| The purpose of this study was to develop a novel nondestructive testing technique, Acoustic Travel Time Tomography (ATTT), that will improve our ability to evaluate large concrete dams. Until the development of ATTT, no nondestructive test method existed that could determine the location and extent of cracking within a dam. No other method could determine the modulus of elasticity at a specific location within the dam and determine a global value of the modulus of elasticity for a large section of the dam.; The research program began with an idea, that cracks, weak areas, and other anomalies will slow the velocity of acoustic waves as they travel through a mass concrete dam. This study has taken that concept and combined it with other nondestructive evaluation methods that were developed for shallow seismic surveys, nondestructive testing of concrete structures, and nondestructive evaluation of interfaces. The resulting technology provides a unique method to evaluate large concrete dams. Acoustic Travel Time Tomography was tested in the laboratory, modified for large scale testing, then evaluated for reliability. This dissertation reports the methodology, instrumentation, and data analysis techniques developed for Acoustic Travel Time Tomography.; The research demonstrates that ATTT can locate and characterize cracks, voids and anomalies deep within a mass concrete dam. The results at each stage of the study have shown that Acoustic Travel Time Tomography (ATTT) is a highly accurate testing procedure, and is uniquely well suited for evaluating large concrete dams.; This thesis shows that ATTT is an original contribution to knowledge that, at present, no alternative testing procedures can provide equal or better information about a large concrete dam. |
