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Monitoring deformation and damage on rock structures with distributed fiber optical sensing
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International Journal of Rock Mechanics & Mining Sciences 41 (2004) 413
SINOROCK2004 Paper 1B 17
Monitoring deformation and damage on rock structures with distributed fiber optical sensing J. Chai*, S.M. Wei, X.T. Chang, J.X. Liu College of Energy Science and Engineering, Xi’an University of Science and Technology, Xian China
Abstract Rock deformation and damage are attributed to cracks and crack growth which must undergo a developing course of material failure from deformation to damage. This paper explains the application of fiber optical sensors for monitoring rock structures to provide an internal measurement. By studying the optical fiber bending loss due to the deformation of the lower intensity material, the authors conclude that the deformation of a rock layer and the fiber bending loss are not directly compatible if the bare optical fiber is directly embedded. So, in order to construct a microbending sensing system, it is necessary to arrange for the parameters to be measured to cause microbending of a cable which is then monitored with an OTDR system. A new test method is put forward, a type of sensor that consists of a pipe and bare optical fiber. The experiments have been performed at the Shaanxi Key Lab of Ground Control. A schematic diagram of the distributed fiber optical sensor system based on the OTDR technique in the simulation experimental model is shown in Fig. 1. In the distributed sensor system, a series of microbending deformation sensors along the sensing fiber are attached in tandem to the rock structure. The plane stress model is 1.2 m long, 0.12 m wide, and 0.45 m tall. Its geometric similarity ratio is equal to 100, unit weight ratio equals to 1.5. The snakelike fiber optical sensors (SFOS), microbending along the fiber, are attached within the two rock layers of the model. The experiment indicates that the bending loss of SFOS will be correlated with the rock deformation, damage and collapse, and the information can be acquired simultaneously. The fiber’s loss feature in the course of collapse has been systematically analyzed, and a model for the relation between the rock deformation and the fiber loss is established. Keywords: Simulation experiment; Rock deformation and damage; Distributed fiber optical sensing; OTDR; Snakelike fiber optical sensor; Bending loss
Fig. 1. Experimental test set-up for distributed fiber optical detecting system.
*Corresponding author. E-mail addresses: [email protected] (J. Chai), [email protected] (S.M. Wei). For full length paper see CD-ROM attached. doi:10.1016/j.ijrmms.2003.12.008
International Journal of Rock Mechanics & Mining Sciences 41 (2004) 413
SINOROCK2004 Paper 1B 17
Monitoring deformation and damage on rock structures with distributed fiber optical sensing J. Chai*, S.M. Wei, X.T. Chang, J.X. Liu College of Energy Science and Engineering, Xi’an University of Science and Technology, Xian China
Abstract Rock deformation and damage are attributed to cracks and crack growth which must undergo a developing course of material failure from deformation to damage. This paper explains the application of fiber optical sensors for monitoring rock structures to provide an internal measurement. By studying the optical fiber bending loss due to the deformation of the lower intensity material, the authors conclude that the deformation of a rock layer and the fiber bending loss are not directly compatible if the bare optical fiber is directly embedded. So, in order to construct a microbending sensing system, it is necessary to arrange for the parameters to be measured to cause microbending of a cable which is then monitored with an OTDR system. A new test method is put forward, a type of sensor that consists of a pipe and bare optical fiber. The experiments have been performed at the Shaanxi Key Lab of Ground Control. A schematic diagram of the distributed fiber optical sensor system based on the OTDR technique in the simulation experimental model is shown in Fig. 1. In the distributed sensor system, a series of microbending deformation sensors along the sensing fiber are attached in tandem to the rock structure. The plane stress model is 1.2 m long, 0.12 m wide, and 0.45 m tall. Its geometric similarity ratio is equal to 100, unit weight ratio equals to 1.5. The snakelike fiber optical sensors (SFOS), microbending along the fiber, are attached within the two rock layers of the model. The experiment indicates that the bending loss of SFOS will be correlated with the rock deformation, damage and collapse, and the information can be acquired simultaneously. The fiber’s loss feature in the course of collapse has been systematically analyzed, and a model for the relation between the rock deformation and the fiber loss is established. Keywords: Simulation experiment; Rock deformation and damage; Distributed fiber optical sensing; OTDR; Snakelike fiber optical sensor; Bending loss
Fig. 1. Experimental test set-up for distributed fiber optical detecting system.
*Corresponding author. E-mail addresses: [email protected] (J. Chai), [email protected] (S.M. Wei). For full length paper see CD-ROM attached. doi:10.1016/j.ijrmms.2003.12.008