Variation Characteristics Of Soil Structure And Structural Constitutive Relation Of Unsaturated Loess Under Static And Dynamic Complex Stress Conditions

The study of structural constitutive relation of soils is called as "the focus problem of soil mechanics in the 21st century". In this paper, based on the observation and analysis of a large number of literature references, the generous outcomes of study on mechanics properties of loess, obtained in resent years are summarized at following areas of unsaturated soil and dynamic characteristics as well as structural characteristics, and the essential duties of this paper are presented. From the works in this paper, some outcomes are obtained as following:Firstly, with the close consideration of mechanism of forming and changing on soil structure and the soil mechanics approach on study of soil structure, the soil structure quantification description and application is taken as "the breakthrough". From the conclusion of "the regularity is same at strength and deformation of soil and is controlled by structure", the conception and method based on compressive deformation indicated in literature are developed, and a new soil structure quantification parameter is presented and defined based on soil strength. This new soil structural parameter not only makes up for the short of the deformation type soil structural parameter indicated in literature, but also makes foundation for the studying soil structural variation characteristics and establishing the structural constitutive relation under static and dynamic complex stress conditions. Its important impact shows as following aspects: to inherit the reasonable core of pre-outcomes, and to develop the application space of soil structural parameter, as well as to connect the study of soil structural variation both in full-process under the deformation of static and dynamic states.Secondly, based on a lot of test carried through for unsaturated loess(such as intact loess, disturbed loess and men-made structural loess) under the conditions of confined compression stress and routine triaxial stress as well as real triaxial stress, the variation characteristics of soil structure are studied under different tests conditions, and the principalcorrelation factors influencing the loess structure are analyzed, the concerned characters put up in the curves of soil structural parameter are interpreted responsibly, and the rationality of new structural parameter is demonstrated forth more.Thirdly, a lot of dynamic torsional shear test are put up for unsaturated loess under its intact and disturbed states respectively, and dynamic characteristics (especially the variation regularity of pore water pressure and pore air pressure) of unsaturated loess are analyzed under action of dynamic load for the first time. Based on the curves of structural parameter for unsaturated loess, obtained under condition of dynamic test, the viewpoint that similar shape and variation regularity exits in curves of structural parameter of unsaturated loess under the actions of static and dynamic load and these are influenced by same factors of structure is proved. This makes the study of soil structure quantification parameter going into the area of soil dynamic mechanics for the first time.Fourthly, based on the above researches, from the impact analyses of normalization action to the static and dynamic stress-strain relations on unsaturated loess impacted, the oscillatory and regular relations between structural parameter and the deformation-strength characters are opened out, and the structural constitutive relations of unsaturated loess are put forward for static and dynamic complex stress conditions, as well as the upstanding consistency between the results of calculation and tests are validated respectively under conditions of triaxial stress and dynamic torsional shear stress. It is shown that the new structural constitutive relations have the similar basic shape of Ducan-Chang model and Hardin model and their corresponding parameters respectively under the static and dynamic conditions, and they can easily be applied to engineering practice.From the analysis in principle, the research results in this paper...