Research On Optical Fiber Sensing To The Structure Evolutiont Of Overlying Rock With Multi-Coal Seam Mining

For further development and utilization of coal resources and the use of multi-coal seam mining. As the increase of the cumulative mining height, the main key stratum has been influenced many times in the process of multi-coal seam mining has many influences. The movement of overlying strata of the main key stratum play a decisive role until the surface of all layers, and the damage of main key stratum affect the deformation and failure of overburdens directly in mining field.At the same time,it decided the "three zones" development height. This study from the point of main key stratum in coal mining process of deformation,and by means of theoretical analysis, numerical simulation and physical model test.Combining with these methods, the study aimed at overburdens movement evolution of the multi-coal seam in Wusu Hai in the process of mining.A systematic calculation of the position of the hard rock strata, and identify the main key position in overlying strata. Through the analysis of the lithology of roof and floor at 2# and3# coal seam, calculated the maximum height of water flowing fractured zone in the mining of 2# and 3# coal seam. The distribution characteristics of stress state and plastic zone of overlying strata are calculated by using FLAC3 D software in the process of 2# and 3# coal seam mining. The combination of FBG and PPP-BOTDA optical fiber sensing technology are applied to similar material model experiment,and the temperature compensation method is used to compensate the temperature of FBG and BOTDA for the first time in the physical model test, which solves the influence of measuring accuracy that temperature changes on the test. The method of loading by iron-sand instead of iron brick control the accuracy and continuity of loading effectively. In addition, the heating method is used to locate the optical fiber in the model, which ensures the efficiency of the optical fiber testing. Four sensing fibers and two fiber Bragg grating strain sensors were embedded in the 2 m plane stress physical model for studying the change of stress and strain of the main key stratum in the upper strata of the upper strata of the multi seam mining.The research shows that after the 2 #coal seam mining, the main key stratum is not broken, which hinders the fracture spread to the upper layer, and the upper layer of the main key stratum is in the curved sinking zone. After the 3# coal seam mining, the main key stratum is broken, and the fracture of the main key stratum causes the fracture to spread to the upper layer, and the water flowing fractured zone developed to the Luohe aquifer.The temperature compensation method should be used to compensate the FBG grating test and the BOTDA fiber test in the model test.The iron-sand loading has more accuracy relative to iron brick,and PPP-BOTDA distributed optical fiber sensing technology can monitor the movement of overburdens and the trend of development.FBG sensors can monitor the key-points of the rock movement.This experiment realizes the real-time monitoring of key-strata, which including the process of continuous changing into a semi continuous the whole and the part of, and provide the basis for the safety production of Wusu Hai.