Abstract: In practical engineering, the overburden deformation is difficult to be monitored by conventional testing methods. Therefore, the Brillouin frequency shift (BFS) analysis and Brillouin optical frequency domain analysis (BOFDA) technology are adopted in this research to solve the problem. Based on the coal mining processes in the field, a 4 200 mm × 250 mm × 1 600 mm (length, width and height, respectively) overlying strata model is established in the laboratory. The deformation charactistics of overlying strata during the excavation are tested through the four horizontal sensing fibers and five vertical sensing fibers embedded in the model. By comparing the experimental results with the measured displacements obtained by close range photography digital image processing technology, the relationships between the optical fiber frequency shift values, strata working face weighting and the evolution of overburden structure are revealed through the comprehensive analysis of the characteristics of mining overburden activity and the law of strata pressure appearance. Besides, the characterizing method of the development and evolution range of two zones based on optical fiber frequency shift value are also obtained. The study shows that the BOFDA technology can be used to monitor the characteristics of mining overburden activity and the law of strata pressure appearance using BFS analysis. The test results provide theoretical and experimental support for the field application of distributed optical fiber testing technology in monitoring the "two zones" deformation of overlying strata in coal mines.

Key words: distributed fiber optical sensing (DFOS), Brillouin frequency shift (BFS), model test, overlying strata deformation, two-zone monitoring