Ground freezing

Ground freezing is a construction technique used in circumstances where soil needs to be stabilized so it will not collapse next to excavations, or to prevent contaminants spilled into soil from being leached away.[1] Ground freezing has been used for at least one hundred years.

Pipes are run through the soil to be frozen, and then refrigerants are run through the pipes, freezing the soil.[1] Frozen soil can be as hard as concrete.

Soil contaminated with radioactive elements that leaked from Japan's Fukushima Daiichi nuclear power plant was contained through ground freezing.[1]

A project in Boston known as the Big Dig used ground freezing during some of its tunneling, to allow its wide tunnels to be built under or through soil that supported existing infrastructure that would have been difficult or expensive to support using more traditional excavation methods.[1]

Some ground freezing projects use common salt brine as the refrigerant,[2] but other projects benefit from using more exotic refrigerants, like liquid nitrogen.[1][3]

In Northern Canada and Arctic Alaska, passive pipe systems are used that do not require any external power to keep the ground frozen.[4] These systems use in-ground evaporators and above-ground radiators filled with liquid refrigerant. When ambient temperatures fall below ground temperatures, the liquid vapor starts condensing in the radiator, reducing the pressure in the system causing the liquid in the evaporator to boil and evaporate. This process results in heat transfer from the ground to the air and keeps the ground in a permanent frozen state.[5]

Ground Freezing System in Operation while Commuter Trains Run Through the Big Dig
Ground freezing allowed tunnels to be excavated under an active railyard during Boston's Big Dig. Each white lump marks the top of a deep ground-freezing tap.
Cross section of a ground freezing pipe as used in the big dig
Cross section of a ground freezing pipe as used in the Big Dig.

See also

  • Pykrete, a composite building material which utilizes similar properties in frozen sawdust


  1. ^ a b c d e Jessica Morrison (2013-10-30). "How Engineers Use Ground Freezing to Build Bigger, Safer, and Deeper". PBS. Archived from the original on 2014-04-11. Retrieved 2014-07-22. The basic premise behind ground freezing is that soil—made up of bits of minerals and organic matter, water, and air—becomes stronger and less penetrable when its water freezes and expands.
  2. ^ "Technical Manual for Design and Construction of Road Tunnels - Civil Elements". US Department of Transport. Archived from the original on 2013-12-05. Retrieved 2014-07-22. In order to maintain support to the tunnel face, excavation and jacking normally carried out alternately in small increments, typically in the range of 2 to 4 feet. In most cases, the soft ground must be treated by means of ground improvement techniques such as ground freezing, jet grouting, etc. as discussed in Chapter 7 Soft Ground Tunneling to enhance its stand up time.
  3. ^ "Ground Freezing: Freezing soil with liquid nitrogen". The Linde Group. 2014. Archived from the original on 2014-02-26. Retrieved 2014-07-22. During the last two decades soil freezing with liquid nitrogen (LIN) has developed from an exotic gas application with lots of uncertainties into a standard procedure for treating unstable soil and leakages.
  4. ^ Igor Holubec, Ph.D., P.Eng (2014). "Flat Loop Thermosyphon Foundations in Warm Permafrost" (PDF). Government of the NT Asset Management Division Public Works and Services. Archived (PDF) from the original on 2015-04-02. Retrieved 2015-06-12. Passive cooling by means of pressured heat exchange pipes was developed in Alaska by the U.S. Army Corps of Engineers in 1965 to preserve foundations in ‘warm’ permafrost.
  5. ^ "Thermosyphon Technology for Ground Freezing". 2014. Archived from the original on 2014-11-26. Retrieved 2015-06-12. The basis of thermosyphon thechnology is a heat transfer device (thermosyphon) which extracts the heat from the soil during winter and passes it to the environment.

A borehole is a narrow shaft bored in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extraction of water, other liquids (such as petroleum) or gases (such as natural gas), as part of a geotechnical investigation, environmental site assessment, mineral exploration, temperature measurement, as a pilot hole for installing piers or underground utilities, for geothermal installations, or for underground storage of unwanted substances, e.g. in carbon capture and storage.


Clay is a finely-grained natural rock or soil material that combines one or more clay minerals with possible traces of quartz (SiO2), metal oxides (Al2O3 , MgO etc.) and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure. Clays are plastic due to particle size and geometry as well as water content, and become hard, brittle and non–plastic upon drying or firing. Depending on the soil's content in which it is found, clay can appear in various colours from white to dull grey or brown to deep orange-red.

