Electromagnetic Launching System as an Alternative to Non-Destructive Sonic Wave Generation for Steel Bar Length Determination

Soil nailing system is widely used along highways in Brazil. Non-destructive techniques have been used to estimate the length of installed soil nails. Sonic Echo and Impulse Response techniques evaluate the bar length using sonic wave propagation. The methods are similar and consists in generate an impact with a hammer. Results may be affected by this non-standard procedure. This paper aims to propose an automated sound wave generation in order to carried out tests quickly, with reproducibility and without operator dependence. An electromagnetic launching system was developed, which uses a projectile in place of the hammer, and the electromagnetic force instead of human force. The sound data was received by a microphone and sent to the computer by a microcontroller, making the system compact and portable. Projectile output speed optimization and impact reproducibility were analyzed. Nails length were obtained by both time and frequency domain data analysis. Results showed high reproducibility under the same initial condition. Propagation velocity presented a relative error less than 1% for steel bar with length of 1 m.