Understanding the real performance of geotechnical structures using an innovative fibre optic distributed strain measurement technology

Field monitoring is essential in geotechnical engineering in order to ensure that (i) the design is sound, (ii) the construction is executed safely, and (iii) the geotechnical structure we built satisfies the specifications set by the clients. It has to be part of gaining engineering experience by comparing the actual behaviour with the design prediction. In this paper, an innovative distributed fibre optic strain measurement system is introduced. The system allows us to have thousands of "strain gauges" along a single cable connected to structures, embedded in soil or grouted into boreholes. Because of the simple and quick installation technique, distributed optical fibre sensing can be as equally practical as the other conventional measurements. This paper describes several case studies where fibre optic based distributed strain measurement systems were used to monitor the performance of geotechnical structures during construction or when influenced by adjacent structures. The distributed nature of strain data provided additional insights into the "real" behaviour of piles, retaining walls and tunnels, which would be difficult to gain from conventional monitoring systems. The understanding of the actual or 'real' performance of geotechnical structures provides more opportunity for us to make potentially more economical (i.e. smaller diameter pile, thinner wall or less reinforcement) and yet safe geotechnical structures. By using recent advances in field instrumentation and monitoring systems, we can be more proactive than we used to in closing the gap between theory and applications.