Abstract:
In recent years, the pile driving analyzer (PDA) testing has become a regular part of pile quality assurance program on projects in western Canada for steel driven piles and increasingly used as it is very quick and cost effective. The PDA is normally performed on only a small selection of test piles to determine the driving criteria for the project and the possible pile capacity development within the site. The test can be performed either at end of pile driving (EOD) or beginning of restrike (BOR). Several studies have been shown that the bearing capacity of driven piles at EOD, is much less than BOR in cohesive soils since pile driving causes an increase in pore water pressure which reduce effective stresses thereby the pile capacity. As the pore water pressure dissipates, the pile start gaining capacity overtime (Pile Setup Phenomenon). Based on load and resistance factor design (LRFD) principle and the reliability theory, the Geotechnical Resistance factor (GRF) needs to be calibrated as the measured pile capacity changes overtime. The use of the higher GRFs associated with PDA tests at BOR or higher order pile capacity measuring methods can result in significant project cost savings with potentially reduce the number and length of piles.
This paper aims to develop a method to improve the recommended GRF by the Canadian Foundation Manual in respect to time of PDA tests after installation on the project for cohesive soils. Relationships are estimated using Monte Carlo Simulation method. A case study is used to demonstrate the methodology.