AbstractThe cyclic behaviors of soils in the plane strain state have rarely been studied in laboratory tests, while the plane strain hypothesis may have applications on the traffic-induced cyclic properties of subgrade soils beneath long road embankments. To explore the traffic-induced deformation behavior of saturated clays in the plane strain state, and to find its differences from that in the three-dimensional stress state, 55 one-way cyclic tests with compressive loading waveforms were carried out based on a true triaxial apparatus. In the plane strain state, the deformation of the sample in the direction of intermediate principal stress was precluded when the cyclic major principal stress was applied. In the three-dimensional stress state, the deformations were free in all directions, while a combination of major and intermediate principal stresses was cycled. A parameter of bcyc named the coefficient of cyclic intermediate principal stress was introduced to represent the relative relation between cyclic major and intermediate principal stresses. Test results show that both the permanent major principal strain and resilient modulus in the plane strain state were located between the cases of bcyc=0 and bcyc=0.4 in the three-dimensional stress state, and the differences between the two states are aggravated by both the increase of the cyclic stress ratio (CSR) and overconsolidation ratio (OCR). The cyclic behavior of saturated clays in the plane strain state is strongly related to the evolution of bcyc, which is increased by the increase of both the CSR and OCR and may have an upper boundary if the OCR and CSR get large enough. In addition, the shakedown behavior of saturated clays in the plane strain state is analyzed, and the boundary cyclic stress level separating the unstable and metastable ranges is determined.