lnsitu Measurement of Damping of Soils

The Seismic Cone Penetration Test (SCPT) has been shown to give reasonable results for insitu measurements of shear wave velocity, and this paper extends this work to include measurements of damping. The relevant equations of motion are described, factors affecting amplitude decay are discussed, and the nature of damping is summarized. Consideration is given to some of the practical aspects of pre-processing of signals. Three methods of damping calculation are presented. The first two, attenuation coefficient and modified SHAKE methods, require the application of amplitude corrections, which is not straight-forward, give variable results, and indicate negative damping in a clayey silt layer. The third, the spectral slope method eliminates the need for amplitude corrections and gives less variable and more acceptable results. The spectral slope method gave damping measurements of about 2% to 3% for sand and 0.3% to 0.5% for silt, at low strain levels of 10-4 to 10-3%