Experimental Study on the Application of BOTDA in the Overlying Strata Deformation Monitoring Induced by Coal Mining

摘要

The coal mine working face overlying strata is often disturbed by multiple mining, leading to adverse effects on the working face's safe production and ground surface movement. In the three-dimensional physical model test with the size of 3000×2000×2000 mm, after the overburden gets stable when the first working face had been extracted, by using three vertical distributed optical fibers based on the BOTDA principle, the deformation law of the overburden caused by the contiguous coal face mining is studied. Results show that, before the working face advanced to 840 mm (near the fiber), the stress law of the overburden was as follows: the middle of the model was under pressure state and the remaining part was under tension state, and the key stratum produced stress concentration phenomena caused by the secondary mining; when the face advanced to 840 mm (through the fiber), the frequency shift curve of the key stratum and the strata on it combined, and the stress concentration in the key stratum disappeared, indicating that the bearing structure of the key stratum gets unstable; compared with the previous monitoring data, when the working face far away from the fiber, the information reflected by the frequency shift data gradually gets single when the working face is far away from the fiber compared with the previous measurement data. The overburden deformation increased dramatically after the key stratum gets unstable. The surrounding rock and fiber will detach when the stratum goes though large deformation such as abscission layer, fracture, and collapse, and the frequency shift monitored by BOTDA cannot characterize the rock deformation in this situation. The experimental method and the results of this paper serve as useful reference for the application of BOTDA technology in geotechnical engineering.