Laboratory and in-situ measurement of attenuation in soils

Abstract

Attenuation in wave propagation in soils is the decay of the wave amplitude. Total attenuation arises from geometric spreading, apparent attenuation, and material losses (intrinsic attenuation). Intrinsic attenuation is typically quantified in terms of the damping ratio, D. In laboratory tests, the damping ratio measurement is in general implemented under quasi-static and resonant conditions. Under both conditions, only material losses are reflected in the measured total attenuation. It should be noted that damping ratios measured by different techniques taken under various frequencies may not be comparable if the damping ratio is viscous in nature. For in-situ testing, corrections for geometric spreading and apparent attenuation are required to obtain the material damping ratio. The spectral ratio method is an effective way to make such corrections. Preliminary studies conducted in a K-o-container in the laboratory show that the measured damping ratio by the spectral ratio method (D-min similar to 4%) is much higher than the measured ratio by the resonant column test (D-min similar to 0.23%), although the coupling effects including the transducer response are considered. This discrepancy may be due to interference of the sensor with the propagating wave, multiple reflections from the boundary, near field effects, phase delay and signal distortion from the peripheral electronic devices, and other unknown factors.