Study On Crack Propagation Law Of Liquid Carbon Dioxide Phase Transition Blasting And Its Application

Liquid carbon dioxide phase transition blasting is a physical method to enhancing coal permeability.The technology is safe,convenient and of wide application.By phase transition blasting in coal,permeability is greatly improved and gas is released so that possibility of gas outburst is reduced.In addition,carbon dioxide can replace gas from coal to improve gas extraction level.By theoretical analysis,numerical simulation and field testing,study the blasting energy,crack propagation mechanism,crack propagation mechanism and blasting result systematically.The results are as follows:(1)In combination with phase characteristic of carbon dioxide,analyzed the energy change in process of phase transition blasting.According to R-K-S real gas equation,calculated expansion work of high pressure gas and blasting energy of blasting equipment.(2)In combination with blasting theory and fracture mechanics,analyzed crack propagation mechanism with liquid carbon dioxide phase transition blasting and calculated range of crushing zone and crack zone which was caused by stress wave.According to effective stress intensity factor of macro crack,analyzed crack dynamic extension mechanism.On the basis of analyzing quasi-static stress field,studied the second expansion condition of crack in middle and far area under high pressure gas.(3)On the basis of SPH calculation method,builded the gas blasting model of coal,and simulated the process of liquid carbon dioxide phase transition blasting,and studied the blasting range,damage mechanism under gas blasting.The simulation integrally showed the formation of crushing zone,the formation and extension of radial crack in the process of gas blasting.(4)According to SPH calculation method,builded the gas blasting model of coal,and studied blasting crack formation and propagation law under borehole interaction.In combination with theoretical calculation and numerical simulation,obtained the reasonable spacing of double borehole blasting.By the study of guiding mechanism of controlling hole and the simulation of double hole blasting with controlling borehole,analyzed the influence of controlling borehole on crack propagation law.Based on the analyzation of crack propagation law under different borehole layout methods,staggered plum blossom hole had uniform energy distribution and reduced energy reuse and stress concentration which induced crack to develop fully.It proved staggered plum blossom hole could produce better blasting effect.(5)By deep-hole enhancing permeability testing in the Longfeng Mine,obtained liquid carbon dioxide phase transition blasting was safe,convenient and of wide application,and works very well.Using the trace method and detection method,the blasting range of MZL-51/2000 equipment was 3m with 1.8kg liquid amount.After blasting,gas extraction concentration increased to 1.5-3 times,and achieved the goal of enhancing coal permeability.