Laboratory Development of a Borehole Nondestructive Testing System to Evaluate Embedded Foundation Elements Using Stress Waves

摘要

A borehole nondestructive testing (NDT) system was developed to create high-resolution reflection images of foundation elements for the purpose of evaluating integrity and embedment length. The system is deployed inside a borehole and functions by generating stress wave reflection signals from a foundation element. Surface NDT methods that have been developed for integrity/length applications often suffer from limitations related to data interpretation and energy transfer, particularly for more complex foundations such as pile groups. The system used in this study was developed for foundation evaluation purposes (based on a previous cone penetrometer probe design) and subjected to laboratory testing to ensure compatibility with foundation testing constraints. A summary of hardware components and system operation is presented as well as the results from laboratory testing on a large soil model. The soil model was developed with reduced-scale embedded deep foundation elements to evaluate system performance with regard to integrity testing and length estimation. The system was capable of differentiating between competent and anomalous sections of the tested foundation element. A reliable estimate for foundation length was also obtained. Recommendations for refining the system are also discussed based on the results from laboratory testing and anticipated future field-testing conditions. nondestructive testing; deep foundations; defects; unknown foundations; ultrasound; P-waves