Structure Instability Characteristics Of Hard Strata And Hydraulic Fracturing Control Technology

Roof accidents have long been ranked first in all kinds of mining accidents,from the number of accidents and death toll.According to statistics,there are about 30～40%of the coal mines in China,which are covered with one hard rock layer at least.The thickness of hard rock layers is from 6 to 10 meters and protodyakonov scale of hardness is from 4 to 5 or more.Hard rock layers structure is systematic and complex,when these mines are mined,the strata behaviors will be strong.Dynamic disasters may be induced even,such as rockburst and so on,the disasters are endangered the safety of underground workers.Therefore,study on the characteristics and control technology of hard rock layers structure instability is of great significance for safe and efficient mining.It also can realize the knowable and controllable of hard rock layers structure instability.This dissertation comprehensively applies plate and shell mechanics,plastic mechanics theory.XRD diffraction test,major element test,mechanical property test,similar material simulation test in laboratory.Geophysical test,microseismic monitoring,mine pressure monitoring in-situ tests and FLAC numerical simulation.The discriminant indicator of hard rock layers are determined by physical,mechanical and geochemical properties.The "multi-layer plate structure" system model for hard rock layers is established.It is determined that the instability process of multi-layer hard rock layers is characterized by "low layer cantilever structure→medium layer masonry structure→high layer arch pressure structure",And the hard rock layer bending equilibrium equation is established,using this equation,the calculation method of the cooperative deformation loads of the hard rock layers and the solution method of the hard rock layers deflection function are determined.Based on these methods,the characteristics of the instability scale of hard rock layers under different temporal and spatial conditions are revealed,and the influential factors of hard rock layers instability are determined.The temporal and spatial regular pattern analysis method for hard rock layers instability are formed by these results.In order to verify the theoretical analysis results,a test method for the characteristics of hard rock layers and their instability is constructed.Instability energy release characteristics of hard rock layers are revealed by using plate and shell mechanics.The instability energy release of hard rock layers is related to parameters such as length of suspension along working face,instability scale,loads,rock layer thickness,elastic modulus and Poisson’s ratio.Taking the No.8218 panel of Tashan Coal Mine as an example,the characteristics of hard rock layers instability in No.8218 panel are revealed by using the regular pattern analysis method for hard rock layers instability.And the control influence of hard rock layers instability on strata behaviors is determined in Tashan Coal Mine.According to the instability characteristics of hard rock layers,the principle of hard rock layers instability control is established,and the collaboration control technology of multi-layers hard rock is proposed.And a multi-layer hard rock groud and underground hydraulic fracturing control technology test plan is developed,based on the characteristics of hard rock layers instability No.8218 panel.On-site monitoring indicates that the structure scale of hard rock layers is controlled effectively by using these technologies,and the strength of strata behaviors in the longwall face and No.5218 gateway is reduced.The research results of dissertation provide the theoretical basis for revealing the characteristics of hard rock layers instability.The spatial position of the target hard rock layer is determined.Prediction of hard rock layers instability is realized.The multi-layer hard rock groud and underground hydraulic fracturing control technology achieves effective control of target hard rock layers,and the instability scale of hard rock layers is reduced.The research results provide theoretical guidance and technical support for similar condition coal mines.There are 118 figures,25 tables,and 147 references in the dissertation.