Monitor Optics Systems, a partner of Micron Optics, recently presented two papers at the 10th Triennial Conference for Mine Subsidence, an event that took place in New South Wales, Australia earlier this month. The two papers presented by Matthew Brunton of Monitor Optics titled “Monitoring of Mining Induced Movements Between Bridge Components with Fibre Bragg Grating Sensors” and “Continuous Monitoring of Mining Induced Strain in Bridge Stepped Joints Using Fibre Bragg Grating Sensors” outline two different projects in which Fiber Bragg Gratings (FBGs) were successfully used to monitor mine subsidence.
The first paper mentioned in the above paragraph describes a novel use of Monitor Optics Systems’ (MOS) FBG sensor cables to monitor relative movements between twin bridges that form part of the M1 Motorway in Helensburgh, New South Wales. The bridges are subject to ground movements caused by subsidence from planned underground Longwall coal mining parallel to these structures. After an engineering assessment was completed, it was decided that a more accurate solution was required to measure these relative movements. The proposed solution was a system developed by MOS that consists of using their FBG sensor cables held in tension between headstocks and abutments to measure relative horizontal movements. To monitor the sensors, a Micron Optics sm125 interrogator is used. The ongoing success of the MOS FBG system has since resulted in useful information regarding the identification of trends in relative movements between bridge components and has assisted in ensuring the bridges’ safety and serviceability. For more information about this project and to read the full paper, click here.
The second paper that Matthew Brunton presented describes another use of FBG sensors where mine subsidence occurs, except this time the monitoring of strains in concrete stepped joints is discussed. A different set of twin bridges called the Douglas Park twin bridges form part of the Hume Highway (M31), spanning over the Nepean River in New South Wales. These bridges have been subject to mining-induced ground subsidence from a number of underground Longwall coal mines and it has been determined that these ground movements may overload two of the north eastern stepped joints of each bridge. These stepped joints were subsequently reinforced with carbon fibre rods, and a solution to monitor the stepped joints was required. The proposed solution from MOS was an optical fiber sensing system comprising of Micron Optics strain sensors and temperature probes to monitor strains in key concrete stepped joints of the two bridges. A Micron Optics sm125 interrogator is also used to monitor the sensors. The monitoring system has been in operation over the past nine months and continues to successfully monitor concrete strains. For more information about this project and to read the full paper, click here.
You can learn more about the use of FBGs in structural health monitoring by visiting http://www.micronoptics.com/applications/sensing-solutions/civil-structures/.