Attenuation in soils and non-linear dynamic effects

This research begins with a critical review of attenuation mechanisms in geomaterials, assesses the inherent biases in resonant column testing, addresses attenuation mechanisms in dry sands and in moist sands, and concludes with an study of stochastic resonance in frictional geomaterials (a non-linear dynamic effect).; The magnet-coil system in the resonant column device provides not only the required cyclic excitation but also an induced counter electromotive force that opposes the motion. An electro-mechanical model is developed to quantitatively examine the electromotive effects and to correct the inferred resonant frequency and the damping ratio. The measurement bias is more pronounced on the damping ratio, and the error is a function of the device characteristics and material properties.; Micro-slippage at particle contacts is the most frequently involved mechanism to account for energy loss in dry sands. However, such mechanism is not adequate to explain the non-zero minimum damping ratio D_min at strains below the linear threshold strain. It is proposed that the non-zero D_min arises from internal friction within the material that makes the particles, specially, thermoelastic relaxation.; Experimental evidence demonstrates that adsorbed water layers affect the attenuation in moist sands. At the macro-scale, effects of adsorbed water layers are investigated with resonant column testing and sand specimens at controlled relative humidity. Results show that adsorbed water layers change both the damping ratio and the shear modulus. At the micro-scale, adhesion hysteresis at capillary-bridges between asperities is experimentally evaluated using Atomic Force Microscopy (AFM) and mineral substrates. Experimental results show that adhesion hysteresis develops even at low relative humidity. A mesoscale contact pivoting model is developed to relate the effect of capillary bridge at interacting asperities to average losses at the level of interparticle contacts.; As friction is a non-linear thresholding-type behavior, the potential manifestation of stochastic resonance in the dynamic behavior is explored in this study. Results demonstrate that stochastic resonance takes place in the frictional system with a single interface. While the classical signature of stochastic resonance is not observed in multi-interface systems (i.e. soils), clear non-linear energy coupling effects are manifested.