12.07.2015 Views

Technical Manual: Conduits through Embankment Dams (FEMA 484)

Technical Manual: Conduits through Embankment Dams (FEMA 484)

Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Chapter 10Evaluation by Geophysical and NondestructiveTestingGeophysical and nondestructive testing (NDT) techniques can be used to investigatethe condition of a conduit directly or indirectly by providing data on the condition ofthe conduit and the surrounding embankment dam. These techniques are used todetect flaws, defects, deterioration, and other anomalies that could lead to a failureand do not disturb the feature being evaluated or tested. The most commontechniques used include:• Seismic tomography• Self potential (SP)• Electrical resistivity• Ground-penetrating radar (GPR)• Sonar• Ultrasonic pulse echo and ultrasonic velocity• Mechanical and sonic caliper• Radiography• Surface hardnessDepending on the particular situation, some techniques are more effective thanothers. The selection of the applicable technique(s) requires evaluation of the typeof information needed, the size and the nature of the project, the conditions existingat the site, and any impacts that may result to the structure from performing thetechnique. These techniques require trained and experienced personnel to performand interpret the results. The various applications for these techniques aresummarized in table 10.1. The following sections briefly discuss these techniques.245

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