Sensors and Actuators A 167 (2011) 338–346 Contents lists available at ScienceDirect Sensors and Actuators A: Physical journal homepage: www.elsevier.com/locate/sna Monitoring of large strains in submerged geotextile tubes using plastic optical fibre sensors K.S.C. Kuang ∗ , C.Y. Tan, S.H. Chew, S.T. Quek Department of Civil and Environmental Engineering, 1 Engineering Drive 2, E1A #07-03, National University of Singapore, 117576, Singapore article info Article history: Received 1 December 2010 Received in revised form 25 February 2011 Accepted 3 March 2011 Available online 10 March 2011 Keywords: Plastic optical fibre Sensor Large strain Geotextile abstract 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. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Geosynthetics is a term referring to a class of advanced synthetic fibres used for geotechnical-related applications. Polymer-based fibres such as polypropylene, polyester, polyethylene, polyamides and polyvinylchloride represent some of the more commonly used materials for the manufacture of geosynthetics. Geosyn- thetics have been employed in a wide variety of applications including flood and scour protection, drainage and containment of dredged materials in reclamation projects, revetment structures for erosion control, soil stabilization and wall reinforcement. Available in various forms, geosynthetics are marketed as geo- textiles, geomembranes, geonets, geogrids, geocells, geofoams, geosynthetic clay liners and geocomposites. Geotextiles, one of the major classes of geosynthetic, have been used extensively in slope reinforcement and road stabilization. In land reclamation projects, disposal of large quantity of dredged soft sediments and clays requires specially designated containment areas which are bounded by containment bunds. Stacked geotextile tubes, filled with sand, offer an effective solution to form this containment bund. Wei et al. [1] reported one such case in Singapore. In this paper, the project involves the use of these geotextile tubes filled with dredged material to form part ∗ Corresponding author. Tel.: +65 6516 4683; fax: +65 6779 1635. E-mail addresses: cveksck@nus.edu.sg, ceeksck@nus.edu.sg (K.S.C. Kuang). of a revetment structure. This will serve to contain huge amount of dredged material. These tubes will be filled with the dredged material, and subsequently dumped at specific location with maximum water depth of 25 m. This project posts a challenge due to concerns over the strain development in these geotextile tubes during the filling, dumping and landing stage especially at great water depths. Continuous strain measurement of the geotextiles during these stages would provide insights into their behaviour during actual deployment. A common method in geotextile strain measurement involves the use of conventional electrical resistance-type strain gauges which are attached directly onto the geotextile substrate. In order to avoid stiffening the localized area of geotextile due to the intro- duction of the adhesive, the use of an external thin plastic strip connected to the geotextile substrate via its two plates has been reported to be successful [2]. In view of the possibility of electrical short-circuit due to water seepage into the resistance-type strain gauge, an alternative non-electrical based sensor would be desir- able. In addition, in view of the fact that the strain developed in the geotextiles could be large (up to 40%) the sensor must be capable of measuring strain level of that magnitude. Typically non-woven polypropylene geotextiles are capable of withstanding strain val- ues of 40–80%, while woven geotextiles exhibit failure strains of 15–20%. A typical high-yield strain gauge when applied directly to the geotextile can measure strains of up to 20% accurately (e.g. the YL series manufactured by Tokyo Sokki Kenkyujo Co., Ltd. (TML)). Thus, measurement of strains beyond 20% for geotextile will need an alternative sensor. 0924-4247/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.sna.2011.03.013