Frozen Ground and the Frost Line: How and Why it Freezes

How Deep Does the Ground Freeze in Winter?

Ground frost occurs when the ground contains water, and the temperature of the ground goes below 0° C (32° F). More than half of all the land in the Northern Hemisphere freezes and thaws every year, and is called seasonally frozen ground. One-fourth of the land in the Northern Hemisphere has an underground layer that stays frozen all year long. If the ground remains frozen for at least 2 years in a row it is called permafrost

What causes ground frost?

When ground is frozen solid, the water between the rocks, soil, and pebbles, and even inside the rocks, has frozen and becomes pore ice. So officially, the ground freezes when the water in the ground becomes ice.

Frost Depth

Frost Depth (or the frost line) is the deepest point to which ground water will freeze. Frost depths vary depending upon the frost line in each location and can have a great impact on many construction practices. For example, any crews digging to access utility lines or preparing ground for a concrete pour will need to be aware of their local frost depth.

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. When water turns into ice, it can expand with great force and cause the ground to swell. In areas with a cold winter season ground frost can damage roads. For example, water turning to ice under roads sometime creates frost heave. The expanding ice pushes up the road and creates a hump, which later, after a thaw, will create potholes  and sunken sections in a roadway.

The frost line varies depending on the length of time the air is cold. The longer the cold period, the deeper the ground will freeze. But the depth of frozen ground is limited, because Earth is warm deep inside.

What Affects the Frost Line?

Most of Earth’s heat comes from the Sun (Figure 1). The ground stores a lot of the Sun’s heat and reflects the rest into the air. Snow and ice are light colored and reflect more heat away. Ocean water and bare ground reflect less heat, instead absorbing it. This transfer of heat between the ground and the air is called the surface energy flux.

energy balance diagram

Figure 1. This diagram shows how the Earth’s atmosphere and the ground reflects and absorbs the Sun’s energy.

Credit: NASA Atmospheric Science Data Center

Heat is also coming from the inside of the Earth. The Earth’s core is very hot, and its heat moves towards the surface. Heat from volcanoes, rivers, lakes, and other sources can also spread through the ground. This heat keeps some areas unfrozen, even though surface temperatures are low.

In general, deeper permafrost is very old. One researcher found that the deepest part of the permafrost underneath Prudhoe Bay, Alaska, is more than 500,000 years old.

The Temperature Gradient

When the temperature of the ground drops below 0° C (32° F), it freezes; however, the ground temperature can be different from the temperature of the air above it. This temperature gradient means that layers deep within the ground may be colder or warmer than layers near the surface.

The top layer of ground may respond to conditions on the surface, but the layers below may not change as quickly. On a warm summer day, the surface of the ground absorbs heat and becomes hotter than the air. But the temperature a few feet underground may be much lower than the air. It is the opposite in the winter; the surface of the ground cools, but the layer deep underground may stay warmer than the surface. The upper layer of ground stops heat from moving between the cold air and the deeper layers of the ground, insulating itself.

How does the local landscape affect ground frost?

Ground frost is affected by more than just temperature swings, seasonal changes, and location. Snow, soil, plants, and other aspects of the local landscape also affect frozen ground.

Snow

A thick layer of snow acts like a blanket so that heat does not leave the ground. Only a thin layer of ground will freeze under a thick layer of snow.

Soil type

Some soils freeze more easily than others. Light-colored soils freeze sooner and stay frozen longer than dark soils. Light-colored soils and rocks reflect sunlight, keeping the ground cooler. Loose soils like sand have more space for water and ice forms more easily. Dense soils with small particles do not have as much space for water. Clay, for example, does not freeze as easily as sand.

Peat

Peat forms when dead plants do not fully decompose. The ground under peat is usually colder than ground not covered by a peat layer.  In the winter, peat freezes and allows heat to leave the ground. Because the heat escapes, more frozen ground and permafrost form.

Plants

In the summer, plants keep the soil underneath them cooler because they block some sunlight from reaching the ground. Evergreen trees especially keep the ground cooler. Evergreen trees do not lose their leaves in the winter. This means that the trees block sunlight from warming the ground. Plus, their branches block snow from reaching the ground underneath. The bare ground loses heat more easily. Permafrost often forms under evergreen trees.

