By using resonant column apparatus

the dynamic parameters of interbedded soil and other soils in two sites are tested; the curves of dynamic shear modulus ratio G/Gmax and damping ratio versus dynamic shear strain amplitude of the soils in two sites are given. Compared with the variation range of G/Gmax vs. and D vs. curves of other soils

it is obviously that the G/Gmax vs. and D vs. curves of mucky silty clay and fine sand interbedded strata are more close to those of soft clay. By calculating the seismic response of the two sites

the results show that the interbedded soil weakens the peak acceleration greatly and its maximal shear strain amplitude is very big which is near to be failure under horizontal earthquake. The dynamic characteristic of interbedded soil is similar to that of soft soil; and this property is caused by its special conformation

i.e. the feeble horizontal joint planes are overgrown.