Research On Crack Propagation Regularity Of Rock Fracture Caused By Liquid Carbon Dioxide Phase Change

Since many excavation projects are located in urban areas,scenic areas,etc.,and have high requirements for vibration and environmental protection restrictions,in order to reduce the impact on the surrounding environment,it is not appropriate to use traditional excavation methods.As a physical excavation method,carbon dioxide phase transition-induced fracture rock is simple and convenient to operate,environmentally friendly and economical,and can overcome the disadvantages of traditional chemical explosion.However,there are few theoretical studies on rock fracture caused by liquid carbon dioxide.Therefore,it is of great significance for engineering applications to study the propagation law of rock-breaking cracks under the impact of liquid carbon dioxide phase change.In this paper,a self-built experiment system for liquid carbon dioxide phase change shock is used.The single-hole cracking experiment under different confining pressure constraints and the double-hole cracking experiment under the combination of different airflow directions are designed.During the experiment,the impact load was experimented and recorded.And the energy generated by the high-pressure airflow impact caused by the phase transition of liquid carbon dioxide was calculated and analyzed in combination with theoretical knowledge,which provided data support for the numerical simulation.The experimental results were combined and analyzed,and the following major outcomes:(1)In the single-hole cracking experiment,the crack expands in the radial direction with the reserved hole as the center.Under the constraint of two-way confining pressure,the confining pressure in the Y direction is kept at 5MPa,and the confining pressure in the X direction is changed.The cracks inside the concrete under the impact of the high-pressure airflow generated by the phase transition tend to the Y direction of the maximum confining pressure.When the confining pressure constraint in the X direction is gradually increased,the decreased crack growth in the Y direction is reflected from the measured damage values.(2)In the double-hole cracking experiment,under the condition of different combined action schemes of airflow impact direction,when the release port is set to face opposite impacts in the X direction,the superposition of the stress waves does not affect its continuous expansion and penetration towards the initial expansion direction.When the release port is set for the relative impact in the X direction,under the influence of the superposition of stress waves,a through crack cannot be formed between the two holes.When the direction of the release port is set to be impacted in the same direction in the Y direction,under the influence of the superposition of the stress waves,the cracks generated by the initial impact continue to expand downward,and at the same time,multiple cracks will expand to the surrounding area.(3)LS-DYNA is used for numerical simulation,and by simulating single-hole and double-hole cracking,the stress cloud map and damage cloud map at different times during the cracking process can be further analyzed.The single-hole fracture only changes the confining pressure applied in the X direction.It can be clearly found that the area of the damage zone generated in the Y direction decreases with the increase of the confining pressure applied in the X direction,and the damage zone area generated in the X direction does not change significantly.In the case of double-hole cracking,the crack of the specimen with relative impact in the X-direction can eventually form a through-crack between the two holes through expansion,and the crack in the initial direction also expands through the left and right sides.The cracks of the specimen under the opposite impact in the X direction mainly expand to the surrounding of the reserved hole,forming multiple cracks.Under the same impact in the Y direction,the tensile failure continues to expand outward in the opposite direction of the initial airflow impact direction.The crack growth between the two holes is stronger than that of the sample under the opposite impact in the X direction,but no through cracks are formed.The simulation results are in good agreement with the fracture distribution obtained from the experiment.This paper has a total of 59 figures,11 tables,and 80 references.