How much does frozen ground heave? Terrain with high water tables and particularly expansive soils such as peat or clay often suffer from frost heave and damage buildings. It’s not uncommon to see a deck or shed move as much as 7 or 8 inches, and in some cases much more than that, even up to two feet.
How much does frozen ground heave?
How much does frozen ground heave? Terrain with high water tables and particularly expansive soils such as peat or clay often suffer from frost heave and damage buildings. It’s not uncommon to see a deck or shed move as much as 7 or 8 inches, and in some cases much more than that, even up to two feet.
When does the ground freeze?
So officially, the ground freezes when the water in the ground becomes ice. Frost Depth (or the frost line) is the deepest point to which ground water will freeze.
What is a ground frost heave?
Ground frost heave, at its most simple, happens when ground water in cold climates changes from a liquid to a solid.
Why does the ground heave when water freezes?
The actual vertical displacement is far in excess of the expansion that occurs when water freezes. Heaving occurs when the right combination of fine grain soil, soil moisture and soil temperature exists. As the mean air temperature drops in the fall of the year, the surface of the ground will freeze.
How cold does it have to be for frost heave?
32°FFrost heave takes place when the temperature of saturated sub-grade soil below the concrete floors of a cold storage area dips below 32°F causing pockets of moisture within the soil to freeze.
Is soil lifted up when the ground freezes?
Water is drawn from unfrozen soil to the freezing zone where it attaches to form layers of ice, forcing soil particles apart and causing the soil surface to heave. Without physical restraint there is no apparent limit to the amount of heaving that may occur.
How strong is frost heave?
How much does frozen ground heave? Terrain with high water tables and particularly expansive soils such as peat or clay often suffer from frost heave and damage buildings. It's not uncommon to see a deck or shed move as much as 7 or 8 inches, and in some cases much more than that, even up to two feet.
How much does soil expand when it freezes?
Water-saturated soils, where clay is involved, can hold up to two-thirds water by volume, and water expands by 8 percent when it freezes. So the total volume of soil can expand by as much as 5 percent during freezing conditions. Unlike ice lenses, this freezing soil expansion exerts force in all directions.
How much does ground heave in winter?
The amount of frost heave can be tremendous. In one case, a seven-story building heaved 2 to 3 inches. Vertical ground movements of 4 to 8 inches are common and as much as 24 inches have been reported. Variations in the amount of heave, due to different soil and water conditions, can crack structures easily.
How much does ground rise in winter?
When ground water freezes its volume expands by 9%. For this reason, pressure sensitive structures, such as water and sewer lines, need to be buried below the frost depth to avoid ruptures.
Does homeowners insurance cover frost heave?
Frost heave – Generally NOT covered This process can raise, shift and damage foundations and is normally an excluded peril in insurance policies.
Does gravel prevent frost heave?
Gravel soil itself is generally considered as free from frost heaving. Therefore, it is usually used as soil base construction material in seasonally frozen regions. However, when gravel soil contains a certain amount of fine grained soil, especially silt soil, then frost heaving will still occur.
Does concrete settle after frost heave?
When the moisture in the soil freezes, it expands as all water does. This expansion pushes up against the concrete slab and raises it. Frost heave is fairly typical in our weather climate. In many cases the slab will settle back down after the frost leaves the ground and return to its original position.
Which type of soil has the highest potential for frost heave?
Some types of soil are more prone to frost heaves than others. Polli Construction says clay soils are most vulnerable to freezing due to their higher moisture content. Erie Insurance, a company in Erie, Pa., says loamy and silty soils also tend to freeze during the winter.
Does ground thaw from top or bottom?
We still have a small constant heat coming up from below trying always to thaw the ground, but the real thaw comes more quickly from the top down.
What type of soil is most susceptible to frost heave?
Silty soilsSilty soils are frost-susceptible because their small particle size and high porosity support high moisture contents, while their permeable nature and high hydraulic conductivity encourage capillary action. Thus soils with high silt content promote the formation of segregated ice lenses and frost heaving.
What happens to soil after they freeze?
As soils freeze, ice blocks the soil pores, greatly diminishing the permeability of the soil. This is aggravated by the tendency of water to migrate to the freezing front, causing elevated ice content and frost heave. Soil freezing and thawing also plays a role in a variety of other environmental processes.
What happens to soil when its cold?
Once the surface of the soil dips below 32 degrees Fahrenheit (0 degrees Celsius), water in the ground will start to freeze. "The first layer of the soil to freeze will be right at the surface," said Tiedeman. "Over time, as the air gets colder and colder, the soil will continue to freeze deeper and deeper."
What happens when soil freezes?
As water in the ground becomes solid, it expands and squeezes soil materials together. Ice also pushes soils upward, causing the ground to heave. Freeze-thaw cycles can severely damage plants by pushing them out of the ground and by ripping and pinching their roots apart. What's Happening Under Your Feet?
