The artificial ground freezing has disadvantages such as long reinforcement time and insufficient reinforcement effect.Therefore,a novel technology of multi-refrigerant combined refrigeration is proposed.Meanwhile,a case study is conducted on a shield cutterhead replacement project in the Pearl River Delta water resources allocation,and a combined freezing scheme of liquid nitrogen+brine double-refrigerant is presented.Moreover,the feasibility of the multi-refrigerant combined freezing technology is analyzed from four aspects:geological conditions,program design,numerical calculation verification,and application effect.Some conclusions are drawn as follows:(1)The liquid nitrogen freezes quickly with poor uniformity after reinforcement,and the brine freezing freezes slowly with good uniformity,thus the combined freezing of liquid nitrogen and brine can provide conditions for shield chamber opening in high-risk strata.(2)The liquid nitrogen freezing lowers the working environment temperature of tunnel face.In this case,the temperature of the tunnel face is lower than-40℃,and the ambient temperature is approximately-13℃,thus low-temperature protection measures should be applied.(3)To ensure construction efficiency,the slurry in shield chamber should be cleaned after freezing wall intersection to prevent mud frozen.
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