Abstract:Particle size distribution of the soil has been widely used to evaluate soil properties, and soil particle size distribution curve is affected by soil pretreatments. In order to quantitatively evaluate the influence of sodium hexametaphosphate concentration and ultrasonic vibration time on soil particle size distribution in soil sample pretreatments, a quantitative index representing particle size distribution was selected for t-test. The results show that the fractal dimension can be used as a quantitative index to characterize the dispersion effect of the soil; the dispersion effect of sodium hexametaphosphate reaches the maximum at the mass concentration of 2%, and decreases significantly when the concentration of sodium hexametaphosphate reaches 12%; the dispersion effect of ultrasonic vibration exhibits the turbulence, in which dispersion and flocculation alternate along with time; the optimal dispersion of ultrasonic shock varies with the soil texture, the silty clay with the highest content of grain group (0.25-0.5mm) is dispersed first, followed by the silt and red clay.It is concluded that the dispersion effect of sodium hexametaphosphate is affected by its concentration, and the use of ultrasound alone as a means of dispersion is unreliable.