Does ground thaw from top or bottom?
We still have a small constant heat coming up from below trying always to thaw the ground, but the real thaw comes more quickly from the top down.
How much heat does it take to freeze soil?
The rate at which soil freezes is dependent upon its thermal properties, moisture content, and the ambient air temperature. Of these, probably the most important is the amount of water to be frozen, since it requires 144 heat units (Btu) to freeze each pound of water and by comparison only about 0.20 heat units to change the temperature of a pound of dry soil by 1°F. The density, conductivity of the soil particles and water content all influence the over-all thermal conductivity of soil. Because clay particles have a higher insulation value than silt or sand particles and since clay soils normally hold more moisture than silts and sands, the depth of frost penetration is usually greater in silt and sandy soils (light-textured soils) than in clays and silty clays (heavy-textured soils).
What is frost heaving?
Swedish literature dating back to the 17th century indicates that the uplifting of boulders in the field and the breaking of plant roots in the winter were associated with frost heaving. At first, frost heaving of the soil was thought to result from the expansion of water on freezing.
Why do buildings have differential heaving?
A detached unheated building located on frost heaving soil may show no signs of distress owing to the fact that the foundation has been raised uniformly so that no stresses have been induced in the structure. Because of the non-uniformity of soil and other factors such as variable snow cover, it is more usual, however, to have differential heaving. This may also occur where the building has supports carried on footings located inside the structure. Due to the protection provided by the building, the penetration of frost under the interior column footings may be less than that under the perimeter footings. Under these circumstances there is a possibility that differential movement will occur.
How to prevent frost heaving?
Since it is seldom economically possible to control soil temperature, frost heaving is usually prevented by replacing the fine grain soil with a coarse granular material. Soil moisture can also be controlled by careful attention to drainage, so that the extent of frost heaving is greatly reduced.
Why is frost more likely to occur in clay soil?
Because clay particles have a higher insulation value than silt or sand particles and since clay soils normally hold more moisture than silts and sands , the depth of frost penetration is usually greater in silt and sandy soils (light-textured soils) than in clays and silty clays (heavy-textured soils).
Why does the freezing plane prevent the ice lens from growing?
At the same time the freezing plane is prevented from penetrating further into the unfrozen soil because of the heat made available from the water as it freezes.
What happens when ice crystals grow?
The present concept is that growing ice crystals draw water from the surrounding soil and develop into ice lenses. Ground Freezing and Frost Penetration. When wet soil freezes, the main process is the physical change of soil water from liquid to solid that turns the soil into a hard mass resembling concrete.
How to measure ground freezing?
Air temperature records can be used to gauge the severity of ground freezing by using the degree-day concept. (If the daily mean air temperature is 31F this will be one degree-day.) The "Freezing Index" is simply the accumulated total of degree-days of freezing for a given winter.
How is depth of freezing determined?
Depth of freezing is largely determined by the rate of heat loss from the soil surface. Besides the thermal properties of the soil, this heat loss depends upon such climatic variables as solar radiation, snow cover, wind, and air temperature, which is the most significant.
How does water affect the freezing zone?
Water is drawn from unfrozen soil to the freezing zone where it attaches to form layers of ice, forcing soil particles apart and causing the soil surface to heave. Without physical restraint there is no apparent limit to the amount of heaving that may occur. (Movements in excess of 4 in. developing under basement floors in only three weeks have been recorded.)
Why is water needed in the freezing plane?
Water must be available in the unfrozen soil for movement to the freezing plane where the growth of ice lenses occurs. A high groundwater table with respect to the location of the ice lenses will therefore favour frost action. Where proper drainage is prescribed water can be prevented from reaching the freezing zone in frost-susceptible soils.
What is the term for the action of frost on a foundation?
A different form of frost action, called "adfreezing, " occurs when soil freezes to the surface of a foundation. Heaving pressures developing at the base of the freezing zone are transmitted through the adfreezing bond to the foundation, producing uplift forces capable of appreciable vertical displacements. If constructed of concrete block a basement wall may fail under tension and part at a horizontal mortar joint near the depth of frost penetration.
What are the three conditions that must be met for frost action to occur?
For frost action to occur three basic conditions must be satisfied: the soil must be frost-susceptible; water must be available in sufficient quantities; and cooling conditions must cause soil and water to freeze. If one of these conditions can be eliminated, frost heaving will not occur.
How to prevent frost damage?
The conventional approach to the design of foundations to prevent frost damage is to place the foundation beyond the depth of expected maximum frost penetration so that the soil beneath the bearing surface will not freeze. This measure alone, however, does not necessarily prevent frost damage; if the excavation is backfilled with frost-susceptible soil it may lead to damage from adfreezing. Depths at which foundations should be placed are normally determined by local experience, as incorporated in building bylaws, but in the absence of such information the correlation shown in the preceding chart can be used.
