Research On Rheological Model Of Loess In Considering Of Damage Effect

The structural and rheological property of un-saturation loess is the reseach heard of this paper.The microstructure and rheological effect of loess are summarized. According to the result of experiment, a damage variable is determined by using the research methods of soil mechanics, witch can link microstructure to macro mechanical variable. At the same time, the structure damage evolution tendency with the change of water content and plasticity strain are also studied deeply.As a result, the rheological constitutive model of loess is built by using the equivalent strain hypothesis. In the constitutive model, the structure damage effect has been thought out, and it also can be spread to complicated stress condition with the aid of mathematical and mechanical methods.The basic physical property index of MaLan loess(Q₃ loess) in Xi An district, such as chemical composition, cementing material, pore property etc., are summarized after sizing up and sorting out the data that have been collected, and then the experiment of soil mechanics are carried out in order to obtain the change regulation of the macro-parameters of structure strength, cohesin and coefficient of internal friction.The result of CU shear experiment shows the stress-strain relationship of loess is a little soften type, and it can be described by a exponential function with a strength peak in the strain limits of engineering practice. The further research make it clear that the parameters in the constitutive model are variation with the spherical stress and moisture state, and the change regulation can be described by exponential function.According to the results of compress testing to loess in vary stress state, it is clearly that the damage strain threshold has no distinct relation with the water content of loess. Although it can be regarded as a fixed value approximately, the damage stress thresholdis decreasing linearly with the increasing of water content. So is the loess's modulus of elasticity.Based on the hypothesis of damaging to rigidity degree, the damage evolution has no relationship with elastic deformation except plastic deformation history. The damage evolution equation can be described by exponential function of plastic deformation, and the parameter that can reflect the damage rate is influenced by stress and water content. In a broad sense, the water in un-saturation loess has a stress property, because the strain state of loess can be fixed when the change of the water content and the stress state along a given constitution.Q3 loess in variy water content has distinct linear visco-elasticity-plasticity rheological property by the creep experiment. Comparing test result shows that the limit load-bearing capacity can be improved effectively by continue loading in low creep stress, because loading in steps can lead structure of loess to harden. So the loess's limit strength is influenced by loading style greatly. According to the test results, a rheological model that can reflect damage effect of loess is built in the paper, the model can analog accelerate deformation character well.Using of the secondary developing function for ADINA, the finite element program are developed to analog the rheological law of loess, and the rheological model build in the paper has been proved correctly by comparing the result of numerical analog with that of experiment.