Abstract:The pile-soil interaction-damping coefficient with low strain is a key parameter to quantitatively analyze defects of piles. The pile-soil interaction equation was established to determine the damping coefficient using experiments. The time-history velocity at pile top was analyzed corresponding to different damping coefficients and free-end boundary condition. The relationship between the incident and reflected velocity amplitudes ratio at the pile top and the coefficient was developed. Six types of soils were selected to conduct pile-soil interaction model tests and determine the coefficient for different effective overburden pressures,unsaturated and saturated states. Effects of soils and the effective overburden pressure on the coefficient were researched. The experimental results show:(1) the exponential relationship can be used to describe the increment of coefficients with the effective overburden pressure for six soils,but determining coefficients in the relationship are different for different soils;(2) damping coefficients of saturated sands and silts decrease 25% to 60% compared with the coefficients of unsaturated sands and silts. If the effective overburden pressure varied from 85 kPa to 850 kPa,the damping coefficient of the saturated silty clay increased from 250 s-1 to 890 s-1. However,if the effective overburden pressure varied from 20 kPa to 150 kPa,the damping coefficient of the saturated soft clay will increase from 330 s-1 to 420 s-1. The test results were also compared with damping coefficients determined using other methods to show the necessity of determining damping coefficients using the model test method.