What happens when ground water freezes?
Ground frost heave, at its most simple, happens when ground water in cold climates changes from a liquid to a solid. Water expands by 9% when it freezes, so for any structure that is seated above the frost line – be it a deck, shed, slab on grade or a basement foundation, when expanding soils forces it upwards, ...
How much force can a building exert when it freezes?
A force of 19 tons per square foot has been measured with one seven-story reinforced concrete frame building on a raft foundation that heaved more than 2 inches. But, preventing frost heaving is actually a breeze as long as you design properly, and here we tell you how.
What problems can frost heaving cause?
The pressure of frost heaving can crack basement walls - especially when built of CMU or brick - or with the lifting forces of frost heave caused by " adfreezing ," which occurs when soil freezes to the surface of a foundation.
Why is frost protection important?
Frost protected foundations - essential in cold climates. Protecting homes and buildings in cold climates from structural damage caused by frost heave is essential for durability. In most parts of Canada and the northern United States, the ground freezes during the winter months to a depth of several feet.
How does adfreezing work in a basement?
The heaving pressures developing at the base of the freezing zone are transmitted through the adfreezing bond to the foundation, producing uplifting and separating forces capable of pulling CMU apart by vertical displacement of a horizontal mortar joint near the depth of frost penetration. This is very important to consider when insulating a basement or insulating a crawlspace in an older home from the inside.
Why does ice build up?
The build-up of ice happens largely because water in the unfrozen soil below gets drawn up into the freezing zone and attaches itself to the existing frost crystals to form ever thickening layers of ice. The key phrase for this phenomenon is " ice segregation". This is what causes the expansion that forces soil particles apart, and is what causes the ground to heave upwards. But did you really need to know that? Yep. And you can thank me in the comments section after you pull out that little nugget at a dinner party and impress your friends.
What causes frost heave?
It is mostly thought that the upward expansion of existing moisture in soil is what causes frost heave, but it’s slightly more complicated. So, for building nerds who want the real skinny on what’s going on, it’s a bit like this -
How deep is the freezing plane?
The depth to which they can potentially extend in any given region is the frost line. Frost lines range from a few inches in Florida to more than 6 ft. in the northern United States.
What exactly is frost heave?
Frost heave occurs when freezing temperatures penetrate the ground, causing subsurface water to form ice structures that displace the soil along with anything that rests on or in that soil. While it was once thought that frost heave happens because water expands as it freezes, the process is actually more complicated, involving not only expansion due to freezing, but also the accumulation of additional layers of ice as liquid water is drawn up from below the frost line.
How does freezing water work?
When freezing temperatures penetrate the ground, water trapped in voids in the soil forms ice crystals along the frost front. As it solidifies, this water expands by about 9%. In addition, the freezing process desiccates the surrounding soil, drawing unfrozen water from below the frost front through capillary action and vapor diffusion. This water freezes to the ice crystals that have formed above, thickening it to create an ice lens.
What are the elements that can cause frost heave?
Mitigation typically involves removal of one of the three elements (frost-susceptible soil, freezing temperatures, or water ) required for frost heave to occur. Here’s how it works.
How to prevent ice from gripping concrete?
Frost heave also can be controlled by backfilling around piers with gravel to promote drainage, using a sleeve to prevent ice from gripping the concrete, or pouring footing bases that resist upward movement.
What structures can freeze in winter?
In any region where the ground freezes in wintertime, all structures that contact or penetrate the soil –foundations, basements, piers, retaining walls, patios, driveways , and more–are susceptible to damage if they aren’t built properly. Local codes will dictate the requirements, which is one of the primary parameters that will ensure ...
Why does a basement need less moisture?
This outward heat loss pulls moisture away from the foundation walls. Because moisture is required for adfreezing, less moisture means the frozen soil has a less tenacious grip on the foundation.
What is the cycle of freezing and thawing in the soil?
The cycle of freezing and thawing in the soil and the formation of seasonal ice deep in the ground create an upward movement of objects in the soil. The freezing and thawing essentially squeeze the soil, causing solid objects like rocks and boulders to heave upward toward the surface.
How does frost heave affect soil?
Although it may be easy to say that frost heave is simply the result of the expansion of frozen water, however, the force of frost heave is greater than that of frozen water. When water freezes, it expands to increase its volume by 9%. Ground soil with a 50% water content would expand by only 4.5%. This creates a frost heave of only about a half an inch per vertical foot of soil. Assuming that the soil is squeezed in just one direction, upward, this accounts for a very slow emergence of boulders. But any farmer can tell you that the rocks emerge at a quicker pace. Other factors are involved that increase the upward thrust.
What are the factors that cause frost to heave?
