Basic Study On Crack And Deflection Of Rock By Optical Fiber Sensing Technology

The rapid development of optical fiber sensing technology began in 1970s with the development of the optical fiber communication technology. It is a new overlapping science. The optical fiber is a sensitive sensor itself, and can contact the quantity which will be detected and the light leading in it without any intermediate medium .In this thesis, the technology and theory of the optical fiber detection about the rock damage's beginning and developing have been studied systematically and thoroughly by means of theory research and simulated experiments with analogy material in lab. The following is the research achievement which have been gained.First of all, the macrobend and microbend losses incurred by the rock damage are analyzed by using the pattern theory of the optical fiber transmission. The bending of the fiber after it is impacted makes part of the light through it give rise to scattering loss, and then, the transmission mode coupling occurs. Besides the bend, the loss is also relative to the bending length scope (or the bending number). It can be concluded that the optical fiber assumes twist shape microbending at the place where the rock cracks by analyzing its mechanics. This has theory guidance value to the safety detection on rock engineering.Second, in this thesis the embedding technology and the interaction theory of the fiber and the base material have been studied. If the fiber is embedded into the analogy material that simulates the mining of the coal, the intelligent layer will be formed. So, the test for the fiber loss in one section becomes the explanation to the deformation, subsidence, and the expansion of the crack region in rock layer, and also becomes the description of the rupture in the rock collapse.Third, the distributed optical fiber sensing system based on bending loss is put forward to, and the snake shape sensor has been designed. The sensor can give not only microbend, but also macrobend, and so, it can satisfy the feature that the material like rock transforms from micro- to macro-deformation. The fiber OTDR technology makes it realizable of long distance detection andsingle transmission in rock engineering, and the distributed layout can make linear measure and long-term detection.Finally, by the experiment in lab and the summary to the predecessor's effort, it is pointed out that the rock's damage and development can be regarded as the course of the crack expansion that can be measured by simulated experiments. This dissertation includes results from 9 experiments at 1.2m and 2m plane stress model frames respectively to analogy the collapse of the overburden. With these experiments, the fiber's loss feature in course of collapse has been systematically analyzed, and the relation model is established between the rock deformation and the fiber loss. This provides theory foundation for the actual application of the coal and rock failure monitoring. The test system of simulated experiments has been built, and the instruments will be purchased for the purpose of science research, and then, the whole system will be formed.