Theoretical evaluation of embedded plate-like and solid cylindrical concrete structures with guided waves

The as-built condition of diaphragm walls or pile foundations affects the performance of a structure supported by these elements. A three-dimensional guided wave approach can extend the frequency range to allow detection of smaller size defects in foundations when compared to conventional non-destructive evaluation. The objective of this research is to develop theoretical and numerical solutions of Rayleigh-Lamb waves in embedded plate-like structures (diaphragm walls) and flexural mode waves in embedded solid cylindrical structures (pile foundations). The guide wave theory provides information about group velocity, phase velocity, and attenuation as a function of frequency.; The dispersion relations in a complex-valued matrix form are expressed as transcendental solutions between wave number and frequency for given material properties of concrete and soil. Guided waves are graphically illustrated as dispersion and attenuation curves. Group and phase velocities are derived from the dispersion curves and are functions of frequency.; Results of parametric analyses show that the real part of the dispersion curves is not affected by boundary conditions, concrete-to-soil shear modulus ratio, concrete-to-soil density ratio, and soil type. However, these dispersion curves depend upon the Poisson's ratio of concrete. Attenuation curves are affected by boundary conditions, concrete-to-soil shear modulus ratio, density ratio, and soil type. The theory suggests that the usable frequency ranges for conventional NDT tests, defined as the frequency range where the propagation velocity is constant, are inversely proportional to plate thickness or cylinder diameter.; Normalized displacement distributions are introduced to allow comparison of mode shapes from different orders/branches of the dispersion curves. From a practical viewpoint, the modes or orders/branches with the lowest attenuation, simplest shape, and largest displacement magnitude should be most easily induced and detected in guided wave experiments. The positions of the maximum relative amplitude of the normalized displacements are suggested as the best locations to install transducers for testing.; The guided wave theory was applied to experimental results of impact echo methods on concrete walls. The theory can identify resonant frequencies not identified based on one-dimensional wave theory interpretations. Recommendations are presented for selecting modes to be used in guided wave experiments in embedded concrete cylinders.