Research On Structure Parameter Of Loess And Structure Constitutive Relations Under Ture Tri-axial Condition

Structure characteristic is the essential property of natural soils. That it is complicated in qualitative and quantitative makes the study in the "each airs his own views" groping moment.In this paper,based on known research of soil structure and its mechanic effect,the change law of structure property and its strength or deformation constitutive relations have been studied by new true tri-axial apparatus in the theory of comprehensive structure potential.The results are as follows:Firstly,the new true tri-axial apparatus has been debugged and perfected that it was developed by xi'an university of technology. Some key technical problems have been amended,for example, leakage of hydraulic pressure bursa, control of drainage,analysis of apparatus system error, design of accessorial equipments,and so on.In the mean time,the test methods have been summarized detailedly and the limitation of true tri-axial apparatus has been put forward.Secondly,the stress-strain characteristic of intact loess,remolded loess,saturated loess have been researched by tri-axial apparatus.A new structure parameter which is stress ratio structure parameter was proposed that it can reflect the coupling action of shear stress and mean spherical stress.The change law of structure property has been analysed and the relationships between structure parameter and shear deformation,water content, consolidation pressure, stress path have been recognized systemically. The four kinds of failure formation of sample was advanced in true tri-axial condition.Thirdly, based on the relation between strength and structure property,a new strength criterion that it can consider structure property has been proposed and the relations between cohesion force or internal friction angle and structure parameter have been established. It is shown that the structure parameter ratio is in direct proportion to strength ratio.The relation between structure parameter and cohesion can be described as hyperbola.When the soil structure have been destroyed completely,the cohesion is equal to O.The internal friction angle is invariable.Fourthly, The relations between the size or shape of failure surface and structure property have been discussed.The stronger the structure property is, the more the contribution of cohesion force to strength is.So,the strength is equivalent in the condition of tri-axial compress and extrusion.The strength failure surface can be described by Mises criterion for strong structure property soils.When the structure property is weak, the contribution of cohesion force to strength is small and the strength failure surface can be described by Mohr-coulomb criterion.The strength failure surface would be expanded as the increasing of structure parameter.Fifthly,Some new relations have been proposed that it includes qusi-pre-consolidation pressure,the linear moment and rebound slopes of condensation curves with structure parameter.The elastic-plastic models of structured soils have been established combining the change law of strength and deformation based on the analysis of the critical state property for structured soils under the condition of same structure parameter and Cambridge Clay model. The new models introduced a critical state line which moves based on structure parameter,and which can reflect deformation characteristic of structure soils rationally.The Cambridge Clay model is special one of the new model when structure parameter is equal to 1.The research was supported by china natural science fund "Research on Strength and Deformation Theory of Structured Soils Based on Comprehensive Structure Potential" (No.10872161).