Experimental Study on Different Forms of Fiber Bragg Grating Sensors Detecting for Rock Model Test

To date, the Fiber Bragg Grating sensor (FBG) is one of strain measurement elements which can be embedded inside the rock model, this providing us an effective method to detect model deformation. The attachment methods, form of FBG sensor and the coupling status between the sensor and rock model are the major obstacles in the application of FBG sensor for model test. This study tried to research the detecting behaviors of FBG sensors which were packaged in different forms and materials. Two overlying strata models were built and two different forms of FBG sensors were embedded. Two FBG sensors were embedded vertically in model 1 and 2, respectively. The dimension of two models were 500 mm (L) × 400 mm (H) × 73 mm (W). The embedded two FBG sensors were named as FBG01,02 in modell and FBG03,04 in model2. FBG01,03 used copper substrate packaging, FBG02,04 used acetate ethylene plastic cylindrical packaging. The geometric similarity ratio of modell and 2 were 1:400. The experiment results showed that the model strata settlement deformation and the wavelength shift of sensors caused by deformation have linear-relation, the correlation coefficient reached to 0.9. The average sensing ratio of acetate ethylene plastic sensor and substrate sensor were 52.22 pm/mm and 26.81 pm/mm. The average sensing ratio of acetate ethylene plastic sensor was bigger due to the physical and mechanical properties of acetate ethylene plastic were closer to the rock model. However, the substrate sensor showed a better data variance due to the surface area of substrate packaging was large than cylindrical packaging. This suggests that the FBG sensor could be better applied to the rock model test if it has a large surface area and the sensor material is closer to the rock model.