Freezing pipe structure capable of forming variable freezing zones and its artificial ground freezing method

Liquid nitrogen freezing pipe with thermal insulation members and temperature-linked discharge valves for controlling freezing range

This technology features a variable freezing pipe structure and artificial ground freezing method. It circulates refrigerant through the inner pipe of a double-walled underground freezing pipe to exchange heat with the ground via the outer pipe, while using thermal insulation attachments and members placed at intervals on the outer pipe to direct the growth of the frozen body only in desired directions.

While artificial ground freezing is highly safe for creating frozen walls in soft ground or water-bearing sand layers, it is costly to construct and maintain, and is heavily influenced by surrounding terrain. Existing technologies that use protruding members on the outer pipe to increase refrigerant residence time often lead to over-freezing in areas intended for excavation, reducing efficiency and wasting refrigerant on unnecessary areas.

This technology uses a refrigerant tank and supply pump to feed the inner pipe. It measures the temperature of the refrigerant in the outer pipe; if it falls below a set point, the discharge valve closes to retain the refrigerant, and if it rises, the valve opens to vent it. A freezing measurement unit digitizes the temperature and thickness of the frozen body, allowing a maintenance valve to regulate injection volume. The system uses austenitic stainless steel pipes and liquid nitrogen. It is suitable for urban subway tunnel and shaft excavation, water-bearing soft ground utility tunnels, and emergency excavation, preventing over-freezing to maintain equipment efficiency and reducing liquid nitrogen consumption by selectively venting only spent refrigerant.

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Key Features:

• A freezing pipe comprising an inner pipe for refrigerant injection, an outer pipe spaced apart from the inner pipe for heat exchange with the ground, and a discharge unit for venting refrigerant to the atmosphere
• A freezing range control unit comprising multiple thermal insulation attachments installed at predetermined intervals on the outer circumference of the outer pipe, and thermal insulation members in the spaces between them
• A refrigerant supply unit comprising a refrigerant tank, a supply pump for feeding the inner pipe, and a temperature sensor for measuring the refrigerant in the outer pipe
• A refrigerant discharge control unit that closes the discharge valve to retain refrigerant when the measured temperature is below the set point, and opens it to vent to the atmosphere when higher

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This invention was developed with support from the Korea Agency for Infrastructure Technology Advancement (KAIA) for the development of risk management technology during design and construction phases.

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