Experimental study on overlying strata migration law of coal seam group mining based on digital speckle technology

In order to study the law of overlying strata migration and aquifer hydrodynamic evolution during mining of gently inclined and close distance coal seams, and to prevent water inrush accidents during downward mining of coal seams, the deformation and failure of roof of fully mechanized working face in No.6 mining area of a coal mine is studied by means of fluid solid coupling similar simulation test, digital speckle technology application and theoretical analysis.The results show that during the mining process of 14^# upper group coal, the isolated coal pillar can better control the movement and deformation of the roof, while the repeated mining of 15^# lower group coal will destroy the isolated coal pillar of upper group coal, resulting in the aggravation of roof deformation and failure; after the mining of coal seams, the overlying strata displacement propagation direction is vertical direction, and the displacement of the same stratum presents the characteristics of large middle subsidence and small subsidence on both sides; the maximum influence height of overburden displacement measured by digital speckle technology is 29.0 m and 32.8 m after mining 14^# upper group coal and 15^# lower group coal respectively, and compared with the calculation results of empirical formula method, the observation error is 1.8% and 5.3%; K₄ aquifer water inrush risk will occur when 14^# coal seam and 15^# coal seam are mined down successively.