There exists critical cyclic stress ratio Sthwhen lightweight sand-EPS beads soil（LSES） is subjected to cyclic loading.Sthis defined as the largest value of cyclic stress ratios corresponding to the flat δ～N curve δ is degradation coefficient of secant elastic modulus and N is cyclic number).Meanwhile Sthis considered as the threshold index differentiating two structural states

i.e.stabilization and failure.Based on the cyclic triaxial test data

confining pressure（σc）

cement content（CC） and EPS beads content（Ve/Vs） are found to be the main factors affecting the value of Sth.Generally

increasing CC

decreasing σcand Ve/Vs can improve the value of Sth.However

under confining pressure of 200 kPa

specimen dt143 exhibits some distinct behaviors due to restructuring.