The instability mode and shear behaviour of saturated loess are the basis for analyzing seismic deformation of loess foundation and their structures.To reveal the unique strength attenuation and deformation deterioration of saturated loess under cyclic loads,the dynamic soil strength,development of the pore pressure and instability modes of the saturated loess were investigated by the cyclic triaxial test,subjected to the initial shear stress(qs)and the cyclic shear stress(qc).The experimental results show that:When qs＜qc,the loess samples exhibit the cyclic mobility failure type;When qs≥qc,the reconstituted loess samples exhibit the flow failure type,while the intact loess exhibit the plastic strain accumulation failure type.The cyclic stress ratio(RCS)and the cyclic resistance ratio(RCR,10)of the loess samples increases first and then decreases with the increase of the initial shear stress ratio(RSS).At the initial stage of cyclic loading,the pore pressure in loess samples increases rapidly with the cyclic mobility and plastic strain accumulation failure types,and the pore pressure development curves show the trend of"organ"or"hornt"type.The growth rate of the initial pore pressure in the loess samples with the flow failure type is relatively slow.When the pore pressure reaches a certain cycle,it increases sharply and the pore pressure curve shows a"sickle"type.A chart is established by considering the influence of initial stress state(qs/qc)and the initial pore pressure development index(K1-2),it can be used to predict the failure mode of saturated loess under cyclic loading.
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