Application of P-wave Reflection Imaging to Unknown Bridge Foundations and Comparison with Other Non-Destructive Test Methods

Abstract

Proper design of bridge structures requires an appreciation for the possible failure mechanisms that can develop over the lifetime of the bridge, many of which are related to natural hazards. For example, scour is one of the most common causes of bridge failures. Scour occurs due to the erosion of soil and sediment within a channel with flowing water. During a flood event, the extent of scour can be so great that it can destabilize an existing bridge structure. In order to evaluate the scour potential of a bridge, it is necessary to have information regarding the substructure, particularly the bridge foundations. However, as of 2011 there are more than 40,000 bridges across United States with unknown foundations. Generally for these bridges there are no design or as-built plans available to show the type, depth, geometry, or materials incorporated into the foundations. Several non-destructive testing (NDT) methods have been developed to evaluate these unknown foundations. The primary objective of this research is to identify the most current and widely used NDT methods for determining the embedment depth of unknown bridge foundations and to compare these methods to an ultrasonic P-wave reflection imaging system. The ultrasonic P-wave reflection system has tremendous potential to provide more information and address several short-comings of other NDT methods. A laboratory study was initiated to explore various aspects related to the P-wave system performance, in order to characterize the limitations of the system in evaluation of unknown foundations prior to deployment in field studies. Moreover, field testing was performed using the P-wave system and a number of the current NDT methods at two selected bridge foundations to allow comparison between the results.