Although many naturally occurring deposits include both silts and clay, clays are distinguished from other fine-grained soils by differences in size and mineralogy. Silts, which are fine-grained soils that do not include clay minerals, tend to have larger particle sizes than clays. There is, however, some overlap in particle size and other physical properties. The distinction between silt and clay varies by discipline. Geologists and soil scientists usually consider the separation to occur at a particle size of 2 µm (clays being finer than silts), sedimentologists often use 4–5 μm, and colloid chemists use 1 μm. Geotechnical engineers distinguish between silts and clays based on the plasticity properties of the soil, as measured by the soils' Atterberg limits. ISO 14688 grades clay particles as being smaller than 2 μm and silt particles as being larger.

Mixtures of sand, silt and less than 40% clay are called loam. Loam makes good soil and is used as a building material.

Exploration geophysics

Exploration geophysics is an applied branch of geophysics, which uses physical methods, such as seismic, gravitational, magnetic, electrical and electromagnetic at the surface of the Earth to measure the physical properties of the subsurface, along with the anomalies in those properties. It is most often used to detect or infer the presence and position of economically useful geological deposits, such as ore minerals; fossil fuels and other hydrocarbons; geothermal reservoirs; and groundwater reservoirs.

Exploration geophysics can be used to directly detect the target style of mineralization, via measuring its physical properties directly. For example, one may measure the density contrasts between the dense iron ore and the lighter silicate host rock, or one may measure the electrical conductivity contrast between conductive sulfide minerals and the resistive silicate host rock.

Frost heaving

Frost heaving (or a frost heave) is an upwards swelling of soil during freezing conditions caused by an increasing presence of ice as it grows towards the surface, upwards from the depth in the soil where freezing temperatures have penetrated into the soil (the freezing front or freezing boundary). Ice growth requires a water supply that delivers water to the freezing front via capillary action in certain soils. The weight of overlying soil restrains vertical growth of the ice and can promote the formation of lens-shaped areas of ice within the soil. Yet the force of one or more growing ice lenses is sufficient to lift a layer of soil, as much as 1 foot (0.30 metres) or more. The soil through which water passes to feed the formation of ice lenses must be sufficiently porous to allow capillary action, yet not so porous as to break capillary continuity. Such soil is referred to as "frost susceptible". The growth of ice lenses continually consumes the rising water at the freezing front. Differential frost heaving can crack road surfaces—contributing to springtime pothole formation—and damage building foundations. Frost heaves may occur in mechanically refrigerated cold-storage buildings and ice rinks.

Needle ice is essentially frost heaving that occurs at the beginning of the freezing season, before the freezing front has penetrated very far into the soil and there is no soil overburden to lift as a frost heave.

Frost line

The frost line—also known as frost depth or freezing depth—is most commonly the depth to which the groundwater in soil is expected to freeze. The frost depth depends on the climatic conditions of an area, the heat transfer properties of the soil and adjacent materials, and on nearby heat sources. For example, snow cover and asphalt insulate the ground and homes can heat the ground (see also heat island). The line varies by latitude, it is deeper closer to the poles. Per Federal Highway Administration Publication Number FHWA-HRT-08-057, the maximum frost depth observed in the contiguous United States ranges from zero to about eight feet (2.4m). Below that depth, the temperature varies, but is always above 0 °C (32 °F).

Alternatively, in Arctic and Antarctic locations the freezing depth is so deep that it becomes year-round permafrost, and the term "thaw depth" is used instead. Finally, in tropical regions, frost line may refer to the vertical geographic elevation below which frost does not occur.Frost front refers to the varying position of the frost line during seasonal periods of freezing and thawing.

Gas hydrate pingo

A gas hydrate pingo (GHP) is a submarine dome structure formed by the accumulation gas hydrates under the seafloor. Gas hydrate pingos resemble the pingo landforms found on land in periglacial regions.Gas hydrate pingo may accumulate non-hydrate gas under pressure leading to explosions that forms craters. Crater depressions of this type have been found on the seafloor of Barents Sea. The trigger for the explosions may be drop in pressure as result of lowering of the sea level.A study in the Norwegian Sea found that gas hydrate pingoes were covered by bacterial mats and that Polychaete tubeworms that are associated with methane.


Gravel is a loose aggregation of rock fragments. Gravel is classified by particle size range and includes size classes from granule- to boulder-sized fragments. In the Udden-Wentworth scale gravel is categorized into granular gravel (2 to 4 mm or 0.079 to 0.157 in) and pebble gravel (4 to 64 mm or 0.2 to 2.5 in). ISO 14688 grades gravels as fine, medium, and coarse with ranges 2 mm to 6.3 mm to 20 mm to 63 mm. One cubic metre of gravel typically weighs about 1,800 kg (or a cubic yard weighs about 3,000 pounds).

Gravel is an important commercial product, with a number of applications. Many roadways are surfaced with gravel, especially in rural areas where there is little traffic. Globally, far more roads are surfaced with gravel than with concrete or tarmac; Russia alone has over 400,000 km (250,000 mi) of gravel roads. Both sand and small gravel are also important for the manufacture of concrete.