Slopes

Hillsides and mountain slopes can affect frozen ground and permafrost. If a slope gets more sunlight because of the way it faces, the ground will be warmer and will be less likely to freeze. In the Northern Hemisphere, slopes that face south, towards the Sun, get more sunlight than shady slopes that face north. The opposite is true in the Southern Hemisphere.

Steep slopes are likely to contain frozen ground. The steepness of the slope affects how much sunlight it gets. Steep slopes do not get as much direct sunlight, so they are colder. Steep slopes do not hold snow cover very well, so the bare ground loses more heat. Wind direction also affects whether frozen ground forms. If a slope faces into the wind, the ground will lose more heat. Plus, the wind will blow snow away making the ground even colder.

Lakes and rivers

Lakes and rivers are sources of heat in cold places. The water is warmer than the surrounding air and can keep the ground beneath it warmer in the winter. Lakes and rivers might not have frozen ground under them. Or, they might have a thicker active layer compared to nearby land.

Powerblanket Ground Frost Solutions

“Your blankets are absolutely excellent. Thanks to the Powerblankets, we were able to quickly thaw the ground and complete our job. In fact, we estimate a savings of 10 hours per site equaling a savings of $5,000 already. Calculating this to our thousands of sites, the savings is huge! We are excited about the time and money Powerblanket has saved us and look forward to future savings.”

— Kim Herman OSP/COEI Operations Manager Precision Utilities Group

The frost line is a reality many industrial companies must face.  The high watt density in Powerblanket ground thawing products helps tackle the difficulty of thawing ground in harsh climates.  Use a Powerblanket ground heater to save time, money, and stress.  

frozen ground being thawed

 

Tracks on Fire: Keeping Train Tracks Thawed

Winter has a habit of freezing progress in its tracks. Snow and ice can make roads unsafe to travel on, bury runways, and cause fuels to thicken. Even railroads can’t escape the damage done by Jack Frost.

In fact, railroads have to deal with some of the most dangerous effects of snow and ice. Track switches that freeze up lead to costly delays, as well as the potential for derailments. Keeping tracks thawed and switches ice-free is critical for operating a safe and efficient railroad.  

The Long Island Railroad uses a variety of methods to keep their switches from freezing, even by setting their rails on fire. According to the Long Island Railroad blog, electricity, natural gas, kerosene oil and a hydrocarbon oil called Hexane, are used every winter across the railway to ensure switches are thawed and operational.

rail heating
Gas heating along a rail line keeps the tracks thawed and operational.

These days on the LIRR, most switch heaters are electric. They are made up of high resistance metal bars that are bolted to the sides of the running rail. One end is grounded to the running rail and the other end is tied to the third rail through a knife switch in a little box. Most are activated onsite, but there are some that are remote controlled.

rail heating
Workers monitor tracks as they thaw with help from natural gas.

The gas powered switch heaters are older: vestiges from an age when electric power was expensive and unreliable and gas was cheap. The gas powered heaters would keep a place like Jamaica open even if electric power failed. Today the gas heaters use natural gas that is provided by the utility companies (at one time they used manufactured gas from coal). The gas to these heaters is supplied by a one-and-a-half inch pipe with a globe valve down in a pit near the switch. A mechanic from the LIRR’s Buildings and Bridges department turns on the gas and lights it with a fuse. Then the winds blow it out.

rail heating
Some railroads use a snowblower to thaw rails. The heat blast eliminates ice build up, but the process is slow.

These days it is the gas heaters which are less than reliable; they blow out in high wind and have to be re-lit (a tricky task in the middle of rush hour).

The LIRR still also uses the really old “switch pots” which are filled with kerosene and burn a wick under the switch points. These are maintained by the track department. Trackmen work through the storms filling and lighting these.

And no story about switches and ice can be complete without mentioning “switch oil.” To thaw out frozen switches, trackmen use Hexane, a hydrocarbon oil that is dumped along the rail from a long snouted can that looks like a flower watering can. Another trackman follows the first with a blazing broom that was soaked in the stuff which he uses to light up the oiled switches. The goop burns for fifteen minutes, effectively de-icing the frozen switch. 

ground thawing warming blanket
Ground thawing blankets eliminate the need for costly heating systems and are easily portable.

