Sonic echo and impulse response tests for length evaluation of soil nails in various bonding mediums

The objective of this paper is to present the results of research for evaluating the installed lengths of soil nails with nondestructive testing methods. Two closely related methods, the sonic echo test and the impulse response test, both of which had been widely applied to assess the integrity of drilled shafts and driven piles, were evaluated to test their capabilities on soil nails. To carry out this study, soil nails of various lengths were embedded in different surrounding materials in the laboratory and then tested with both methods to predict their lengths. The surrounding materials studied in this research included soil and cement grout. Finally, field tests for in situ soil nails were carried out. The results indicated that the relative stiffness of the soil nail to the bond material plays a very important role in the success of testing. It is hoped that through this kind of study, the capability and limitation of using these nondestructive testing techniques to determine the installed lengths or to evaluate the bonding conditions of soil nails can be better understood.