During subway operation period

the soft soil foundation is subjected to periodic vibration and intermittent loading

and changes of mechanical properties of soft soil during intermittency will affect its stiffness degradation

which has been ignored in most related previous researches. Hence

considering different dynamic stress ratios and unit intermittent and vibration durations

triaxial tests of undrained continuous and intermittent cyclic loading were designed

where samples were consolidated by real K0

and the long-term stiffness softening rule of undisturbed soft clay under train discontinuous load was studied. Then by comparing the test results of continuous and intermittent loading

it was found that intermittent had a weakening effect on stiffness degradation

which can reduce the residual softening index under large cycle number and shorten the cycle number during rapid softening period. Finally

based on the test results

the influence mechanism of intermittent was analyzed. It was found that soft soil was affected by the excitation during initial loading

and the dynamic adjustment of the soil structure was retained to the intermittency period

which led to continuous pore water pressure generation

stiffness degradation of soft soil

and increase of the average softening rate. After a certain number of cycles

because of the structure adjustment of the soft soil under intermittent and vibration loading in the earlier stage

the soil structure entered the steady state in advance

partial pore water pressure was dissipated

and stiffness loss was restored

which led to the decrease of softening rate in the next vibration. The restored stiffness during the intermittencies was accumulated as the vibration times increased

and the final residual softening index was significantly increased. Under the same conditions

with longer intermittent duration

the initial softening rate was greater

and the attenuation of the softening rate was more significant with the increase of the vibration times

so the weakening of the overall softening degree was more obvious

and the vibration times required to enter the softening stationary phase was fewer.