Study On Theory And Method Of Fiber Bragg Grating Sensing In Rock Deformation Test

Our country is one of the countries that coal mine accidents often happen. Many disasters attributed to the lack of cognizance to the mechanics action of coal and rock. So, it is more important to increase the test level and reduce the accidents. For the unique character and broad foreground of fiber Bragg grating (FBG) sensing, it is used in testing the course of rock deformation and damage. The monitor method adapt to rock is studied. This has very important practical meaning to increase our knowledge level of the mechanics action and the deformation and damage mechanism of rock.In this paper, from the undulation theory, and theoretically based on Maxwellian equation and the orthogonality relation of the FBG's transmission mode, the transmitted theory is deduced and the sensing equation is achieved. By the sensing experiment, the linearity relationship between the grating wavelength and the stain or temperature is proved, and this indicates its well testing character.The testing method of rock deformation using FBG is present, i.e. embedding and surface pasting. The embedding method includes anchor package, immediate embedding and boring with slurry. The stress character of fiber in embedding state is analyzed. The transferring equation of strain between fiber and rock is derived, and their relationship is gotten. The transferring model of fiber sticking on the surface is established, and the equation is derived considering the surface groove.When the mechanics parameters of fiber and middle medium are known, the strain transferring coefficient can be calculated, and the real strain of rock can be gotten then.It is studied of the embedding method with FBG testing the horizontal stress distribution in rock. The naked fiber is embedded in the simulation model, and the wavelength drift during mining is monitored. With the result of strain transferring analysis, the horizontal stress near gratings can be gained by the drifts, and the distribution can be achieved by FBG multi-point test. The result indicates that the stress can be tested by FBG, and this can be proved by numerical simulation.The test of rock uniaxial compression in MTS by the surface pasting of FBG is firstly conducted in our country in this paper. To monitor the strain change of the sample under compression, two gratings are stuck on the surface respectively along axial and radial direction. To compare the result, the electrical strain gauges are pasted on the same position. The result indicates that the testing effection of FBG is obviously better than the electrical strain gauges and the radial strain gauge of MTS, and coincident with MTS'axial displacement gauge. The experiment illuminates the good test capability of FBG, and validates the established transferring model of surface pasting.The monitoring to the subsidence of unconsolidated soil layers around the shaft in Jisan Coal Mine with FBG embedding is applied, and the boring method is used. The transferring relationship between the sensors and soil layers is analyzed, and the corresponding coefficient of wavelength and strain is derived. By 8 monthes monitoring, many observation data are gained, and the layer with the biggest subsidence is known form the analysis to the data.This provides the necessary guidance for damage forecast and maintenance timely of the shaft.