The study of water-resistant key strata stability detected by optic fiber sensing in shallow-buried coal seam

The destruction of the water-resistant key strata is the root cause of water resource destruction in ecologically fragile areas and mining water hazards. Accurate and effective scientific monitoring of the stability of water-resistant key strata is an important basis for water-preserved coal mining and rock formation control. At present, drilling detection, theoretical analysis and numerical simulation are often used to calculate the height of water-conduction fractured zone to indirectly determine the aquifer permeability. With the development of optical fiber sensing technology, fiber Bragg grating (FBG) and distributed optical fiber (BOTDA) methods are used to monitor the stability of mining overburden, which provides a new research idea for water-preserved coal mining. The research show: In shallow seam, when the thickness of bedrock is only 60–67 m, the water-conduction fractured zone will develop directly to the ground surface, which will inevitably lead to the destruction of bedrock aquifer, the fracture line and its longitudinal cracks nearby prove to be the main seepage channel; the strain detected by optic fiber presents double peak characteristic due to the stress concentration of strata in fracture position, and the peak position corresponds to the fracture line. It's possible to prediction the fracture line position by optic fiber sensor; combining with the limit equilibrium theory calculation, the breaking limit strain threshold value of the water-resistant key strata based on optical fiber sensing detection is given as 2000 με. The FBG sensor can accurately monitor the deformation of rock mass at a specific location. The detection of instability position of the water-resistant key strata is basically consistent with the actual observation and distributed fiber optic detection results.