Abstract：Through analyzing the test results of free vibration column apparatus on recently deposited soils of flood plain including clay，silty clay，mucky silty clay，silty clay and fine sand interbedded strata，silt and fine sand in Nanjing and its neighboring areas，the effect of confining pressure，shear strain and soil structure property on dynamic shear modulus G and damping ratio l is investigated in detail. The confining pressure has a significant influence on the dynamic shear modulus ratio. The more the effective confining pressure increases，the less the dynamic shear modulus ratio G/Gmax reduces with shear strain increasing. After normalized by Gmax，the values G/Gmax of different confining pressure scatter in a narrow band and their discreteness is small. Compared with the test results of Seed and Idriss for silty clay and fine sand interbedded strata，the value of shear modulus ratio changes between lower boundary of sand and saturated clay curve proposed by Seed and Idriss. Those values are close to lower boundary of sand and keep away from Seed-Idriss saturated clay curve，so it may be concluded that the dynamic shear modulus of silty clay and fine sand interbedded strata is similar to that of sand. For sand soil and silty sand including mucky silty clay，the value of damping ratio approaches the lower boundary of sand l-g curve proposed by Seed and Idriss. Damping ratio is smaller than that of sand soil when the shear strain is the same. However，for silty clay and fine sand interbedded strata，the date of damping ratio falls between upper boundary of sand and Seed-Idriss mean curve. So，the damping ratio of silty clay and fine sand interbedded strata is higher than that of general sand. By comparison between the test results and the variation range of G/Gmax-g and l-g curves of sand recommended by Seed and Idriss，it is concluded that the silty clay and fine sand interbedded strata should not be simply treated as sandy soil or silty clay. Based on the test results and theoretical analysis，the average curves，recommended values and envelopes of dynamic shear modulus ratio G/Gmax and damping ratio l versus dynamic strain g for recently deposited soils in Nanjing and its neighboring areas are presented. But the proposed values can only be used as reference because of the complexity of l and. G
