Stiffness Degradation and Deformation Characteristics of Soft Clay Foundation Under the Train Loads

The hollow cylinder apparatus was used to simulate the stress paths induced in traffic-affected ground, a series of undrained shear tests were carried out. The inflection points on generalized shear strain curves were used to establish a damage criterion, which distinguished different damage characteristics under different stress levels. And the different deformation models can be concluded into three categories which are stable, critical, and destructive, respectively. Groups of tests were carried out to understand the effect of different initial deviator stress on soil shear stiffness, and analyze the variation of shear modulus with vibration times under different dynamic stress ratios. It is found that when dynamic stress level is low, the amplitude ratio a has little effect on the shear stiffness. When dynamic stress ratio level is high, for critical models, the rate of stiffness degradation increases with the increases of amplitude ratio a; for destructive models, the initial shear modulus increases with the increase of amplitude ratio a, soil structure is damaged, its stiffness degrades obviously with increase of vibrations. A prediction model was established for investigating the stiffness degradation pattern when initial deviator stress equals to zero, which provides theoretical supports for the future research on bearing capacity of soft clay foundations that are suffering from repetitive traffic loads.