Ice storage air conditioning

Ice storage air conditioning is the process of using ice for thermal energy storage. This is practical because of water's large heat of fusion: one metric ton of water (one cubic metre) can store 334 megajoules (MJ) (317,000 BTU) of energy, equivalent to 93 kWh (26.4 ton-hours).

Ice was originally obtained from mountains or cut from frozen lakes and transported to cities for use as a coolant. The original definition of a "ton of cooling capacity" (heat flow) was the heat needed to melt one ton of ice in a 24-hour period. This heat flow is what one would expect in a 3,000-square-foot (280 m2) house in Boston in the summer. This definition has since been replaced by less archaic units: one ton HVAC capacity is equal to 12,000 BTU per hour. A small storage facility can hold enough ice to cool a large building from one day to one week, whether that ice is produced by anhydrous ammonia chillers or hauled in by horse-drawn carts.

Ground freezing can also be utilized; this may be done in ice form where the ground is saturated. Systems will also work with pure rock. Wherever ice forms, the ice formation's heat of fusion is not used, as the ice remains solid throughout the process. The method based on ground freezing is widely used for mining and tunneling to solidify unstable ground during excavations. The ground is frozen using bore holes with concentric pipes that carry brine from a chiller at the surface. Cold is extracted in a similar way using brine and used in the same way as for conventional ice storage, normally with a brine-to-liquid heat exchanger, to bring the working temperatures up to usable levels at higher volumes. The frozen ground can stay cold for months or longer, allowing cold storage for extended periods at negligible structure cost.Replacing existing air conditioning systems with ice storage offers a cost-effective energy storage method, enabling surplus wind energy and other such intermittent energy sources to be stored for use in chilling at a later time, possibly months later.


Lithalsa is a frost-induced raised land form in permafrost areas with mineral-rich soils, where a perennial ice lens has developed within the soil. The term sometimes also refers to palsas and pingos.

Marina Bay MRT station

Marina Bay MRT station (NS27/CE2/TE20) is an underground Mass Rapid Transit (MRT) interchange station on the North South Line and Circle Line, located on the boundary of Downtown Core and Straits View planning areas, Singapore.

It was the southern terminus on the North South Line until 2014 when Marina South Pier MRT station opened although there are frequent train services terminating at this station, possibly owing to the low ridership of Marina South Pier station. Currently, Marina Bay station is the terminus of the Circle Line Extension.

The Circle Line section of the station was awarded the winner of the Small Project Award at the World Architecture Festival in 2012.When Stage 3 of the Thomson-East Coast Line opens in 2021, Marina Bay station will become a triple-line interchange, joining Dhoby Ghaut MRT station and Outram Park MRT station. Ground freezing will be applied for the first time in Singapore rail construction when building the Thomson-East Coast Line part of this station, where it under-crosses the existing North South Line and Circle Line tunnels.Even though this station was named after the Marina Bay, it is not the nearest MRT station to the bay; Bayfront MRT station and Downtown MRT station are all nearer to Marina Bay than Marina Bay station is.

In 2025, when Stage 6 of the Circle Line opens, Marina Bay station will be directly linked to HarbourFront MRT station via Singapore's southern coast, thereby "closing the circle".

Museumsinsel (Berlin U-Bahn)

Museumsinsel is a subway station under construction in Berlin's Mitte district. It is part of the extension of the subway line from Alexanderplatz to Brandenburger Tor, with ground broken in 2010. Both should be opened simultaneously in 2020.


A pingo, also called a hydrolaccolith or a bulgunniakh, is a mound of earth-covered ice found in the Arctic and subarctic that can reach up to 70 metres (230 ft) in height and up to 600 m (2,000 ft) in diameter. The term originated as the Inuvialuktun word for a small hill. The plural form is "pingos". The term is also used for depressions, often water filled, formed by the melting of ice at the end of the last glaciation.A pingo is a periglacial landform, which is defined as a nonglacial landform or process linked to colder climates.

"Periglacial" suggests an environment located on the margin of past glaciers. However, freeze and thaw cycles influence landscapes outside areas of past glaciation. Therefore, periglacial environments are anywhere that freezing and thawing modify the landscape in a significant manner. They are essentially formed by ground ice which develops during the winter months as temperatures fall.


Sand is a granular material composed of finely divided rock and mineral particles. It is defined by size, being finer than gravel and coarser than silt. Sand can also refer to a textural class of soil or soil type; i.e., a soil containing more than 85 percent sand-sized particles by mass.The composition of sand varies, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal settings is silica (silicon dioxide, or SiO2), usually in the form of quartz. The second most common type of sand is calcium carbonate, for example, aragonite, which has mostly been created, over the past half billion years, by various forms of life, like coral and shellfish. For example, it is the primary form of sand apparent in areas where reefs have dominated the ecosystem for millions of years like the Caribbean.

