Abstract: Test data show that dynamic deformation characteristics of Shanghai soft soils are consistent with law of strain softening; and they can be described by Davidenkov model well. Firstly, based on Davidenkov skeleton curve, the dynamic shear stress-strain curves for loading and unloading are constituted by Masing rules; and the equations of incremental tangent shear modulus of skeleton curve and hysteresis curves are derived. Then the dynamic stress-strain relation is extended from one-dimensional to three-dimensional strain space. Using the development platform of FLAC3D, the nonlinear dynamic model of soils is programmed, which is based on Davidenkov skeleton curve and according with generalized Masing rules; and the validity and rationality of the program are validated by a complex stress-strain loading path. Finally, based on the soft soils test data of other related study, the calculated results by the program and test data results of related study, which contain the relation curves of dynamic shear modulus ratio vs. shear strain amplitude and damping ratio D vs. shear strain amplitude , are compared under series of different levels of shear strain amplitude. Study results show that compared with Hardin-Drnevich model which is widely used in engineering, the - curves and D- curves based on the Davidenkov skeleton curve are fitting to the soft soils test results better, so as to prove the rationality and practicability of the proposed constitutive model, and can be used for the dynamic response analysis of soft soils sites in Shanghai.

Key words: nonlinear dynamic constitutive relation, dynamic shear modulus ratio, damping ratio, development of constitutive model, test curves