Experimental Study On Rheological Properties Of Loess

In the various studies of loess landslide disasters,the mechanism of initiation and movement of loess mudflow has been noticed for many years.It has been pointed out by previous studies that the movement characteristics of the loess mudflow are similar to the viscous fluid.However,the rheological properties of loess have not been systematically studied,and rheological properties test research is scarce.In order to deepen the research,this thesis analyze the rheological characteristics of loess with the change of basic physical properties,and provide scientific parameters for the loess mudflow.In this thesis,the rheological properties of the loess samples are studied by rheometer and viscometer.Through a series of experiments,the rheological properties of the samples under different basic physical conditions are obtained,and the effects of water content,size distribution,solution salt concentration,salt washing process and flow process on the rheological properties of loess are analyzed.In order to study the effect of water content on the rheological properties of loess,the rheological properties of natural samples under the test conditions are tested using the rotation test of the rheometer.The rheological parameters are fitted by the Bingham model and the Herschel-Bulkley model.The relationship between the rheological parameters of the sample and the water content is analyzed.The variation of the apparent viscosity of the sample with the shear rate is summarized,and the experimental results are analyzed.The rationality of the test results is verified by comparison with previous research results.In order to further research the static structural characteristics of the loess and observe the response of external forces,an amplitude sweep test and a creep test are set up to investigate the state change of the sample with shearing motion and verify the rationality of the rheological parameters.In order to study the influence of particle size distribution and salt concentration difference on the rheological properties of the sample,the effects of different particle size distribution and different salt concentration on the rheological properties of the manually formulated Shichuan sample are tested by the rotation test of viscometer.The effects of salt washing and flow behavior on the rheological properties of the samples are analyzed.The rotation test results of the rheometer show that the loess has characteristics of a shear thinning fluid.The water content has a great influence on the rheological properties of the sample.As the water content increase,the yield stress,plastic viscosity and consistency factor of the sample decrease rapidly and the liquidity index had no obvious law..The response of yield stress to moisture content is more pronounced than plastic viscosity and consistency factor.The Herschel-Bulkley model is better than the Bingham model in fitting the shear rate-shear stress relationship.As the moisture content increases,the flow characteristics of the sample will gradually approach the Newtonian fluid properties.The results of the amplitude sweep test show that as the shear strain of the sample increases,the viscoelasticity of the sample is weakened and the fluidity is enhanced.When the stress strain reaches a certain level,the solid-liquid state transition occurs in the state of the sample,and the shear stress required for the conversion decreases rapidly with the increase of the water content.The creep test results show that the yield stress of the Bingham model is more consistent with the Herschel-Bulkley model.The test results by the viscometer show that the increase of the fine particle content and the salt concentration of the sample leads to an increase in the yield stress,plastic viscosity and consistency factor of the sample.The samples show significant shear thinning under various conditions.The main reason is that with the content of clay particles increases,the collision and adhesion probability of particles increase under the same volume concentration,and the flocculation effect is enhanced.With the increase of salt concentration,the thickness of the electric double layer between the clay particles gradually compresses,the electrostatic repulsion between the particles decreases,and the sample is more likely to flocculate.Therefore,when the fine particle content and the salt concentration are increased,the yield stress,plastic viscosity and consistency factor of the sample increase.For the samples obtained before and after the mudflow,the salt content is not much different,and the fine particle content is reduced after the mudflow,yield stress,plastic viscosity and consistency of the sample are all reduced.For the samples before and after salt washing,although the salt content of the sample is reduced,the content of fine particles is increased.Under the opposite effects,the influence of the particle size distribution is greater than the influence of the salt concentration on the sample,lead to the rheological properties of the sample changed eventually.In this thesis,the loess samples under different basic material properties are systematically set up.The effects of moisture content,particle size distribution and salt concentration on the rheological properties of loess are studied by a large number of experiments.For further study,the rheological properties of loess samples are analyzed for both salt washing and mudflow processes,which provided basic experimental parameters for the study of loess rheology.The experimental study on the rheological properties of loess will be of great significance for the monitoring and early warning,disaster prevention and risk assessment of loess mudflow in the Loess Plateau.