In engineering practices

the vertical stress and horizontal stress in the subgrade soil unit constantly change

and the amplitude and direction of shear stress also constantly change

which lead to continuous rotation of the stress path in the soil. To investigate the influence of the confining pressure and the cyclic stress ratio(CSR) on strength

cumulative strain

resilient strain and softening of natural soft clay when the principal stress axis continuously rotates under pure axial compression of traffic load

the GDS hollow cylinder apparatus (HCA) is used to simulate the stress path under a laboratory-simulated traffic load

and tests of continuous rotation of the principal stress axis under different confining pressures and different cyclic stress ratios are carried out. The testing results show that with the accumulation of pore pressure

the samples of natural saturated soft clay gradually softened. The axial and torsional moduli decreased with increasing CSR and confining pressure and then reached a steady value after a certain number of cycles. When the cyclic stress ratio was relatively small

the axial and torsional stress-strain hysteretic curves were linear

and almost coincided with different cycles. With the increase of the number of revolving cycles of the principal stress axis

the axial and shear stress-strain hysteresis curves became more and more nonlinear. The axial and shear stress-strain hysteresis loops of the specimens no longer coincided with the rotating circles

and the hysteresis loops gradually tilted towards the x axis. With the increase of cyclic stress ratio

the axial and shear moduli quickly attenuated at the initial stage of loading and then reached a steady value. Moreover

when the axial and shear moduli of the specimen were stable

the corresponding number of revolving cycles of the principal stress axis increased with increasing confining pressure and cyclic stress ratio.