Distributed fiber optic sensing along driven ductile piles: Design, sensor installation and monitoring benefits

Efficient and economic foundations are essential to ensure the long-term integrity of structures. Driven ductile piles offer a safe and quick solution for foundations, which can be individually customized to changing soil conditions. Geotechnical load tests on a small subset of piles can be performed at large construction sites to examine the bearing capacity for optimization purposes. Arising deformations during these statical tests are usually measured using electrical sensors at the top, which, however, do not deliver information about the stress distribution along the pile. This paper presents a fiber optic monitoring approach, which provides distributed strain profiles with a spatial resolution of up to 10 mm along driven ductile piles. The high measurement resolution of about 1 μm/m enables the detection of local effects in the load transfer from the pile to the surrounding grout and soil. The critical sensor installation on-site as well as results of various field applications with pile lengths of up to 25 m are presented. Verification measurements at the pile’s head and internal measurements of strain gauges prove the suitability of the developed monitoring approach and demonstrate the high potential of distributed fiber optic sensing for applications in soil mechanics.