There is an easier way, of course, to keep rail switches thawed during winter storms. Introducing: Powerblanket Extra-Hot Ground Thawing Blankets. These provide a cheaper, more efficient method to prevent delays that come from iced tracks.

Simply plug the blanket into an electrical source, and the thawing begins. With a preset of 150 ͒ F, the rapid thaw blanket is a maintenance-free heating solution that reduces downtime, eliminates headaches associated with frozen ground, and saves money.

Reliance on manual labor or antiquated heating methods can stay where they belong: in the past. Use the Extra-Hot Ground Thawing Blankets to keep rail switches thawed, passengers safe, and trains on time.

Concrete Curing in Freezers

An Atypical Concrete Job

Concrete curing in freezers is a unique experience. Walk in freezer concrete floor construction requires a specially cured solution that can handle constant sub-freezing temperatures. This concrete is also required to be strong enough to support heavy equipment traffic from forklifts and other machinery. These freezers are a crucial part of the cold chain that protects the safety of cold products (such as meat, ice cream, medicine, cadavers, liquid oxygen, and more) during transport and storage. Walk in freezer failure is an expensive, and dangerous broken link in that refrigeration cold chain. When the structural integrity of a walk in freezer is jeopardized, the contents within can spoil, creating a huge employee and consumer safety hazard. Not all walk in freezer failures are preventable. However taking a few extra precautions during freezer concrete floor construction can prevent costly downtime and repairs.

Walk in Freezer Concrete Floor Repair
Image taken from www.garonproducts.com

Prepare The Ground

There are a number of layers that need to be in place before pouring to protect your concrete from freezer floor heave. Freezer floor heave occurs when the moisture in the soil freezes and expands below your slab. If the soil then begins to thaw, it will also sink and settle, causing massive damage to the concrete above. Protective layers of insulation, vapor barriers, mud-slabs, and sub-slab glycol heating prevent the soil from freezing and swelling below your concrete floor.

Maintain The Mix

Ensure your mix of concrete doesn’t contain too much water. An overly wet mix is likely to cause cracking due to shrinkage. The water can also freeze within the concrete if it’s not cured enough by the time the freezer begins operating. Your concrete freezer floor may appear set on the surface, but the lower layers will not be strong enough to bear weight or thermal stress. 

Ensure The Cure

Walk in freezer floors need to endure constant walking foot traffic, heavy stacks of pallets, and forklifts. Your concrete needs all the compressive strength it can get to withstand such thermal and physical stress. Using concrete heating blankets, instead of traditional insulated blankets, ensures your concrete floor cures faster and to a stronger PSI rating.

Seal The Deal

The United States Dairy Association (USDA) has a zero-tolerance policy regarding leaks within a freezer. Frozen food requires storage at 0°F, as “freezing to 0° F inactivates any microbes — bacteria, yeasts and molds — present in food.” Leaks allow moisture to invade the freezer, which can trigger mold and other harmful pathogen growth. Properly sealing concrete floors in a walk in freezer protects your slab, prevents leaks, and maintains USDA safety compliance requirements. 

Restoring Concrete Freezer Floors

Concrete floor damage, like cracking or chipping, is triggered by a number of factors such as: forklift accidents, threshold damage, sub-floor heating replacements, and freezer floor heave. Our friends at Concrete Mender warn of several concrete repairing challenges:

Frost

Frozen moisture in the concrete will act as a barrier between the repair material and the pores of the concrete. Most repair materials will try to bond to the frost coated concrete. When the temperature increases, the frost melts and so does the bond.

Ambient Temperatures

Mixing epoxies or mortars in the cold is especially challenging. As the temperature decreases, the viscosity of these materials increase making them very difficult to pour, mix and work with. Bucket and drum heaters are an excellent solution to keeping epoxy and mortar warm while waiting to use on a freezer floor.

Powerblanket diagram showing the affect of temperature on fluid viscosity

Curing

Materials used to patch and repair concrete cure much more slowly at cold temperatures. A product that takes 1 hour to cure at room temperatures can take 12 hours to cure in cold temperatures. Some materials may actually freeze solid before they can cure properly. Keeping patching materials warm during the curing process will cut down your cure time and increase their durability. Curing blankets are the most efficient way to ensure your repairs cure quickly and firmly. Curing blankets heat through conduction and have complete surface contact to transfer heat directly where it is needed most.

