A Study On Dynamic Properties And Microstructure Of Loess In Earthquake Area

As a special deposit in the Quaternary period,loess is mainly distributed in the central and western regions of my country.With the continuous and in-depth advancement of my country's"Western Development"strategy,infrastructure projects in the Loess Plateau area are increasing day by day,accompanied by various construction land problems,such as:uneven settlement of foundations,subsidence of roadbeds,roads The deformation and so on.Therefore,studying the dynamic characteristics of loess has very important practical significance for guiding practical engineering problems in the loess area.However,by discussing the change characteristics of the microstructure of loess under cyclic loading,the dynamic characteristics of loess can be explained reasonably.This article is based on the“Earthquake-induced Loess Landslide Hazard Effects and Risks”subject of the national key research and development program applied by Professor Wang Jiading.The loess of the Xiajia continent in Xiji County,Ningxia Hui Autonomous Region is used as the research object.Axial instrument applied vibration cyclic load to the loess soil sample to study the dynamic characteristics of the loess under different test conditions;then the FEI Quanta 400 FEG field emission environmental scanning electron microscope was used to observe the vibrated soil sample in turn,and compare its microstructure Difference,and draw the following conclusions:(1)The fitting result of the dynamic stress-dynamic strain relationship of the Xiajia continental loess conforms to the Hardin-Drnevich hyperbola;the overall relationship between it and the influencing factors is as follows:when the same dynamic shear strain is produced,the confining pressure and the solid The greater the junction ratio and loading frequency,the greater the required dynamic shear stress;the greater the water content,the smaller the required dynamic shear stress;(2)The dynamic shear modulus G_d of the loess in the Xiajia mainland area shows a decreasing trend with the increase of the dynamic shear strain?_d.The relationship between the two can be fitted with a logarithmic function;water content,confining pressure,Consolidation stress ratio and loading frequency both have a certain effect on the dynamic shear modulus G_dand initial dynamic shear modulus G₀of loess.The performance is as follows:Under the same dynamic shear strain,G_d and G₀ are both proportional to the water content.Increases and decreases with the increase of confining pressure,consolidation ratio and loading frequency;by comparing the normalized G_d/G₀-?_drelationship curve,it is found that:each influencing factor has an effect on the dynamic shear of loess.The degree of influence of shear modulus is in order:moisture content>consolidation ratio>confining pressure>loading frequency;(3)The damping ratio?of loess in this area increases with the increase of dynamic shear strain.The fitting result of the relationship curve conforms to the logarithmic function,and the value is mainly distributed between 0-0.25;the relationship with various influencing factors It shows an increasing trend with the increase of the moisture content of the loess sample,and a decreasing trend with the increase of the loading frequency and the consolidation stress ratio,and the change with the confining pressure is not obvious;(4)The dynamic strength of loess is affected by water content,confining pressure,consolidation stress ratio and loading frequency.The main performance is:dynamic strength increases with the increase of confining pressure,consolidation ratio and loading frequency;the influence of each test condition on the dynamic strength parameters is the same as that on the dynamic strength;(5)By observing the SEM pictures of the loess in the Xiajia mainland area under different vibration forces,it can be seen that with the increase of the vibration force,the compression force between the skeleton particles of the loess increases,and the particles become denser and denser.,The aggregate particles are also cemented to form larger aggregates under the influence of the squeezing force,and the contact form between the skeleton particles is more converted from point contact to surface contact,and the content of the binder phase between the particles increases,and more Welding connection appears;and the area of the pores is also decreasing,the large pores are more compressed and deformed,and many small pores are split;(6)Through calculation and comparison of the quantitative parameters of loess under different test conditions,it is found that the probability entropy,average shape coefficient,fractal dimension,porosity,sorting coefficient,porosity distribution fractal dimension,etc.will have their own differences depending on the influence factors.The law of change.(7)Taking the dynamic characteristics of loess as a reference series and microstructure parameters as a comparison series,using the grey relational analysis method to further explore the relationship between the dynamic characteristics and the microstructure parameters to determine the degree of influence of each parameter on the dynamic parameters,and to fit the function curve between the two through a polynomial to obtain a quantitative relationship.