Short-Term Setup of Jacked Piles in a Calibration Chamber

Abstract

The time-dependent increase in axial resistance (setup) of jacked or driven piles in sand is still not well understood, and its quantification remains a challenge. In this paper, a series of tests is performed on model piles jacked in sand in a half-cylindrical calibration chamber with image analysis capabilities to study setup. Load cell measurements, which are used to determine changes in pile resistance with time, are considered in combination with digital images taken with CMOS cameras and a handheld microscope positioned in front of the transparent observation windows of the chamber. Using the digital image correlation (DIC) technique, images taken during pile installation and throughout a waiting period of up to 1 days are analyzed to detect any change in the displacement and strain field in the sand domain that would indicate stress redistribution leading to changes in axial resistance. In addition, images of a set of 5 particles are analyzed to investigate any possible enhancement of particle interlocking or any other change in particle position or orientation during the waiting periods. The results of the analyses show negligible relative displacements and strains in the sand domain and negligible displacement or rotation of individual sand particles. These results are consistent with the measured axial capacities of the model piles, which are largely the same regardless of the time after installation at which the load tests were performed.