MINING-INDUCED OVERBURDEN FAILURE AND HEIGHT PREDICTION IN JURASSIC WEAKLY CEMENTED ROOF

The water-conducting fractured zone of roof after mining is an important pathway to connect the overlying aquifer. It is also a key problem to be studied in the prevention and control of roof water disaster. In recent years,the western mining area has become the main mining area of coal resources in China. Its main mining Jurassic coal-bearing strata are obviously different from the eastern Carboniferous-Permian,and have typical characteristics such as high porosity and poor cementation. The evolution characteristics of water-conducting fractures in rock roof are also quite different from those in the eastern mining area. Relevant research has not yet formed universal results. Therefore,this paper selects the typical weak cementation area-the Dananhu mining area in Hami,Xinjiang as an example. Using UDEC numerical simulation,on-site three-dimensional borehole TV imaging and other methods,combined with 'S-R'stability theory,taking the height of caving zone as an independent variable,the relationship between the bearing strength of masonry beam and the height of caving zone is established. The mining failure process and evolution characteristics of roof in the process of coal seam mining in this area are fully revealed,and the development height of roof water-conducting fractured zone is determined based on this. On this basis,by collecting the measured data of the height of the water-conducting fractured zone in the same type of the Jurassic coal mines,based on the regression analysis method,the existing empirical formula is fitted and corrected as a reference for the prediction formula of the height of the roof water-conducting fractured zone in the Jurassic weakly cemented coalfield. The results show that the development height of the roof water-conducting fractured zone in the study area is 60.07~62 m,the ratio of the height of the fractured zone to the cutting height is 17.67~18.24,and the overall shape is 'terrace' type. The reliability of the measured results is confirmed by the comparison with the field measurement of adjacent mines. The development height of the water-conducting fractured zone in the mining area is affected by the height increment of the caving zone and the change of the rock block rotation angle. The development and evolution of 'rapid increase-slow increase-gradually stable' is presented. The verification calculation results show that the prediction accuracy of the regression formula proposed in this paper is generally between 10.30% and 17.25%,which is 51.84% lower than the average error of the traditional empirical formula. The prediction accuracy of the height of water-conducting fractured zone is significantly improved. The relevant research results of the paper can provide a theoretical basis for the calculation of the development height of the water-conducting fractured zone under similar mining conditions in Xinjiang.