Experimental study on PPP-BOTDA distributed measurement and analysis of mining overburden key movement characteristics

Abstract

Abstract In view of underground coal mining and stratigraphic features in Qianqiu Coal Mine, a three-dimensional model of 3600 mm × 2000 mm × 2000 mm (length × width × height) is established in the laboratory. By using Brillouin Optical Time Domain Analysis (BOTDA) fiber-optic sensing technology, the distributed optical fiber monitoring method of overburden deformation is studied. And the corresponding relations between the frequency shift value of optical fiber and the deformation of overburden, and the frequency shift curve of optical fiber and the height of three zones (caving zone, fracture zone and bending subsidence zone) are analyzed. In addition, the process and mechanism of key strata breaking and separation development are discussed. The results are as follows: (1) There is a good correspondence between the deformation of overburden and the results of distributed optical fiber testing. And the optical fiber frequency shift curve reveals the deformation process of overburden in each mining stage. (2) The optical fiber frequency shift curve can be divided into three parts along the model height at the end of mining, corresponding to the height of three zones respectively. (3) At different excavation stages, the optical fiber frequency shift at a certain height of the model shows a “wave peak”, which has an obvious corresponding relationship with the position of the separation. (4) The positions of the key strata and separation are calculated theoretically, and the measured results of optical fiber are in good agreement with the theoretical values.