Dynamic Shear Modulus of Soil Using a Random Vibration Method

Abstract

The random vibration method is proposed in this study for evaluation of the dynamic shear modulus of soil using the apparatus developed by Hardin, and the results are compared with that obtained by the standard sinusoidal test.The soil specimen made of two kinds of clay and sand were placed in the triaxial cell, and twisted at the top by sinusoidal or random forces through the magnetic coils under uniform confining pressure and drained condition. The shear modulus of soil by sinusoidal vibration was computed from the resonant frequency of the soil specimen-top cap coupling system, and that by random vibration was from the expected frequency which was deduced from the narrow-band process theory. In this research study, shear strain amplitude was very small (less than 10-5), and the equivalent damping constant of soil was less than 0.05.If the test apparatus-specimen coupling system produces an apparent nonsymmetry in the frequency response function with respect to the resonant frequency, variations in the evaluation of the informations on the response characteristics of the system over a wide range of frequency result creating the inconsistencies in computation of the shear moduli from the random and sinusoidal vibration tests. Larger differences between the shear moduli by both methods are observed at low confining pressures.