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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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<strong>Conduits</strong> <strong>through</strong> <strong>Embankment</strong> <strong>Dams</strong>Figure 144.—GPR profiles along a conduit invert. The large amplitude white-blackreflection patterns are associated with concrete underlain by voids in drill holes (DH)DH-05-01 <strong>through</strong> -03.for generated sonar pulses to return to the transducer (<strong>through</strong> air or water) are afunction of the distance that the pulse travels, it is possible to precisely measure thedistance to the conduit surface. When processed by a computer, thousands of thesemeasurements can be used to generate a map (figure 145) of the condition(deflection, joint size, depth of deterioration, etc.) of the conduit. The precision ofthe system is such that measurements of fractions of an inch can be made. Thesonic velocity can vary with temperature and humidity, and calibration is requiredprior to commencing with the inspection. The accuracy of the measurementsdepends upon the calibration. The sonar can also be used in navigating thetransporting unit within the conduit.Recent improvements in this technology allowed the USACE to investigate thecondition of a conduit without unwatering it. A computer processed signals receivedfrom sensors mounted on an ROV to generate three-dimensional images. The usercan manipulate the images on the screen in real time to change the observationalpoint of view via graphics software. Thus, the graphics software allows the user to254

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