Study On The Evolution Characteristics And Constitutive Model Of Loess With Compressive And Shear Moisture Damage

Loess is a kind of unsaturated soil with natural structure.It's exactly because of the special structure of the loess soil that it is different from other soil types'engineering properties.It's one of the most essential internal factors affecting the macroscopic mechanical properties of loess.Loess and its particle size,density and humidity,which can reflect the strength of soil deformation,mechanical properties,is one of the basic reasons for the change of mechanical properties of loess.In this paper,we carried out a research on significant structural loess,aiming at the loess structural damage deformation characteristics.Based on the analysis of the rules from the loess structural damage deformation of undisturbed loess unconfined compression test and the triaxial shear test,we put forward a pattern which can describe undisturbed loess's change from steady state to damage state.Combining with the rock damage mechanics theory,we proposed a structural damage factor(namely damage ratio)which can reflect the effect of loading and increased wet.Then we established a one-dimensional compression model and a loess structure damage elastoplasticity constitutive model considering the effect of load and humidification.The main research results are:Firstly,in view of the shortcomings of the previous scholars' study on the completely damage soil(no structural soil),we developed a normal consolidation soil preparation device instead of previous way which used the saturated artificial soil to simulate the normal consolidation soil.The device can be used to prepare samples which are similar to the normal consolidation soil properties,and two methods of controlling the sample dry density of normal consolidated soil are put forward.Secondly,based on the undisturbed loess and normally consolidated loess side limit compression test,according to the deformation of the specimen and charge state,undisturbed loess deformation damage mode and strength damage model are proposed.Furthermore,according to the two kinds of damage modes,the determination method of structural deformation damage ratio and structural damage ratio was pointed out,and the expression of one-dimensional compression model considering the damage evolution of the original loess was deduced.Thirdly,according to the relative position of the compression curve of undisturbed loess and normal consolidation loess,the undisturbed loess structural damage initiation pressure was determine,and the structure damage initiation pressure divided the load deformation of intact loess into two groups,that is the elastic deformation and plastic deformation.A critical state model for the damage of undisturbed loess structure is presented.Fourthly,according to the matrix suction's measurement result of different humidity's undisturbed loess under different loads,the notions of peak of matric suction and matric suction of the critical load was put forward.The relationship between the critical load of the matrix suction and the yield stress of the structure was studied.Furthermore,the relationship between the peak pressure and the yield stress of the structure of the undisturbed loess with different humidity was studied.Fifthly,we carried out the triaxial compression test and the triaxial shear test on undisturbed loess and normally consolidated loess with different humidity.We analysed the structural deformation characteristics of loess in isotropic compression and triaxial shear paths.And then we put forward a method to determine the ball stress damage ration and the shear stress damage ration.Sixthly,combined with the preparation method of the normal consolidation soil,we carried out relevant experment and analyzed the yield and failure characteristics.And the rationality of the preparation method of the normally consolidated soil was verified.Seventhly,combined with the damage ratio of the undisturbed loess structure,based on the analysis of the yield and failure characteristics of undisturbed loess,the elastoplastic constitutive model is derived,and the rationality of the constitutive model is verified by experiments.Eighthly,combined with the loess structural damage elastic series model and parallel model and the deduced plastic constitutive model,a new method for the research and testing of the collapsible deformation of the actual engineering in loess area is provided.