Study On Hydraulic Fracturing Law Of Thick And Hard Clamped Gangue In Full-mechanized Coal Mining With Large Mining Height

The Jurassic coatfield in the Ordos Basin is a key development area for a large-scale national coal mine group,with an idetified resource of approximately 127.9 billion tons,which is a rare prpduction base for high-quatily coal resources in the world The 2#coat seam,which is the main mining in the Jurassic coalfield,contains gangue layers of varying degrees.With the continuous deepening of deep coal development,the distribution range of the thick and hard sandstone gangue layer in the coal seam has increased significantly,and the occurrence of instability has brought serious problem to the mining of large mining height fully mechanized working faces,especially intelligent fully mechanzed mining faces.The thick sandstone inclusions that are unstable across the working face causc difficulty in cutting with high-power shearers,severe pick wear,low efficiency,and a substantial increasa in cost.In this regard,this article takes the intelligent fully-mechanized mining face in Yubei mining area as the background of the coal seam sandstone inclusion crushing project with high mining height,and adopts comprehensive methods such as theoretical analysis,physical experiment and numerical simulation to treat the thick hard sandstone intercalatef gangue layer by hydraulic fracturing.The law was studied and the gangue pre-cracking parameters were determinted;combined with the 112201 large-cutting height fully mechanizes mining face,actual on-site 210,000 square coal seam gangue pre-cracking tests were carried out.which.verified the reliability of the technical parameters of ultra-Iong hole and multi-cracked coal seams.Sex,.The main conclusions of the study are as follows:A multi-phasc coupled fracturing test system for coal and rock mass was used to design the rock mass strength degradation experimcent with pressure and time as variables for the rock mass samples in the field.The experimental resuls sihow that the increase of pore pressure makes the primary fractures in the rock mass begin to expand and increase the number of weak planes in the rock mass.Prolonging the action time can improve the water content of rock mass and the softening coefficient.Based on the theory of fracture mechanics,the crack initiation and expansion conditions of the hole wall crack are analyzed.The numerical simulation method is used to analyze the influence of different ground stress,hydraulic pressure,and crack radius on the crack initiation and propagation.The analysis shows that the fracturing scheme adopting high pressure fracturing and low pressure softening can better guarantee the effect of crushing and softening.In order to ensure that the cracks and seepage range are better controlled in the gangue layer,the cutting depth of the hole wall crack should be selected according to the thickness of the gangue layer.After the crack initiates,the direction of crack propagation is along the direction of greater ground stress;under the same conditions,the greater the stress difference,the greater the crack propagation length;within the same time step,the increase in the crack radius of the hole wall is conducive to the expansion of the crack.Through the characteristics of simultaneous expansion of multiple cracks,the influence of stress interference between cracks on the expansion of cracks is analyzed.Numerical simulation is used to analyze the evolutionary influence law of the main stress difference and different process parameters of the overall failure of long hole cracks.The analysis shows that the larger the principal stress difference is beneficial to the connection of the plastic zone between the gaps;the reasonable arrangement of the crack spacing is the key factor to ensure the overall failure of multiple cracks,followed by the crack radius and aperture.In view of the fluctuation of the occurrence of the gangue layer,a three-dimensional model of the gangue coal seam was established by using the methods of fixed-point accurate exploration,coal and rock identification and geostatistics,and a reasonable pre-fracture plan was formulated to ensure the accurate construction of the fracturing technology.Field observations verify the fracture and softening effect of hydraulic fracturing.After the implementation of pre-splitting,the production efficiency of the working face has been improved,the production energy consumption has been reduced,the operation environment of the stope has been improved,the safe and efficient transportation of the transfer equipment has been ensured,and the conditions have been created for the realization of efficient,safe and clean mining in the mine.