When should I use ground freezing in trenchless construction?

Q:

When should I use ground freezing in trenchless construction?

A:

Ground freezing, also known as artificial ground freezing, is a temporary soil stabilization technique typically used in the trenchless construction of underground shafts, mines and tunnels. It essentially involves using a network of pipes to circulate refrigerant in the vicinity of the bore location to freeze the surrounding soil. The frozen soil, which can be as hard as concrete, is highly stable and allows trenchless tunneling to be performed in challenging ground conditions.

Ground freezing is typically used in situations where conventional temporary stabilization methods, such as dewatering, shoring, grouting, or soil mixing are not possible or feasible. This can occur in excavations where groundwater pressures are excessive or where the surrounding soil is highly unstable.

Artificial ground freezing creates a block of ice around the area under consideration, which is then penetrated by the tunnel boring machine (TBM) to form an opening lined with a solid, high-strength wall of ice. This method stabilizes the surrounding area before tunneling commences, making it ideal for boring in extremely weak soils that require immediate stabilization. Since the soil is stabilized in advance, ground freezing can be used to bore tunnels close to adjacent existing infrastructure with minimized potential for soil disturbance and ground settlement.

This technique should also be considered in tunneling applications where a considerable amount of groundwater is present. Freezing the soil before the commencement of boring operations allows tunneling to be performed without the risk of groundwater intrusion. Not only is nearby groundwater frozen and solidified in advance, but the ice wall also acts as a barrier which prevents water from entering the excavated area.

This method is especially valuable where the quantity of groundwater near the excavation exceeds reasonable pumping capacities.

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Written by Krystal Nanan
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Krystal is a civil engineer and project manager with an MSc in Construction Engineering and Management. Her experience includes the project management of major infrastructure projects, construction supervision, and the design of various infrastructure elements including roadway, pavement, traffic safety elements and drainage.

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