Analysis Of Long-term Settlement Of Soft Soil Subgrade Under Cyclic Load

Soft clay ground is widely distributed in coastal areas of China.To cope with urban traffic pressure,more and more roads are built on soft ground due to space constraints.Researchs on the long-term settlement of such ground under traffic load is still in development stage,there are two main methods among them which can describe the cumulative deformation process of sof clay: finite element method based on dynamic constituitive model and empirical fitting formula method.However,because of the complex computational procedure and high application cost,the first method is much less used in engineering practice than the latter.Nevertheless,most existing studies do not consider the effect of initial consolidation degree and cyclic stress ratio in the cumulative deformation process.In his paper,a softening index model which considering these two factors is introduced and the following work is completed:Firstly,the constitutive model and the empirical formula model which can describe the deformation characteristics of soft clay are summarized.By analyzing 15 groups data of cyclic triaixal test,the main influence factors of soil accumulation deformation are summarized.Therefore,an improved softening index model considering the initial consolidation degree and cyclic stress ratio is introduced,and then the parameters are obtained by fitting the test data.Based on the secondary development function of ABAQUS,the stiffness attenuation model is embedded into the user subroutine.Compared with the measured data of the Fourth Teaching Road in Hangzhou,the reliability and rationality of the stiffness attenuation model are proved.On this basis,12 groups of comparison models were established based on ABAQUS numerical platform,the influence of the thickness of sand cushion,the stiffness of pavement structure layer and the initial stiffness and Poisson’s ratio of soft clay on road settlement under traffic load is analyzed respectively.Finally,to explore the long-term settlement pattern of soft soil ground after treatment,a finite element model of a unit body of CFG pile composite foundation was established.To verify the rationality of the model construction,the calculated settlement under multi-stage static load is compared with the analytical solution,and measured value.Considering the mechanical properties of soil between piles are not improved,the stiffness attenuation model is applied to describe the constitutive relation of soil between piles.After then,the long-term settlement of composite foundation under traffic load is predicted.