Distribution Characteristics Of Gas-phase Shock Energy Deriving From Liquid CO₂ Phase Transition In The Borehole

Liquid CO₂ gas-phase shock belongs to pure physical blasting,which has the advantages of safety and environmental protection,strong adaptability,simple operation and low cost.The energy jetting from liquid CO₂ cartridge is the unique power to fracture coal and rock mass.Researching on the distribution characteristics of gas-phase shock energy in the borehole is of great significance in the study of rock cracking and its mechanism.In this paper,laboratory tests,theoretical analysis and numerical simulation are carried out according to the distribution characteristics of liquid CO₂ cartridge gas-phase shock energy in the borehole.The researches on the distribution characteristics of gas-phase shock energy with consider-ing axial and radial seepage show that:shock waves are generated at the initial stage of the gas-phase shock,which interact with the reflected stretch wave on the wall and the high-speed and high-pressure supercritical CO₂ fluid.As a result,the maximum detonation energy of the borehole is significantly concentrated in the jet core impact area of the gas-phase shock.And the peak detonation energy decreases approximately in the form of exponential function nonlinearity with the increasing distance from the forward core impact area of the gas-phase shock.Moreover,the larger the angle of deviation from the core impact zone along the ring of borehole,the smaller the peak impact pressure of the hole wall.The time history curves of gas-phase shock energy show a typical triangular pulse characteristic of rapid linear rise before peak and exponential or power function nonlinear decrease after peak.Even the maximum peak pressure can reach 209.55 MPa,and the pre-peak boost holding time is about 1²0 ms.The post-depressurization holding time above 5 Mpa is about 600⁸00 ms,which is much higher than the pre-peak booster time.The main energy of gas-phase shock energy is concentrated on the frequency band of 0¹50 Hz.Compared to conventional chemical explosion,the gas-phase shock load belongs to the medium frequency dynamic load with a long duration.The post-peak boost holding time is much larger than the pre-peak boost time.In the early and middle stage of gas-phase shock,the boreholes are acted on by strong dynamic load and quasi-static state respectively.Most of the blasting energy accumulates around the seepage hole and eventually seeps out through the seepage hole.Based on the SW equation of CO₂,the theoretical model of permissible coal mine explosive equivalence of gas-phase shock energy under isentropic and isothermal conditions was established.Theoretical analysis show that the equivalence of coal mine ammonium ladder explosive increases with the increase of the pressure in the chamber of the liquid CO₂ cartridge.Under the isentropic condition,it increases linearly;under the isothermal condition,it increases linearly.But at the same initial state,the equivalence of coal mine ammonium ladder explosive based on isothermal calculation is higher than that based on isentropic calculation.Based on the compressible real gas hydrodynamics,the theoretical model of one-dimensional liquid CO₂gas-phase shock was established.The effects of chamber pressure,temperature and chamber outlet pressure on the impact pressure of gas-phase shock jet are analyzed quantitatively;Combined with the numerical simulation results,the one-dimensional gas-phase shock jet theory is extended to the calculation of wall impact pressure in the two-dimensional case of T-type structure.The research results obtained in this paper on distribution characteristics of gas-phase shock energy deriving from liquid CO₂ phase transition in the borehole are of great significance to the improvement of the theoretical basis of gas-phase shock.This paper includes 35 figures,9 tables and 142 references.