Nondestructive integrity evaluation of soil nails using longitudinal waves

Structural failures of soil-nailed structures occasionally occur due to the poor integrity of soil nails. The objective of this study was to evaluate soil nail integrity by estimating the installed length and grouted ratio of the soil nails using longitudinal waves. Laboratory experiments were performed using steel bars as well as partially and fully grouted steel bars with different lengths. Field experiments were conducted for in situ soil nails in slopes. The generation and measurement of longitudinal waves were achieved using a hammer and an accelerometer, respectively. The results showed that the velocity of the longitudinal wave along the grouted steel bars in air was the same as that of the grouted steel bars in soil and was less than that of steel bars. The longitudinal wave velocity along the grouted steel bar decreased with an increase in the grouted ratio. The installed lengths of in situ soil nails were evaluated on the basis of the longitudinal wave velocity along the fully grouted steel bar. The results of this study suggest that the relationship between the velocity and the grouted ratio can be a useful indicator for evaluating the integrity of soil nails with different lengths and those connected by the coupler.