The highway guard rail barrier is a critical part of the highway safety features. Chinese design standards provide specific requirements on the embedding depth of guard rail posts. However, contractors in isolated cases shortened the embedding depth under unfavorable ground conditions. Such shortened rail posts can not be relied upon to ensure the safety of freeway traffic. Until recently, pulling out a post was the only method to inspect the embedding depth. Due to its high cost and destructive nature, the pull-out testing is unsuitable for routine inspection purposes. The primary goal of this study is to develop a fast and reliable alternative testing method suitable for such purposes. The principles of the new method are similar to those used in evaluating the integrity of foundation piles. Basically, a pulse signal is introduced at the pile head that travels downward and reflects at the bottom section. The initial and reflected signals are then extracted and used to deduce the length of the pile. However, this method is normally considered not suitable for testing hallow piles due to rapid attenuation, excessive noise and free vibration. In this study, the authors developed a number of innovative techniques including automated agitation, free vibration elimination software, reflection wave extraction, enhancement and analysis method, high-precision spectral analysis, and an intelligent post length evaluation system. This new technology has been successfully verified in multiple highway construction projects in China. The pilot testing program concluded that both the efficiency and accuracy of the new method are satisfactory for engineering practice purposes.
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