Natural sands are not clean but contain some fines of silt or clay size.In this study

a series of bender element tests has been carried out on mixtures of clean quartz sand and crushed silica fines of different mass contents

covering a range of confining stresses and void ratios.Discussions were made with focus on the influences of excitation frequency and fines content on the output signals.A reliable measure of the first arrival time of shear wave was achieved.It is found that（1）at low excitation frequency the near field effect is prominent for silty sand.On the other hand

the first-kind P wave appears at high excitation frequency

whose amplification is of great dependence on the fines content.Accordingly

the shear wave velocity can be calculated using the first arrival in the time domain;（2）when the fines content increases from 0 to 30%

the shear wave velocity decreases progressively under otherwise similar conditions;（3）a unified model based on critical state soil mechanics is superior to the conventional method in characterizing the influence of various factors.