For frost heave to occur, three factors must be present: freezing temperatures, a particular type of soil, and plenty of water.
What happens to ice lenses when soil freezes?
When the soil freezes and thaws, multiple ice lenses can form, stacked on top of each other with a thin layer of frozen soil between them. The ice itself is composed of many filament-like ice crystals that form and grow parallel to the direction of heat flow. It is this growth of the ice crystals in the ice lens, Taber proved, ...
What happens every spring when farmers plow their fields?
Every spring, when farmers plow their fields, they find large boulders that weren’t there the previous year. Does the boulder fairy deliver these to the farmer? Nope! The truth is, the rocks have always been there, hiding deep in the soil out of reach of the plow blade. Thanks to the process of frost heaving, every spring sees the surface emergence of new rocks, stones, and boulders.
What is the end result of the emergence of rocks and boulders in farm fields?
The surface emergence of rocks and boulders in farm fields is the end result of this complex and logic-defying behavior of water within porous, glacial soil. As the water is pulled upward by the formation of ice lenses, it brings with it solid material, like rocks, that are forced to the surface by the cycle of freezing and thawing. It is not quite as dramatic as rock-planting sprites and leprechauns, but the power of freezing water, while grounded in science, is almost as magical.
Who was the Swedish geologist who studied frost heave?
Also in the 1930s, concurrent with Taber’s research on frost heave, a Swedish geologist named Gunnar Beskow, working for the Swedish Institute of Roads, became his research into frost heave, focusing on the composition of soil. He observed that the size of the soil particles impacted the degree of frost heave.
How to keep soil from grabbing on footing?
One step that can be taken to help prevent soils from grabbing on to the footing is to use waxed cardboard tubes for the footings, often referred to as sonotubes . The Family Handyman web site has a great cutaway photo of a footing with one of these tubes, used with permission below.
How do deck footings heave?
How Deck Footings Heave. When a deck is attached to a building, the part of the deck that gets supported by the earth needs to have proper frost footings. The most common deck footing is basically a big chunk of concrete poured in to a hole in the earth. The goal is to have this chunk of concrete go deep enough in to the ground ...
What happens when you break a footing in half?
When expansive soils grab on to the walls of a footing and pull it up, the bell at the bottom will hold the footing in place until the pressure exerted by the frost exceeds the tensile strength of the concrete. Once that happens, the footing will simply break in half.
How deep should a footing be in Minnesota?
The Minnesota State Building Code requires footings to be a minimum of 42” deep in the southern part of the state, and a minimum of 60” deep in the northern part of the state. The diagram below shows the dividing line. While footings need to be deep enough in the soil to prevent frost heave, the depth of the footing is only one part of the equation.
Does snow reduce frost depth?
There’s no magic number. When there is a lot of snow on the ground, the snow acts like a layer of insulation and reduces the frost depth. When it’s a winter with very little snow, like the type Minnesota experienced in 2011-2012, the frost depth will be much deeper than usual.
Can pier footings break in half?
Once that happens, the footing will simply break in half. When you consider the relatively low tensile strength of concrete and the tremendous amount of force exerted by frost, it’s easy to understand how pier footings can break. One step that can be taken to help prevent this is to use rebar inside the footings.
What is the impact of frost heaving on the Earth?
Frost heaving can wreak havoc with houses, barns, sheds, roadways, concrete slabs, basically anything that's connected to the Earth in a place where the ground freezes. Just as the phrase implies, the frost heaves, or lifts, things up. The problem is, the lifting may not be equal around the structure.
What are Frost Heaves?
Frost heaves are a show of force that happens quietly, covertly and with little warning if you've never been harmed by them.
How does frost affect soil?
The frost can drive deeply into soil that's adjacent to a natural spring. Subsurface water that continues to flow through the winter under the soil feeds the ice lenses under the surface that jack up the soil like a ratcheting auto jack that lifts a car when you have a flat tire.
Why does my soil heave in the winter?
Water in soil combined with below-freezing temperatures is what causes frost heaves. Different soil types are more susceptible to frost heaving. Obviously, those soils that can hold more water will react more vigorously to frost. This means sandy, loamy soils can lift higher, on average, than dense clay soils. Where I now live in New Hampshire, the soil is very sandy and loamy. Believe me, it really lifts up in the winter.
Can snow cover drive frost into soil?
If these conditions persist, the frost can be driven deeply into the soil. Snow cover actually acts as an insulator . If it had snowed early and heavily in the season, the frost might be fairly shallow in the soil now. The frost can drive deeply into soil that's adjacent to a natural spring.
Can concrete be lifted from frost?
If you keep the soil pretty dry as you head into winter, there is little fuel to feed the ice lenses that create the frost heaves. Concrete slabs that are prone to lifting from frost should contain plenty of reinforcing steel.
