improving the LC yield curve of BBM model,refering to Wheeler's method for bilinear soil-water characteristic curve,the relationship among suction,soil deformation and saturation was established to reflect the change in soil-water characteristics of unsaturated soils.In addition,combining the subloading modified Cam-Clay model and modified hydraulic-mechanically BBM,the purpose is expand the modified BBM model to overconsolidated unsaturated soils for better simulation of overconsolidation effects on strength and deformation of unsaturated remolded loess.By comparisons of the proposed model and the overconsolidated unsaturated soil constitutive model proposed by Yao and BBM model.The advantages of proposed model are shown in reflecting the mechanical properities of unsaturated soil.Validity of the model is verified by groups of experimented results for different loess.2.An elasto-plastic constitutive model for the natural normal consolidation loess was established,which can describe both structural and unsaturated properties.Due to the constitutive model proposed in Chapter 3 was established on the basis of remodeling loess,the structural damage characteristics of natural losee is not reflected reasonably.Improving the evolutionary rules of the structural parameters proposed by Asaoka,a constitutive model is proposed to describe the structural and unsaturation characteristics of natural loess on the basis of the former model.When the effect of unsaturation is not considered,the model degenerates into a constitutive model of normally saturated structural soils.Validity of the proposed model is verified by the test results for several groups of typical unsaturated natural loess.The effects of loess of structure and unsaturation are well captured by the proposed model.