Mechanism And Experimental Study On Pre-notched Directional Fracture Caused By Carbon Dioxide

Carbon dioxide fracturing technology is a new physical "cold" blasting technology developed for high gassy mine,which is easier to adapt to the underground environment than traditional hydraulic fracturing,chemical explosive blasting,high safety,powerful,simple operation,green environmental protection and other advantages.At present,the technology of fracturing mechanism,influence scope,fracturing equivalent,crack distribution and other aspects of the theory,experiment and practice research,improve the permeability of coal seams,face outburst,roof pre splitting the upper corner of governance,weakening top coal mine safety field has been widely recognized in the high gas mine.It can be seen that the research on the technology of carbon dioxide cracking is still considered as a constant cracking method,and the research on its application is not detailed enough.In this paper,mine mining without coal pillar roof cutting into safety,fracture of roadway roof control technology of directional blasting precision,the stability of surrounding rock,using slot directional technology combined with the success in the hydraulic pressure and chemical explosive blasting technology experience,proposed carbon dioxide notched directional splitting technique,and analyzed in theory.And experimental study.First of all,the research results at home and abroad at this stage of carbon dioxide fracturing technology is summarized,the carbon dioxide fracturing hydraulic fracturing technology with chemical explosives,are briefly compared,the dynamic impact of the high-energy carbon dioxide fracturing energy mainly comes from gasification for gas and the quasi-static pressure calculation,the liquid carbon dioxide equivalent to 220 gTNT 1kg equivalent crack volume increased by 500 times,fracturing range is divided into crushing zone and fractured zone,earthquake zone,shows that carbon dioxide fracturing technology and chemical explosives in different working principle,fracture energy,fracturing effect is similar in large extent,provide a theoretical basis for the proposed cutting orientation technology for carbon dioxide.Secondly,the use of notched directional control theory,fracture mechanics theory,establishes the mechanical geometry model of notched directional splitting of carbon dioxide,carbon dioxide fracturing of V-notch,stress wave,carbon dioxide quasi-static pressure inhibition in cutting crack tip stress and cutting the root of the notch,at the same time slot tip stress intensity factor were calculated,analyzed the effect of notch crack,the propagation rule of crack.The theoretical analysis shows that the method of circular hole cutting can realize the aim of controlling the crack in the process of carbon dioxide cracking and protecting the surrounding rock.On the basis of theoretical analysis,a detailed experimental plan is established,and a carbon dioxide directional cracking experimental system is built.The theoretical study is verified by using the cement mortar model with circular holes and notched holes.The experimental results show that the slot to reduce the number of circular hole crack change distribution form,into a crack along the groove direction line,cutting the hole wall strength decreases and the stress concentration,the test block initiation pressure reduced to 50% circular hole,when the fracturing pressure is the same,because effect of cutting on energy,stress wave with obvious directivity,slot line direction of peak strain increased significantly,reduce the attenuation.The experimental research and theoretical analysis coincide,which indicates that using carbon dioxide fracturing slot cutting method can control the direction of crack propagation,and achieve the purpose of directional breaking and protecting surrounding rock.Finally,the fracturing experiment system for different cutting parameters of carbon dioxide(directional angle and depth)specimen cracking experiment,comparing the different fracturing effect,initial pressure,peak strain data,obtained the optimal parameters of the cutting angle: 60 degrees with a depth of 2/3R,and the best effect of fracturing simple process.