This paper aims at studying the cyclic softening of strength and stiffness of natural sedimentary structural clay in long-term dynamic loading. The artificial structured soils with different inter-particle bonding strengths and different initial void ratios are prepared

using cement as bonding material and sugar to mimic the large pores. A series of dynamic triaxial tests is performed on the structured clay and corresponding remolded soil to investigate the influence of bonding strength

initial void ratio

confining pressure and dynamic stress amplitude on the accumulated deformation and dynamic strength. Three distinct relationships between accumulative plastic strain and cyclic number can be identified according to the critical cyclic stress ratio(CSR): plastically stable

critical and destructive types. The critical cyclic stress increases with the increase of inter-particle bonding and the decrease of initial void ratio. The structured clay with higher bonding strength behaves in more obvious brittle failure

and has a smaller strain associated with the inflection point of the accumulated strain curve

which is suitable to be regarded as the strain failure criteria for dynamic strength. Moreover

the dynamic strength increases with the increase of inter-particle bonding and the decrease of initial void ratio

and the dynamic cohesion cd decreases with the increment of cyclic failure number; while the dynamic angle of internal friction ?d basically remains unchanged. This study results can provide useful reference for controlling the dynamic catastrophes of soft ground.