Pile Monitoring with Fiber Optic Sensors During Axial Compression, Pullout, and Flexure Tests

Abstract

A full-scale on-site test represents an ideal way to check a hypothesis and to determine the real behavior of structures, especially in cases in which some uncertainties cannot be reduced otherwise. To perform the test successfully it is necessary to monitor the parameters that representatively describe the structural behavior. In the case of piles, axial compression, pullout, and flexure tests cover all load combinations that may appear in service. To assess the foundation performance at a semiconductor production facility, two sets of piles with three piles in each set were tested. The monitored parameters were average strains, registered in several segments over the whole length of each pile using long-gauge fiber optic sensors. This type of sensor, combined in appropriate topologies, gives rich information concerning the piles’ behavior and soil properties. The monitoring method is presented and its performances through the results of the tests are discussed. This method allowed the determination of the Young modulus of the piles, the occurrence of cracks, the normal force distribution, and the ultimate load capacity in the case of axial compression and pullout tests, as well as the curvature distribution, horizontal displacement, deformed shape, and damage localization in the case of the flexure tests. Moreover, the pile–soil friction distributions, the quality of soil, and the pile tip force were estimated. The advantage of the presented method resides in the use of long-gauge sensors, which are insensitive to local structural defects like crack openings or air pockets and allow the collection of data on a global structural level and not on a local material level.