Abstract Nondestructive pile integrity testing (PIT) methods based on the propagation of sonic/ultrasonic waves have been widely used for the quality assurance of newly constructed drilled shafts. However, application of these techniques for forensic investigations of existing piles may encounter difficulties that are due to the existence of a pile cap. In this article, the boundary effects of pile caps on the signal of PIT methods were studied by numerical simulation and tests on three model piles. The feasibility of assessing the integrity of a capped pile by embedded accelerometers was also investigated. Results of this study indicate that it is too difficult to assess the integrity of a capped pile with the conversional Sonic Echo PIT method. On the other hand, it is possible to detect the defect or pile toe with embedded accelerometers, especially when multiple receivers are used with the Ultra Seismic techniques.