Advances in Stress-Wave Nondestructive Testing Methods for Evaluation of Deep Foundations-Paper

Paper

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The paper presents prototype high-resolution stress-wave nondestructive testing (NDT) systems intended to improve quality assurance and quality control of deep foundations. The systems target two gaps in current practice: detecting defects such as corrosion-related section loss in existing piles and shafts, and identifying problematic ground beneath drilled-shaft excavations, including karst features.<br /><br />Two modular ultrasonic systems were tested on large-scale laboratory models. In the in-service foundation model, P-wave reflection imaging detected a steel pipe pile, exposed reinforcing steel, and a void. Estimates of pile section loss were reasonably consistent with the model’s known geometry. The system could identify exposed rebar but could not assess rebar beneath concrete cover.<br /><br />In the karst model, S-wave imaging located several vertical and horizontal soil seams, with estimated positions generally matching their actual locations. However, the deepest anomalies were not detected, indicating inadequate penetration at the transducers’ high operating frequency.<br /><br />The laboratory results demonstrate the potential of stress-wave imaging to improve foundation inspection, including resolving small changes in cross section. However, further development is needed to increase investigation depth, better characterize anomalous zones, and adapt the equipment and methods for practical field use. The authors conclude that continued advances in NDT are important for addressing limitations in current deep-foundation QA/QC practices.

Keywords

stress-wave nondestructive testing

deep foundations

quality assurance

quality control

ultrasonic imaging

pile defects

corrosion-related section loss

karst features

P-wave reflection

S-wave imaging