Cone Penetration Test-Based Ultrasonic Probe for P-Wave Reflection Imaging of Embedded Objects

An ultrasonic P-wave reflection imaging probe is developed and utilized to noninvasively image the geometry of a deep foundation supporting a bridge pier. The source ultrasonic transducer emits compressive waves into saturated soil that subsequently transmits to and reflects back from an embedded object, and the receiver transducer measures the reflections that are used to construct an image. The components of the system, including the custom transducer probe and data acquisition hardware, were integrated with the nees@UCLA cone penetration testing truck. Some fundamentals of propagation of ultrasonic waves in soil are presented first, including transducer directivity, effects of unsaturation, the size of the internal scale of the soil, and transducer coupling. The system components are then presented, followed by field testing. The probe successfully imaged a pile foundation in very soft saturated clay but not in stiffer and/or unsaturated soils. The probe could be very useful for nondestructive quality assurance of structural elements constructed in situ in soft saturated soils.