Acoustic resonance characteristics of rock and concrete containing fractures

In recent years, acoustic resonance has drawn great attention as a quantitative tool for characterizing properties of materials and detecting defects in both engineering and geological materials. In quasi-brittle materials such as rock and concrete, inherent fractures have a significant influence on their mechanical and hydraulic properties. Most of these fractures are partially open, providing internal boundaries that are visible to propagating seismic waves. Acoustic resonance occurs as a result of constructive and destructive interferences of propagating waves. Therefore the geometrical and mechanical properties of the fracture are also interrogated by the acoustic resonance characteristics of materials.; The objective of this dissertation is to understand the acoustic resonance characteristics of fractured rock and concrete. Chapter 2 and 3 show that the spatial distribution and the elastic and viscoelastic properties of fractures in one-dimensional systems have a significant effect on their resonance frequencies and the attenuation. A numerical code that simulates the resonance of three-dimensional bodies containing fractures is developed in Chapter 4 and used to determine the anisotropic elastic moduli of rocks (Chapter 5) and the stiffness of a fracture in concrete (Chapter 6) from measured resonance frequencies. In Chapter 7, the dynamic stiffnesses of concrete bridge columns are determined from their resonance frequencies and good agreement with the changes in the static stiffness is found. Chapter 8 shows that a sheared fracture converts a part of normally incident P-waves to polarized S-waves and vise versa, which can be used as a powerful tool for detecting and measuring shear stress on fractures. A sheared fracture is also shown to have a significant effect on the velocity and particle motion of the waves propagating along the fracture (Chapter 9). Chapter 10 unifies the effects of dynamic coupling (dilation) of a sheared fracture and wave propagation and resonance in an infinite series of multiple parallel fractures in a dispersion equation for anisotropic frequency-dependent wave propagation. This equation provides complete solutions for elastic wave propagation in the media which includes such wave phenomena as generalized Rayleigh-Lamb plate waves, fracture interface waves, and acoustic resonances.