This paper presents the findings from a research study that evaluated nondestructive test (NOT) methods that may be useful for quality assurance purposes during construction of soil nail retaining walls. More specifically, the new NDT procedure will be used to evaluate the integrity of the grout column surrounding the steel tendon and to measure the grouted length of the installed soil nail. A preliminary evaluation of the existing NDT methodologies was undertaken to identify candidate NDT methods. The selected NDT methods, sonic echo and impact echo, were subjected to a detailed evaluation through three series of full-scale field NDT testing. The findings from the sonic echo tests are presented in this paper. The field studies demonstrated that the sonic echo method can be used successfully to detect major defects in installed soil nails. The nail condition predictions from sonic echo tests were confirmed by actual nail conditions observed after all the soil nails were exhumed.