Concrete Solutions From Powerblanket

There are a lot of elements involved in preparing and pouring a concrete freezer floor. When things go wrong, repairing a damaged freezer floor is just as challenging. Taking extra precautions before, during, and after you pour will ensure your slab is built to last. Powerblanket is here to help. With our wide range of bucket and drum heaters, you can keep your materials warm and ready to use for any repair job. Our concrete curing blankets are the perfect solution for quickly achieving high PSI ratings. With a cure rate 2.8 times faster than conventional insulated blankets, you can be sure to meet project deadlines on time. Contact us to find the perfect solution for all of your concrete needs 855.447.9358 or [email protected] 

Grave Digger Solutions: Unthawing cold ground with Powerblanket

North America experiences a variety of weather patterns during the winter months. However, most of the continent will undergo cold enough temperatures that freeze the upper layers of ground soil.

This can be highly problematic for those needing to dig into the ground during the winter. Projects that normally take a few hours worth of digging now takes days to unthaw and break through the frozen topsoil.

Image taken from www.adventuresincemeteryhopping.com.

Powerblanket’s Ground Thawing Blankets were essential in saving the Hailey Cemetery time and money during the Idaho Winter of 2017. Wayne Burke, maintenance supervisor for the cemetery, said that winter was colder and less wet than years previous, causing the soil to freeze much deeper than normal.

“There’s usually six inches of snow on the ground,” Burke said, adding that the snow acts as a layer of insulation, preventing the ground from freezing as much. “It always worked out great. But last year it got really cold and there was no snow.”

Burke knew he needed solutions fast to meet the demand of the cemetery’s burial service schedule. He reached out to Powerblanket, and within two days of ordering, received his Ground Thawing Blanket.

“You guys sent it just in time. I used it the first day, and only had it on for 12 hours. It still worked,” he said. “A few weeks later, I needed it again. We also loaned it to another cemetery and they were really happy with how it worked too.”

In years prior Burke said he used propane torches to thaw the soil before digging. In addition, the cemetery landscaping had to be torn up and replaced after each dig.

“It worked perfect,” he said. “It thawed about 14 inches down into the ground. The grass greened up and I was able to cut it up into strips and roll it up. The sod was in good shape and I stored it in our garage. After the burial we put the dirt back in a rolled the sod back out. Normally we tear the sod up and throw it away and replant it in the springtime.”

Burke said the Ground Thawing Blanket was exactly what he needed to break through the tough winter soil, saving him hours of manual labor and nearly $100 in landscaping.

“I was really happy with it, and we’ll be using it again this year,” he said.

5 Helpful Tips for Winter Construction Efficiency

5 Tips for Winter Construction

Working outside during the cold winter months presents many obstacles; however, some jobs will not wait for better circumstances. Below are some tips and solutions to improve winter construction.

1) KEEP YOUR EMPLOYEES SAFE

Train your employees in proper winter construction precautions.  Encourage everyone to wear layers of loose-fitting clothing, to stay dry, and to protect from the wind and sun with gloves, hats and sunscreen.  If conditions become too cold/dangerous, employees should have access to shelter.

On the work site, remove ice and snow regularly to prevent slips and falls.  This can be a full-time job depending on the weather.  The act of shoveling snow can also be extremely strenuous, especially for those individuals who do not engage in regular cardiovascular activity. According to the Cleveland Clinic, approximately 11,000 people seek shoveling-related hospital treatment each year for injuries (93%) or cardiac issues (7%). To save time, energy, and your employees health, use Summerstep heated safety mats to keep the walkways on your construction site clear.

Summerstep Snow Melting Mats

  • ,  Protect personnel from winter weather conditions and keep stairs, doorways, walkways, and ramps free from snow and ice
  •   Prevent slips and falls
  •   More convenient than shoveling snow
  •   More effective for snow and ice melting than harsh chemicals (less damaging to the environment, reusable, won’t damage concrete or other flooring surfaces)
  •   Will melt approximately 2 inches of snow per hour when operating
  •   40 Watts/Sq ft heated area
  •   The ONLY snow melting mat product made in the USA

 

2) MAINTAIN INTEGRITY OF CONCRETE

Winter construction cold-weather operations aren’t just about safety. While most construction tasks can be carried out in cold weather, some operations, such as concrete work, can take much longer and even fail without proper precautions.

