With the GDS dynamic triaxial system

undrained dynamic triaxial tests on the saturated sand of different fines contents were performed; and effects of fines content on the dynamic elastic modulus and damping ratio were analyzed. Results show that the dynamic elastic modulus of sand decreases with increasing of fines content; but the trend is reversed beyond the critical value of fines content of 30%. The damping ratio of sand firstly increases and then decreases with increasing fines content at the same critical value of fines content of 30%. When fines content is less than 30%

the dynamic characteristics of sand is determined mainly by the coarse grains; the skeleton void ratio between coarse grains increases with the increase of fines content; and the ability to resist deformation under the same strain level weakens so that the elastic modulus decreases. Meanwhile

the stress wave propagation speed slows down because of the reduction of contact points between soil particles

hysteresis quality of the soil dynamic load response strengthens and the damping ratio increases; when the fines content is greater than 30%

the dynamic characteristics of sand is determined mainly by the fine grains; the interfine void ratio decreases with increasing of fines content; so that the dynamic properties of sand shows a reverse trend.