Study on mining deformation and fracture response mechanism and rock pressure law of super thick composite key roof

In order to study the movement and deformation law of the super thick composite key layer overlying the stope. Taking the geological conditions of Yima mining area as the background, a three-dimensional (3.6 m × 2.0 m × 2.0 m) three-dimensional model was built for testing, and the deformation of overlying rock was monitored in real time by using distributed optical fiber, pressure sensor and multi-point displacement meter. The results show that the changes of the frequency shift peak value of the sensing fiber in value, position and shape reflect the dynamic evolution process of the bending deformation, fracture and rotation of the key strata in the overburden. When the working face advanced to 960 m, the 40 m thick fine sandstone (sub key layer I) broke four times and was in the collapse zone; The 160 m thick conglomerate (sub key layer II) of the lower formation was broken once, but the structure was not unstable and was in the fracture zone; The 250 m thick super thick conglomerate (the main key layer) of the upper formation has slight bending deformation and is located in the bending subsidence zone. The influence of mining causes the overlying high-level giant thick conglomerate to show two deformation characteristics: the giant thick conglomerate under the sub key layer forms a number of short-distance longitudinal non-through fractures, and the giant thick conglomerate above the main key layer forms a large non-through fracture bending deformation in the horizontal layer. With the increase of mining range, the composite key layer will appear synchronous and asynchronous fracture, and the rock layer will be suspended in a large area, which is easy to induce mine dynamic disasters.