P-Wave Reflection Imaging of a Cast-in-Steel-Shell Bridge Foundation

An ultrasonic p-wave reflection imaging system was developed to characterize the geometry of vertically embedded structural elements in soils. The components of the system, including the custom transducer probe, associated electronics, and data acquisition hardware, were designed for implementation on the nees@UCLA cone penetration testing (CPT) truck. An overview of the system components and data acquisition is presented, followed by discussion of specific components and their roles in the generation and acquisition of p-waves in soils. The cone penetrometer p-wave system was utilized in a field testing program to image the vertical profile of a cast-in-steel-shell (CISS) deep foundation at an existing suspension bridge in northern California. Characteristics of the CISS foundation and the soil conditions at the site are summarized. The ultrasound probe was pushed alongside the embedded CISS foundation and p-waves were generated at a constant interval with depth. The recorded p-wave reflections were plotted next to each other and the voltage values were mapped to pixel shades to construct an image. The ultrasound probe recorded p-wave reflections from the CISS foundation in the soft, saturated clay at the site, but did not produce returns in stiffer soil layers. The results demonstrate the potential of the system for nondestructive evaluation of deep foundations utilized in transportation infrastructure.