Study On Over-Consolidation Characteristics Of Saturated Clay Under Cyclic Loading

In recent years,with the rapid development of social economy and rapid growth of population in China,the level of urbanization has been constantly improved,but the urban road transportation network is unable to meet the current demand.Under the condition of limited land resources,people turn their eyes to underground,and subway becomes the main way to solve people’s travel problems.During subway operation,due to the soil bearing the cyclic dynamic load from the subway,the consolidation state of the soil will change,which is generally manifested as the softening strength and stiffness of the soil layer,resulting in the uneven settlement of the stratum,which will seriously affect the normal use of the subway and cause major safety accidents.Therefore,it is very important to study soil properties under cyclic dynamic load.On the basis of previous studies,I carried out researches on the overconsolidation characteristics of saturated clay under cyclic load,mainly starting from dynamic triaxial test,soil constitutive model theoretical research,etc.,and systematically studied the overconsolidation characteristics of saturated clay under cyclic load,the main research content includes the following aspects:(1)Using GDS dynamic triaxial apparatus to carry out the static shear test of saturated clay,overconsolidation ratio and consolidation pressure is discussed the influence of the static shear characteristics of saturated clay,summarizes the normal consolidated soil and over-consolidated soil of the difference between static shear properties,determine the applicable saturated clay yield criteria to judge and phase transformation,according to the yield point summed up the applicable to the alpha yield surface model of saturated clay under static load,summed up the applicable safety damage strength formula of saturated clay under static load.(2)Cyclic dynamic load test and static shear test of saturated clay were carried out by using GDS dynamic triaxial apparatus,and the effects of cyclic load amplitude,cyclic loading times,quasi-overconsolidation ratio and consolidation pressure on the bearing characteristics of saturated clay were considered.The relation curve of strain/pore pressure and number of cycles in the cyclic stage is analyzed,and the key factors affecting the dynamic characteristics of saturated clay are summarized.To explore the effect of the hysteresis of pore pressure caused by experimental conditions on the static shear characteristics of saturated clay.(3)Conduct in-depth analysis on the stiffness softening of saturated clay,analyze the hysteretic curve of quasi-overconsolidated soil,introduce the softening coefficient,establish the relationship between the softening coefficient and pore pressure/strain,and put forward the stiffness softening model suitable for saturated clay.(4)In this paper,the difference of characteristics of overconsolidated soils caused by static and dynamic cycles is explored,and the yield surface model of overconsolidated soils and quasi-overconsolidated soils is summarized.Based on theoretical analysis,the formulas of safety failure strength of overconsolidated soil and quasi-overconsolidated soil are put forward,whose significance is to provide a certain safety reserve for the strength of rock and soil under normal use conditions,so as to reach the critical failure strength early warning for soil,improve the safety of the project,and reduce the occurrence of engineering accidents.