Experimental study on cutting and rock breaking by liquid CO2 phase transition fracturing technology

In order to study the applicability of liquid carbon dioxide phase transition fracturing technology in cutting and rock breaking operation, the law of carbon dioxide phase transition fracturing and rock breaking under the combined action of stress wave and high-pressure carbon dioxide quasi-static load was analyzed and a pressure test platform was built. The actual measured peak discharge pressure of the carbon dioxide cracker can reach 185 MPa, and the whole process of fracturing last about 200 ms, the key parameters of fracturing were conducive to breaking the rock. Based on the engineering practice of rock tunneling, two fracturing methods have been tested. The cutting and breaking rock plan was adopted, and the blasting vibration during the test was monitored. The results showed that: compared with the method of placing a single fracturing device in each hole in Scheme 1, Scheme 2 adopted the method of multi-tubebursting with carbon dioxide fracturing equipment, combined with reasonable parameter arrangement of fracturing holes and voids, which could achieve better cutting effect. Six fracturing holes and two central empty holes are arranged in the cutting area, and each fracturing hole is equipped with two carbon dioxide breakers connected end to end. The cutting depth can reach 1.6 m in the test, and the rock breaking volume is about 4.2 m3, the cutting space can meet the excavation demand, the work efficiency is higher.Under the effect of damage accumulation, the expansion cracks at the bottom of the cave couldcreate favorable conditions for the next cycle of cutting operation.In addition,the maximum vibration velocity in the process of fracturing is 0.376 cm/s, and the vibration, noise and dust wereall small, so that the surrounding environment would not be affected.This proves that the technology is suitable for cutting and rock breaking operation, and providing new operation means and technical reference for rock roadway excavation, urban subway tunnel excavation and other projects.