IN-SITU TESTS USING CRACK-DETECTOR WITH ROTATING PROBES FOR MEASURING SONIC VELOCITY (2ND REPORT) - STUDIES ON CRACK DISTRIBUTION AND SONIC VELOCITY CHANGE IN ROCKS (3RD REPORT).

A crack detector has been developed for measuring the distribution of open cracks and the change in sonic velocity in rock masses. In-site measurements have been performed in a tunnel and a quarry. In order to confirm what part of a retaining wall was damaged by an earthquake, the distribution of open cracks and the change in sonic velocity were measured in a borehole drilled in the retaining wall. From the results of measurement, it was clear that the crack zone in the retaining wall lies on the extension of the boundary between the natural ground and the bank. These findings show that use of the crack detector is practical when the distribution of open cracks corresponds to the undetectable area of measurements for the design of rock and concrete structures.