Sand is a non-renewable resource over human timescales, and sand suitable for making concrete is in high demand.

Shallow foundation

A shallow foundation is a type of building foundation that transfers building loads to the earth very near to the surface, rather than to a subsurface layer or a range of depths as does a deep foundation. Shallow foundations include spread footing foundations, mat-slab foundations, slab-on-grade foundations, pad foundations, rubble trench foundations and earthbag foundations.


Silt is granular material of a size between sand and clay, whose mineral origin is quartz and feldspar. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension with water (also known as a suspended load) and soil in a body of water such as a river. It may also exist as soil deposited at the bottom of a water body, like mudflows from landslides. Silt has a moderate specific area with a typically non-sticky, plastic feel. Silt usually has a floury feel when dry, and a slippery feel when wet. Silt can be visually observed with a hand lens, exhibiting a sparkly appearance. It also can be felt by the tongue as granular when placed on the front teeth (even when mixed with clay particles).

Thaw depth

In soil science, the thaw depth or thaw line is the instantaneous level down to which the soil has warmed to zero degrees celsius. The active layer thickness is the maximum thaw depth over a period of two years.

The layer of soil over the thaw depth is called the active layer, while the soil below is called permafrost.

The term frost front refers to the varying position of the thaw line during the periods of freezing/thawing.

The knowledge of the thaw depth is important for the two major reasons: its influence on the ecology and on construction (buildings, pipelines, roads, etc.). These influences are mediated by the effects of the dynamics biological, pedologic, geomorphologic, biogeochemical, and hydrologic processes in permafrost.

In ecology, roots of plants cannot penetrate beyond the active layer, which places restrictions on which plants can grow in permafrost.

In construction, the thaw depth is a major factor in ensuring the structural integrity of the objects in question.

The primary factor that determines the thaw depth is the maximal air temperature. The soil type is another important factor: coarser textures of the parent material have higher thermal conductivity, and, e.g., sandy soils have much deeper thaw line than clays. Yet another factors are the vegetation and the percentage of the soil organic matter, which influence the bulk density of the soil, and hence thermal conductivity.


Thermosiphon (or thermosyphon) is a method of passive heat exchange, based on natural convection, which circulates a fluid without the necessity of a mechanical pump. Thermosiphoning is used for circulation of liquids and volatile gases in heating and cooling applications such as heat pumps, water heaters, boilers and furnaces. Thermosiphoning also occurs across air temperature gradients such as those utilized in a wood fire chimney or solar chimney.

This circulation can either be open-loop, as when the substance in a holding tank is passed in one direction via a heated transfer tube mounted at the bottom of the tank to a distribution point—even one mounted above the originating tank—or it can be a vertical closed-loop circuit with return to the original container. Its purpose is to simplify the transfer of liquid or gas while avoiding the cost and complexity of a conventional pump.


Thixotropy is a time-dependent shear thinning property. Certain gels or fluids that are thick, or viscous, under static conditions will flow (become thin, less viscous) over time when shaken, agitated, sheared or otherwise stressed (time dependent viscosity). They then take a fixed time to return to a more viscous state.

Some non-Newtonian pseudoplastic fluids show a time-dependent change in viscosity; the longer the fluid undergoes shear stress, the lower its viscosity. A thixotropic fluid is a fluid which takes a finite time to attain equilibrium viscosity when introduced to a steep change in shear rate. Some thixotropic fluids return to a gel state almost instantly, such as ketchup, and are called pseudoplastic fluids. Others such as yogurt take much longer and can become nearly solid. Many gels and colloids are thixotropic materials, exhibiting a stable form at rest but becoming fluid when agitated. Thixotropy arises because particles or structured solutes require time to organize. An excellent overview of thixotropy has been provided by Mewis and Wagner.Some fluids are anti-thixotropic: constant shear stress for a time causes an increase in viscosity or even solidification. Fluids which exhibit this property are sometimes called rheopectic. Anti-thixotropic fluids are less well documented than thixotropic fluids.


A trench is a type of excavation or depression in the ground that is generally deeper than it is wide (as opposed to a wider gully, or ditch), and narrow compared with its length (as opposed to a simple hole).In geology, trenches are created as a result of erosion by rivers or by geological movement of tectonic plates. In the civil engineering field, trenches are often created to install underground infrastructure or utilities (such as gas mains, water mains or telephone lines), or later to access these installations. Trenches have also often been dug for military defensive purposes. In archaeology, the "trench method" is used for searching and excavating ancient ruins or to dig into strata of sedimented material.

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