Abstract：Research purposes: To study the subgrade deformation characteristics under cyclic loading and identify the dynamic characteristics of embankment，the basic conditions of the test section of the Jiaozhou － Xinyi Railway are introduced in this paper． A theoretical analysis of the relationship between subgrade settlement and time is made and the model for calculation of the subgrade and equation for soil constitutive are given． Through studying the elastic and plastic deformation characteristics of the subgrade under dynamic load，the decay curve of the subgrade dynamic stress is obtained．
Research conclusions: ( 1 ) The practical strain wave propagates within limited depth and its elastic deformation is generally small under 5m of the subgrade ． The proportion of the elastic dynamic strain is small with less than 0． 06% and it decreases with increase of the depth，so the elastic dynamic strain makes little impact on the post － construction settlement of the soft soil subgrade． ( 2 ) After doing the dynamic tests of 1． 5 million times，the subgrade plastic deformation values are as follows: the plastic deformation of graded crushed stone subgrade is 27． 35mm and the loose soft plastic deformation is 2． 67mm． The impact of the dynamic load on post － construction settlement mainly reflects in bedding，and the post － construction settlement is stable after 1 year．
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2011, Vol. 28 
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