Li Jun

This paper proposes a dual-parameter strain/displacement safety monitoring technology for railway tunnel lining structures. An integrated monitoring system with FBG (Fiber Bragg grating) and VDM (video displacement meter) components was used to monitor both the strain and deformation of the tunnel cross-section. Initially, a comprehensive experimental study was carried out using FBG strain sensors with temperature-compensated grating. The temperature-compensated grating was used to further improve the monitoring accuracy. The data show that the stability and accuracy were better than the traditional electronic strain sensor. Secondly, high-precision and multipoint monitoring of railway tunnel lining deformation was achieved by using VDM technology. Three months of case study results taken from the Gansu Railway Tunnel in China demonstrated a tunnel cross-section strain accuracy for microstrain and crown deformation at the submillimeter level, respectively. The technology provides a new high-precision way to monitor the condition of tunnel lining structures.

With the rapid growth of railway mileage in China, the degree of heavy load of railway wagons continues to increase. An interference technology based on Rayleigh backscattering signal in optical fiber was proposed by using existing communication optical cables along railway lines. When the fiber vibrated slightly, the phase and refractive index of the fiber at disturbed position changed, which resulting in the Rayleigh backscattering light. By performing differential calculation on the Rayleigh signal curves before and after the operation, the location of the interference light intensity signal corresponded to the location of the disturbances was obtained. Based on this method, the recognition and positioning of railway vehicles were realized. By collecting and analyzing the time-domain and frequency-domain signal, the signal strength, train length, the number of carriages and other characteristics were extracted, and the model of railway vehicles were accurately recognized. Compared with traditional positioning technologies, this technology could realize long-distance monitoring, and the sensing fiber was buried underground on both sides of the railway, which was conducive to the concealment and protection of optical fiber. Experimental results show that the positioning error of the system is within ±10 m, and the detection of railway speed and position within 25 km can be realized.

As a micro-nano machining method, the focused ion beam (FIB) processing can be used to manufacture the nanometer elements and microstructure elements. The whole process of designing and manufacturing the 45° mirror surface at the end of multi-core fiber using focused ion beam processing technology was studied. This mirror surface was manufactured in two steps: the first was the scanning process, which was used to manufacture the rough cut surface; the second was the polishing process, which was used for the surface finish of optical surface. The machined 45˚ mirror surface could be accurately aligned with the fibre core of optical fiber, which avoided related issues of external turning mirror components docking. The experimental test show that the displacement value in two vertical axial directions can be measured by the machined structure with interferometry. The measuring range of the detection displacement is approximately 60 µm, and the absolute measurement error of root-mean-square in X and Y axial directions is 1.75‰ and 1.97‰, respectively. This technology is expected to be used in the detection fields of inner surface and vessels inter wall for precision components.