Study On The Expansion Law Of Sandstone Fractures Under The Action Of Carbon Dioxide Blasting

The use of explosives to increase the permeability of low-permeability sandstone type uranium deposits can effectively improve the efficiency of in situ leaching of uranium.With the increasingly strict control of explosives,shortcomings such as poor repeatability and easy collapse of holes are gradually becoming apparent,and new methods of blasting induced cracking need to be explored.In recent years,liquid CO₂phase change blasting technology has shown good blasting fracturing effects in fields such as mining and coal seam pre splitting,and has been widely applied.At present,research on phase change blasting is mainly focused on engineering applications,and it is necessary to increase research on CO₂ phase change blasting equipment,cracking mechanism,and characteristics.Based on this background,a research method combining theoretical analysis and numerical simulation is adopted to optimize the phase change cracking equipment to meet the requirements of"a large number of vent holes and uniform pressure"of the cracking device for explosive infiltration enhancement.Numerical simulation of liquid CO₂ phase change blasting based on fluid solid coupling algorithm,analyzing the crack propagation status of sandstone model after blasting.Then,according to the principle of control variates,the test scheme is designed to study the damage characteristics and crack growth law of the sandstone model under the action of control holes,repeated blasting,crustal stress and other factors.The main conclusions of this article are as follows:（1）By simulating the flow process of high-pressure CO₂ gas,the distribution characteristics of pressure reduction in the cavity of the energy release head from the right end to the left end are obtained.Combining this feature to set the pore size of the vent hole to a non-uniform type can achieve the goal of balancing the pore pressure and reducing the pressure difference.The pressure monitoring data shows that when the vent hole is symmetrically distributed,the output pressure is relatively stable.Therefore,when the vent hole is set to a non-uniform symmetric type,it can output a uniform and stable pressure,which meets the requirements of blasting permeability enhancement for the fracturing device.（2）Based on the HJC model of sandstone from a uranium mine in northern China,a compressed gas and water vapor container explosion model was used to convert the fracturing device into 249.71 g TNT for research.The results show that the crushing area generated by phase change blasting is small,and the crack length can reach 18.5times the borehole radius;compared to rectangular holes,diamond shaped porous blasting generates more cracks,stronger connectivity,and a wider range of effects.（3）The presence of control holes reflects the stress waves generated by phase change blasting,promoting the generation and development of cracks.The results show that when the distance between control holes and blast holes is set to a radius of 0.6～0.7times the crushing area,the crack network generated has the widest range of action and the best connectivity;after adding control holes to rectangular holes,the crack rate increased by 5.64%compared to before,achieving a significant improvement effect.（4）Repeated blasting mainly expands the distribution range of the blasting crushing area,but does not show an effective promoting effect on the crack expansion required for blasting infiltration enhancement.（5）During phase change blasting,crustal stress mainly limits the formation and expansion of cracks,narrows the scope of action of the crack area,and has little influence on the crushing area;as the lateral pressure ratio k increases,the cracks show a clear trend of expanding along the direction of the maximum principal stress;when the angle between the vent hole and the main stress increases,the area of the crushing zone shows an expanding trend,and its shape shows a transition from circular to rhombic to cross shaped.