Measurement of pile load transfer using the Fiber Bragg Grating sensor system

Abstract

A series of laboratory and field tests were performed to evaluate the applicability of an optical fiber sensor system in the instrumentation of piles. A multiplexed sensor system, constructed by arranging several Fiber Bragg Grating (FBG) sensors along a single line of optical fiber, is capable of measuring local axial strains as a function of wavelength shifts. The distributions of axial load in three model piles and a field test pile evaluated from the strains measured by FBG sensors are found to be comparable, in terms of both magnitude and trend, with those obtained from conventional strain gauges. This suggests that the FBG sensor system is an effective tool for the analysis of the axial load transfer in piles. The successful instrumentation of a soil–cement injected precast (SIP) pile using FBG sensors suggests that the use of these sensors in drilled shafts and other types of cast in situ concrete piles is feasible. With the rapid advance of optical fiber sensor technology, the economics of the use of optical fiber sensors in this type of instrumentation is expected to improve significantly in coming years.Key words: pile foundation, load transfer, fiber optic sensor, Fiber Bragg Grating sensor.