Monitoring of large strains in submerged geotextile tubes using plastic optical fibre sensors

The measurement of large strains in geotextile sheets in the order of a few tens of percentage strain (up to 40% in this study) has been achieved using plastic optical fibre (POF) sensors. These instrumented geotextile sheets were manufactured in a form of geotextile tubes which were strategically dumped from a barge into water depth of up to 25 m. In the sensor evaluation phase, POF sensors were mounted onto geotextile sheets and tested using a tensile testing machine with customized wide-width grips and the results compared to a reference video-capture strain measurement system. Model instrumented geotextile tubes were also built and tested in a geotechnical centrifuge at 100 × g to simulate the on-site dumping condition. The entire POF sensor system was also evaluated in terms of its waterproofing resistance by submerging a POF-instrumented geotextile sheet underwater. The instrumented geotextile mat was also subjected to water pressure equivalent to 25 m water depth in the field to assess the survivability of the system under on-site condition. Finally, results based on recent field work where the POF sensors were attached to full-size submerged geotextile tubes will be highlighted.