Case Studies: Use of Low Strain Transient Dynamic Response Method for Rock Socketed End Bearing Bored Piles

Abstract

The transient dynamic response (TDR) method has been introduced to pile integrity testing over several decades. The TDR method requires measuring both pile top velocity and force induced at the pile top by a small handheld hammer. Force and velocity information can be used to determine the pile condition near the top of the pile and the stiffness of pile-soil-rock system. It has been suggested by researchers that the dynamic stiffness at low frequencies obtained from the TDR method relates to the static stiffness of a pile. The static stiffness determines the initial linear region of load-displacement behavior of a particular pile. However, little attention has been paid to developing a correlation between the dynamic stiffness obtained from the TDR method and the static stiffness of a pile head. Therefore, systematic field tests were performed on rock-socketed end-bearing bored piles to determine both dynamic stiffness and static stiffness. The piles were tested using both high-strain dynamic load testing and low-strain pile integrity testing. Based on the field testing results, this paper suggests a correlation between dynamic stiffness and static stiffness. Furthermore, successful implementation of the TDR method on rock-socketed end-bearing bored piles is verified through case studies. In addition, the case studies show that dynamic stiffness and first resonant frequency could be used to identify the doubtful piles having low toe stiffness.