The Experiment Study On Dynamic Properties Of Unsaturated Loess Under Cyclic Loading

In China, the distribution of loess is particularly influenced by climate andregional characteristics and most loess distributes in the central and westernregions of the country. Because the region is located in the frequent seismicactivity area, under the condition of earthquake and large deformation vibration,loess foundation of buildings and structures and loess slope often have seriousseismic subsidence, landslides and other geological disasters. In this paper, theloess samples from Shenhe highway slope were studied by dynamic triaxial test.The dynamic properties of unsaturated loess samples under the cyclic loading,including natural loess samples and remolded loess samples, with differentconfining pressure, different consolidation stress ratio and different watercontent were researched. And then the law of dynamic constitutive relationshipof the unsaturated loess, dynamic elastic modulus, dynamic damping ratio anddynamic strength were concluded. The main conclusions of this dissertation areas follows:（1）The dynamic stress-strain curve of Shenhe highway unsaturated loessunder the cyclic loading is hyperbola. The fitting degree of natural loessdynamic stress-strain curve to the hyperbolic model is better than that of the remolded loess. By using the method of stepwise loading and single step loading,the dynamic stress-strain curves of loess show differences. Consolidation stressof the loess has an obvious effect on the dynamic stress-strain curve. Under thesame condition of the dynamic strain，dynamic stress of loess increases with theincreasing of confining pressure and consolidation stress ratio. When the watercontents of unsaturated remolded loess samples range in11%to19%, the watercontent has little effect on the dynamic stress-strain relation curve of loess.（2）The dynamic modulus of elasticity of unsaturated loess in Shenhehighway decreases with the increasing of dynamic strain. As dynamic straindeveloped to a certain degree, reduced amplitude of the dynamic modulus ofelasticity of unsaturated loess will decrease. Dynamic modulus of elasticity ofloess increases with increasing of initial confining pressure, consolidation stressratio. The dynamic modulus of elasticity of unsaturated remolded loess increaseswith decreasing of the water content.（3）The dynamic damping ratios of unsaturated natural loess samples fromShenhe highway slope are about0.10to0.25, ratios of remolded loess samplesare about0.05to0.20. The dynamic damping ratios of remolded loess areslightly smaller than that of natural loess. The reason is that in situ structuralcharacteristic of loess has beneficial influence on the strength. According to thedynamic triaxial test, water content, confining pressure, consolidation stress ofunsaturated loess can direct affect the dynamic damping ratio of loess. Dynamicdamping ratio of loess increases with increasing of initial confining pressure, butdecreases with increasing of consolidation stress ratio. Dynamic damping ratioof unsaturated remolded loess increases with increasing of water content.Comparing with the remolded loess, the relationship between dynamic dampingratio and dynamic strain of natural loess has better regularity.（4）The nature of loess, environment of the stress, vibration stress of the loess will directly affect the dynamic strength of unsaturated loess. The testresult of dynamic strength shows: dynamic strength of unsaturated loessdecreases with increasing of vibration frequency and consolidation stress ratio,and increases with increasing of initial consolidation stress. The most directfactor which affects the ability of resistance damage deformation of unsaturatedloess is confining pressure. But after the consolidation stress ratio developed to acertain degree, effect of the direct factor (confining pressure) on the dynamicstrength of unsaturated loess will weaken continuously.（5）Influenced by in situ structuralcharacteristic of unsaturated loess, thelimit dynamic load of natural loess is slightly higher than that of remolded loess.Using the method of stepwise loading to measure the dynamic strength of thenatural loess, the value of result will be higher than the value of single steploading method. So it is unsafe to use these parameters tested by the method ofstepwise loading in foundation engineering and slope design. All the quantitativeparameters of dynamic strength of unsaturated loess will decrease withincreasing of vibration frequency.