Effects of Imperfect Fixity in Spring-Top Resonant Column Tests
A two-degree-of-freedom model is proposed to study the effects of imperfect fixity at the active end of the spring-top resonant column apparatus. A computer program using the SYMPHONY spreadsheet is developed to calculate the dimensionless frequency, F, from which the modulus can be determined. It is found that the effect of reaction mass through the parameter, Tr; on dimensionless frequency, F, cannot be ignored if Tr < 20. As the ratio of mass attached to the active end of the specimen to specimen mass, T0, increases, the variation of F increases. When Tr = 20, the effect of T0 becomes small. It is recommended that Tr be greater than 20 if the single-degree-of-freedom model is used to determine modulus of soil. It also is found that damping ratios of specimen and apparatus do not strongly affect the dimensionless frequency, F.