Research On The Effect Of Loess Stress-strain Relationship And Strength Parameters Under Seismic Loading Disturbance

With the deep develop of the western development stategy, in recent years the scale of capital construction gradually expand over The Loess Plateau, coupled with the impact of agricultural irrigation, rainfall, earthquake and other factors, loess landslide occurrence frequency increasing. The earthquake caused rock and soil of the slope damage, loose and cracking, it is extremely easy to initiate new landslide by rainfall and other factors after the earthquake, which has been confirmed by the phenomenon of frequent occurrence collapse, landslide, debris flow and other disasters after the Wenchuan earthquake in 2008 5.12. Many areas of the Loess Plateau are in high intensity seismic region, there are also occurred some strong earthquake in history like Hua County earthquake and Haiyuan earthquake etc. So research the damage and deterioration of the loess strength and deformation properties after vibration load disturbance, is crucial to analyse loess landslide of post earthquake secondary disaster risk and take corresponding measures for disaster prevention and mitigation. The paper take Xi’an loess as the object for the research, use simplified cyclic vertical load from vibration table to simulate seismic loading to test on undisturbed loess, based the achievements of the seniors, and through the theoretic derivations and experimental analysis works some achievements which have certain theoretical reference value and actual significance are obtained.Aiming at the characteristics of cementation,macrostructure of undisturbed loess is easily arises structural damage and the strength reduction under the cyclic loading. Use cyclic vertical load from vibration table to simulate seismic loading, by control two of the disturbance frequency, displacement amplitude, vibrate duration constant and change another parameter respectively, and searched the changes about stress-strain relationship, volume change, matric suction, and shear strength parameter of each disturbed state under unsaturated triaxial test, discussed the effect and relationship between each parameter and strength and deformation of loess. The test results show that the change of the disturbance frequency, displacement amplitude, vibrate duration have different effects on the loess structural damage:(1) with the increase of each parameter suction will decrease no matter the initial suction or at the end of shearing;(2) The parameters have little effect on the residual strength and stress-strain relationship after soil sample destroy;(3) Influence of frequency change on the cohesion and the yield strain of loess is a power function form, the influence of the peak deviator stress is logarithmic function form, showing a trend of linear effect on the angle of internal friction;(4) Changes of the displacement amplitude have a logarithmic function form to the peak deviator stress of loess, influence of the yield strain, the cohesion and angle of internal friction is a power function form;(5) Influence of vibrate duration to stress-strain relationship and shear strength parameter all showing a linear trend. The paper will provide reference for further research of ground motion parameters influence on the mechanical properties of loess and for the macro analysis of post-earthquake secondary disaster safety and slope stability.