Low strain pile integrity testing for rock socketed bored piles in Sri Lanka

Abstract

Low strain pile integrity testing has been available over several decades. It is the widely used method of pile testing to detect serious defects in piles. The transient dynamic response (TDR) method of low strain pile integrity testing needs pile top velocity and pile top force generated by a small handheld hammer hit. The velocity and force details are useful to estimate the pile condition near the top and the stiffness of pile-soil system Researchers have proposed that dynamic stiffness at low frequencies associates to the static stiffness of pile head. The linear region of load-settlement behaviour of a pile is described by the static stiffness. However, little attention has been paid to developing a relationship between static stiffness and dynamic stiffness. The carrying capacity of pile is considered as the most important issue in pile foundations. Load Testing is the most reliable approach to evaluate the carrying capacity of piles. However, load tests are rarely performed as it is costly, labour intensive and time dependent, but all the piles are subjected to low strain integrity tests. Following the testing results, this research proposes a relationship between dynamic stiffness and static stiffness of bored piles. It is intended to evaluate the allowable carrying capacity of piles with results of low strain pile integrity testing and high strength dynamic load testing. Finally, this research presents a simple methodology to estimate the allowable carrying capacity of piles using instrumented low strain pile integrity testing. The developed methodology will be verified using field load testing results. In addition to that, the success of implementing the TDR method on bored piles is proved by case studies.