Optical fiber sensing and characterization of water flowing fracture development in mining overburden

With the increasing improvement of national ecological standards,the eco-environmental problems caused by shallow coal seam mining in arid and semi-arid areas of western China are becoming more and more serious.The development height detection of water conducted fracture zone is a scientific problem closely related to water-preserved coal mining,and it is an important basis for mine ecological damage monitoring and evaluation,and ecological restoration strategy.The distributed optical fiber sensing technology is applied to the similarity model test to explore the internal response relationship between the development of fracture zone and optical fiber detection data.In view of the insufficient analysis of the coupling relationship between optical fiber and mining rock mass in previous studies,the quantitative index of coupling relationship between optical fiber and mining rock mass,“optical fiber-rock mass coupling coefficient”,is put forward.The vertical zoning area of overlying strata caused by mining is divided reasonably by coupling coefficient.The study shows that there are five kinds of rock mass in contact with optical fiber:the stable strata at the top which are not affected by mining,the strata with downward movement tendency on the stable key stratum,the abscission layer empty area,the gangue area,and the coal seam floor.Based on the monitoring data,the overburden is divided into four parts:damaged area,strongly affected area,weakly affected area and unaffected area.The damaged area is the water conducted fracture zone,and the strong influence area is the strata with high internal stress concentration but complete structure,namely bending subsidence zone.The threshold value of coupling coefficient between fracture zone and bending subsidence zone is 0.65.The internal relationship between the shape of strain curve,the development height of water conducted fracture zone and the activity of key stratum is established,and the zonation characteristics of overburden are characterized by optical fiber sensing.The application of optical fiber sensing technology in monitoring the water conducted fracture zone caused by mining can promote the construction of intelligent mining and green mine.