 

If concrete is to reach necessary strength levels, it can’t be allowed to freeze for the first 24 hours after being poured or placed. Sheeting the concrete can ensure the required temperature and moisture necessary for curing, if the weather isn’t too severe.  In severe conditions, supplemental heating systems or enclosures must be brought in to maintain the integrity of the concrete.

 

Powerblanket Concrete Blankets provide a manageable way to cure concrete in the cold weather months, save you time and money, and come in various lengths and sizes. We have you covered.

 

Powerblanket Concrete Curing Blankets

  •   Cure concrete 2.8 times faster than conventional insulated blankets
  •   Produce cold weather concreting strength of 3,925 psi in 72 hours
  •   Maintain moisture throughout hydrating process
  •   Easily installed and removed
  •   Maintain ACI compliance for cold-weather concreting  Certified to UL and CSA standards

 

3) DON’T LET FROZEN GROUND SLOW YOU DOWN

When it’s cold and the ground freezes, the job suffers.  Often prep for winter construction takes longer than the actual job.  Some industrial companies try heating the ground with massive coils or large heating systems, which become expensive and cumbersome. This approach requires rental fees and transporting equipment.  

Powerblanket has considered the difficulties and delays associated with winter construction and cold/freezing temperatures and has created a solution.  With Powerblanket’s patented heating technology you can prep the ground with little to no effort or supervision on your part.

Powerblanket ground thawing blankets have a higher power density and hotter temperature than our concrete curing blankets. The higher power is iideal for ground thawing applications and curing epoxy or resins.

Why Powerblanket Ground Thawing Blankets?

  •   High power density thaws frozen ground quickly
  •   Remove frost prior to concrete pour
  •   Melt snow and ice from roofs, walkways, and construction areas
  •   Easily placed and removed for repeated use in harsh winter weather
  •   Can be used to cure epoxy and resins
  •   Certified to UL and CSA standards

 

4) KEEP MATERIALS WARM

Masonry, roofing, paint, and plaster/stucco materials are all sensitive to cold weather.  Maintaining the integrity of these materials is critical for their success in winter construction.

Powerblanket Hot Boxes save you money by keeping your products from freezing without the risk of overheating. The Hot Box pallet warmer is easily assembled, taken apart. Hot boxes are ideal for cold wea
ther storage, freeze protection, transporting, job site heating, remote location use, and winter roofing. Standard Hot Boxes hold product between 100°F and 120°F (38°C and 49°C) and optional adjustable thermostatic controllers allow temperatures to be precisely controlled.

Powerblanket Hot Boxes:

  •   Quick and easy assembly
  •   Preserve temperature sensitive material
  •   Heat materials and palletized products: adhesives, shingles, paint, caulk, resins epoxies, etc.
  •   Access doors on two sides.
  •   Certified to UL and CSA standards

 

5) USING A PROPANE HEATER

Winter construction professionals often use temporary, propane-powered heating equipment on the jobsite, making it easier to finish projects on time and on budget. In addition to providing more comfortable working conditions, propane-powered heaters can also maintain the ambient temperatures necessary for common tasks like drywall installation or painting. However, like any portable heating device, propane-powered heaters must be used and maintained properly.

When temperatures get too low, the propane will not flow consistently or effectively, and you may lose your heat altogether. Propane-tank efficiency will fall substantially as the temperature drops. As the temperature drops, so does the pressure in your propane tank, and the pressure in your propane tank directly affects the volume of propane you have to work with. Your extraction rate (how quickly and smoothly you can extract propane from the tank) will suffer as well. Without a heating source to assist in the pressure maintenance of your tank, you will have to keep it as full as possible in order to keep it working, even if temperatures are mildly cold.

Powerblanket Propane Tank Heater

Powerblanket has the best propane tank heating solution on the market. These heating blankets will help maintain pressure and efficiency on just about any size tank. All Powerblanket heating blankets are certified to UL and CSA safety standards

Benefits of Powerblanket Propane Tank Heaters:

  •   Increase performance and efficiency of propane tanks
  •   Eliminates unnecessary cylinder refills in cold weather
  •  Even heat distribution in the areas where it is needed most
  •   Save money by optimizing gas and material usage
  •    Certified to UL and CSA standards

 

 

Ground Thawing Blankets: Prep Frozen Ground with Powerblanket

When it’s cold and the ground is frozen, your job suffers. Thaw frozen ground and get back to work quickly with Ground Thawing Blankets from Powerblanket.

