Experimental study and engineering application of coupling performance between distributed embedded optical fiber and tunnel lining

The coupling performance of embedded optical fiber and tunnel lining is studied using theoretical and experimental methods, and then is verified in practical engineering. We calculate the strain transmission efficiency of fiber by modeling and analyzing the structure of optical fiber, intermediate and matrix. Totally two sets of experiments are designed. The reinforced concrete beams with 6 kinds of optical fiber layout are designed in same working condition. The multistage loading was carried out at a single point in the way of displacement control. At the same time, 6 optical fibers are monitored based on the BOFDA (Brillouin optical frequency domain analysis) technology. The results of two different groups show the similar law: six optical fibers can effectively monitor the process of beam loading from the stage of beginning to the stage of yielding, and the coupling between fiber and beam is good in this process. When the reinforcement begins to yield to the failure process, the fiber strain no longer increases, even decreases or presents the state of fiber fracture, and the coupling of the fiber and the beam is poor in this process. Except for the slotted embedded fiber, the effective monitoring strain difference is 3 000x10(-6), the effective strain difference of the remaining fiber is 2 000x10(-6). Under the condition of long distance (>> 146 mm) embedding, the strain transmission efficiency of optical fiber is close to 100%. Taking the underground excavation section of the new built airport in Beijing as an example, the fiber is embedded in the two waist and vault of the initial lining, and the construction process of the CRD method is monitored by monitoring fiber. Monitoring results show that the embedding technology is feasible, which is able to provide references and valued suggestions for other related monitoring projects.