In dynamic triaxial tests,if a soil sample undergoes symmetric sine loading in addition to static deviator stress and if the lateral stress is greater than the axial stress,the sample will assume an axial compressive state when the loading is positive and will change to an equivalent tensile state when the loading is negative.This kind of loading is defined as equivalent tension and compression loading in this study To study the elastoplastic deformation (EPD) of saturated silty clay under equivalent-tension-and-compression loading,we design and perform some undrained dynamic triaxial tests.To consider axial static deviator stress,we apply several levels of sine loading.We determine relations among EPD and confining pressure,static deviator stress,dynamic deviator stress,and compaction coefficients.Furthermore,we propose the tension-and-compression-effect coefficient (TCEC) to forecast the plastic accumulative strain development trend.Test results show that the TCEC is a critical value when considering positive axial compression.When the actual TCEC value is larger than a critical value,the plastic accumulative strain will negatively increase; otherwise,it will positively increase or remain unchanged.Meanwhile,we prove the Hardin model to be an ideal model for reflecting the relation between the dynamic elastic modulus and dynamic strain.The dynamic elastic modulus is typically small when the plastic accumulative strain negatively increases.