Damping Ratio of Soils from Laboratory and in Situ Tests

This paper considers the influence of N and g' on the damping ratio (D) of two undisturbed Italian clays and of three reconstituted granular soils. The experimental results were obtained in the laboratory by means of a Resonant Column/Torsional Shear apparatus. The damping ratio of a reconstituted silica sand was also determined, at small strains, from seismic tests performed in a large Calibration Chamber. The spectral ratio and the spectral slope methods were used for this purpose. The capability and limits of these methods are discussed in the light of the strong influence of test conditions on damping ratio even at very small strains. Finally the experimentally determined values of D are compared against those predicted by means of simple non-linear models that incorporate the Masing rules.