Condition Assessment of Buried Metal-Tensioned Elements

Application of nondestructive test (NDT) methods to assess the condition of metal-tensioned elements in geotechnical engineering applications, including rock bolts, ground anchors, and soil nails, is described. Electrochemical tests, such as measurements of half-cell potential and polarization, were used to detect the presence of corrosion and to evaluate the integrity of corrosion protection systems. Mechanical wave propagation techniques, such as impact and ultrasonic tests, were used to locate features along the length of an element including loss of cross section from corrosion. Interpretation of test results requires knowledge of the electrical continuity between elements being tested and of the details of the installation of the system being evaluated. The utility of the NDTs was evaluated under controlled conditions on bench scale specimens in the laboratory and on buried specimens at a specially developed in situ test facility. However, given the numerous variables inherent to field installations that may have an effect on the measurements, the performance of the NDT technologies needed to be studied in the field. Results from condition assessment employing NDT technologies of tiebacks for a quay wall in Buffalo, New York, and rock bolts along a highway cut in Dresden, New York, are described. Background information is given for each site, including a description of the aggressiveness of the environment relative to corrosion in terms of results from chemical analysis of native soil samples. Results from NDT correlated well with features of the tieback and rock bolt installations. Electrochemical test results indicated that corrosion was occurring, but the wave propagation tests did not indicate any significant loss of cross section. NDT measurements should be archived to serve as a baseline against which future NDT results may be compared.