Study On Deformation And Failure Mechanism Of Deep Coal Seam Floor In Xingdong Mining Area

The coal measures basement strata in Hanxing mine area is the Ordovician thick limestone,with characteristics of deep buried,karst development and better water-abundance.In recent years,with the expansion of mining depth and mining scale,the water pressure of limestone aquifer in coal floor is also increasing.The threat of high confined water in coal floor is becoming more and more serious.Especially,the risk of water inrush increases obviously after deep mining.Therefore,it is great significance to study the deformation and failure mechanism of deep coal seam floor.Taking XingDong mine as the research object,we start with the prevention and control problem of water inrush from deep coal floor.In order to solve the problems such as the difficulty in identifying deep faults in the study area and the difficulty in predicting the failure depth of coal seam floor,we studied the identification of aquifer faults and the mining effect of coal seam floor by means of theoretical analysis,simulation experiments of similar materials and numerical tests.The main conclusions are as follows:1.The theoretical analysis was used to characteristics of water inrush from deep floor and the key points of water inrush prevention.Comparison of water inrush from Ordovician aquifer after deep mining in recent years,water inrush from coal floor has the following characteristic:(1)The occurrence probability of water inrush in deep coal mining increases obviously compared with in shallow mining;(2)after the formation of water inrush channel,the evolution mode of those channels is different;(3)the water inrush range has lag feature.According to water inrush mechanism analysis and water inrush hazard evaluation,it is obtained the key points of water prevention and control in depth are the exploration and prevention of vertical water-bearing structures.2.Based on short-time Fourier transform,the fault identification method of deep Ordovician limestone was discussed.Base on the natural gamma logging while drilling data in 3d parallel directional borehole groups,it is proved that the natural gamma logging data sensitive to the fault zones in frequency domain can be obtained from parallel directional borehole in deep Ordovician 8-member pure limestone stratum.Through time-frequency analysis,the response characteristics of the natural gamma logging data to the fault zones are obtained.It is pointed out that natural gamma value in fault zones have obvious high amplitude and steep peak in frequency domain,and the amplitude of the normal fault with dip angle less than 55° are usually higher than 200 db.3.The deformation and failure laws of different levels of non-integral floor and both sides of fault were analyzed.According to the monitoring results of 3d full-field deformation strain measurement and analysis system(XTDIC),it is found that the deformation of the monitoring points at the same level of coal seam floor go through five processes,stable change stage,"waveform" appearance stage,"waveform" slowly increase stage,significant decline stage,"lag displacement" stage.The vertical displacement on both sides of two faults with different dip angles go through three processes: the stage of rapid increase of displacement,the stage of stable change of displacement and the stage of ?v-shaped? change of displacement(reverse displacement occurrence).Combined with the field test and the trend of horizontal displacement,those are pointed out that the failure of floor strata mainly occurs in "lag displacement" stage,the fracture expansion and failure in the fault zone mainly occur in the stage of ?v-shaped? change.From the Angle of cross-correlation analysis,those conclusions are obtained: the lag displacement caused by the footwall advance mode is more drastic;the influence of advancing mode on the lag displacement of coal floor is greater than that of the distance from the monitoring point to the coal floor and the buried depth.4.A numerical model for the failure of coal seam floor with "step-shaped" faults is established.According to the numerical tests,the development degree of the plastic zone of coal floor and the stability of the fault zones under the influence of different mining schemes and advance modes were simulated.Working face in the footwall should be put into the final in mining sequence and.first mining in footwall.Based on the maximum principal stress deflection angle,vertical displacement,horizontal displacement,stress,plastic zone during mining,a structural mechanical model of the stability of ladder-shaped faults‘ trapezoid waterproof coal pillars is proposed,the deformation failure mechanism of coal seam floor is summarized.5.The optimization design of water inrush prevention scheme in deep coal floor was put forward.Combined with an example of water inrush,the change of water inrush and the water inrush passage on working face were analyzed systematically.Based on the conclusions obtained above,such as the identification of deep faults,the lagging failure depth of coal floor in the mining process and the determination of mining scheme,a comprehensive water prevention and control scheme was put forward,which included exploration and treatment of water structure before mining,determination of mining scheme,monitoring during mining and treatment after mining.