This paper describes the application of Fibre Bragg Grating (FBG) based sensors for monitoring road pavement strains
caused by mining induced ground subsidence as a result of underground longwall coal mining beneath a major highway
in New South Wales, Australia. After a lengthy planning period, the risks to the highway pavement were successfully
managed by the highway authority and the mining company through a technical committee. The technical committee
comprised representatives of the mining company, the highway authority and specialists in the fields of pavement
engineering, geotechnical engineering and subsidence. An important component of the management strategy is the
installation of a total of 840 strain and temperature sensors in the highway pavement using FBG arrays encapsulated in
glass-fibre composite cables. The sensors and associated demodulation equipment provide continuous strain
measurements along the pavement, enabling on-going monitoring of the effects of mining subsidence on the pavement
and timely implementation of planned mitigation and response measures to ensure the safety and serviceability of the
highway throughout the mining period.
A robust embeddable Fiber Bragg Grating based sensing cable has been developed by Monitor Optics Systems. This
sensor sees an array of Bragg Gratings encapsulated in a pultruded Glass Fiber Reinforced Polymer rod. The sensors are
easy to install and more robust than telecom standard optical fibers and can be used in a number of different applications.
An example is illustrated where the sensors have been used to instrument a section of a main highway in Australia to
measure ground strains in the road pavement as part of a pavement monitoring system. The monitoring system is being
used to monitor the effects of mining induced subsidence on the road as the main component of an early warning safety
system. The monitoring system has been continuously expanded over the last 3 years in accordance with the
advancement of the mining activity and now fields over 800 Fiber Bragg Gratings. The system proved to be reliable and
accurate and is now the primary tool for alarm triggering and response. The sensing cables are now being used to
monitor instability in embankments.
This investigation concerns the application of different techniques, including optical fibre strain sensing, pulsed Digital Speckle Pattern Interferometry (DSPI), traditional modal analysis and finite element modeling to the study of vibrating composite structures. A prototype system for condition monitoring of composite structures is being developed which relies on the on-line measurement of dynamic strains in order to detect any deterioration in performance due to the accumulation of damage. A range of carbon-fibre reinforced composite specimens that incorporate innovative Fabry-Perot interferometric long gauge-length strain sensors have been produced and tested. The optimal design of fibre sensor network configurations for the identification of different damage parameters is being aided through the development of a software simulation tool and the use of a p-version FEM package. Vibration modes of the excited structures have also been determined using an out-of-plane pulsed-DSPI system, employing a dual-cavity frequency-doubled Nd:YAG pulsed laser with a 25 Hz repetition rate. In general, experimental results compare favorably with finite element predictions. The data derived from the strain sensors is used to update a parameterized FE model of the composite structure, allowing the determination of the position and extent of damage present.
This investigation concerns the application of different techniques, including optical fibre strain sensing puIsed Digital Speckle Pattern Interferometry (DSPI), traditional modal analysis and finite element model updating procedures to the study of vibrating composite structures. A prototype system for condition monitoring of composite structures is being developed which relies on the on-line measurement of dynamic strains in order to detect any deterioration in performance due to damage. A range of carbon-fibre reinforced composite specimens that incorporate innovative Fabry-Perot interferometric long gauge-length strain sensors have been produced and tested. The optimal design of fibre sensor network configurations for the identification of different damage parameters is being aided through the development of a software simulation tool and the use of a p-version FEM package. Vibration modes of the excited structures have also been determined using an out-of-plane pulsed-DSPI system, employing a dual-cavity frequencydoubled Nd:YAG pulsed laser with a 25Hz repetition rate. In general, experimental results compare favourably with finite element predictions. The data derived from the strain sensors is used to update a parameterised FE model of the composite structure, allowing the determination of the position and extent of damage present.
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