Winter is an interesting beast, especially for those who make their livelihood working outside.  Often prep takes longer than the actual job itself.  Powerblanket has considered the difficulties and delays associated with cold and freezing temperatures and has created a solution.  With Powerblanket’s patented heating technology you can prep the ground with little to no effort or supervision on your part. 

Ground Thawing for Commercial Plumbing

A south-central Utah plumber said, “I wish I had known about Powerblanket’s ground thawing blankets a couple years ago.  We had a job in Mount Pleasant that got so cold that we couldn’t dig.  We started laying out thermal blankets every night to avoid the hard freeze that happened overnight.  We had to layer the thermal blankets in order to keep the ground warm enough to work each morning.  Our progress was slow and labored, and we never knew what we would find at the job site each morning.  It would have been so much easier if we had had Powerblankets.”

Some industrial companies also try heating the ground with massive coils or large heating systems, which becomes expensive and cumbersome. This approach requires rental fees, transporting equipment, and a bit more money than the bid allows.  Your ground thawing blanket can be used over and over on any frozen job you have.

The high power density in Powerblanket Ground Thawing Blankets helps tackle the difficulty of thawing ground in harsh climates. This line of Powerblanket flat blankets has a higher power density and hotter temperature than our concrete curing blankets. The higher temperatures are ideal for ground thawing applications and curing epoxy or resins.

Why Powerblanket Ground Thawing Blankets?

  • High power density thaws frozen ground quickly
  • Remove frost prior to concrete pour
  • Melt snow and ice from roofs, walkways, and construction areas
  • Easily placed and removed
  • Can be used to cure epoxy and resins

Learn More Here

Grave Digging and Ground Thawing

We’re gradually approaching warmer weather now, but it’ll still be some time before the ground thaws and makes digging a lot less difficult. That’s why we’d like to introduce you to our Ground Thawing Blankets. For those in concrete, grave digging, utility maintenance, or any other digging / ground-prep-related project, Powerblanket® Ground Thawing Blankets can be a really big help.

image-ground-thawing-blanketsFrom Grave Digging to Concrete Prep

Whether you’re laying concrete or preparing a funeral plot, our ground thawing blankets can make the process a whole lot easier. Powerblanket Ground Thawing blankets help to thaw frozen ground prior to digging. And in the case of preparing ground for a funeral in the winter or early spring, ground-thawing assistance can make the process run a lot smoother. Here are some words from a satisfied customer who used our ground thawing blankets for their business:

“Your blankets are absolutely excellent. Thanks to Powerblanket, we were able to quickly thaw the ground and complete our job. In fact, we estimate a savings of 10 hours per site, equaling a savings of $5,000 already. Calculating this into our thousands of sites, the savings are huge! We are excited about the time and money Powerblanket has saved us and look forward to future savings.”

Our patented blend of technology and our use of durable materials enable us to deliver high watt density throughout the entire area of application, making ground thawing through electrical heat transfer safe and highly efficient. So when it comes to preparing a plot for burial, use our ground thawing blankets to make the task much easier.

Why Powerblanket® Ground Thawing Blankets?

  • High watt density thaws frozen ground fast
  • Quickly remove frost prior to digging
  • Melt snow and ice from ground prior to digging
  • Easily installed and removed
  • Easily transportable
  • Safe and certified to national safety standards

Some Things to Remember

Remember that thawing ground goes a lot faster if you first manually remove as much snow and ice as you can.  If you have a foot of snow, remove it all, then apply the blankets.  A foot of snow can add a day to the process if not removed first.

Secondly, thawing frozen ground through a layer of grass can be problematic.  The grass tends to hold the blanket up and away from the frozen ground, making the thawing process much longer than it would be with bare ground.  If a Powerblanket ground thawing blanket is left in place too long, it WILL kill the turf. So if keeping the turf healthy and intact is the goal, then don’t use a ground thawing blanket. However, if you’re trying to thaw the ground for digging purposes, then remove the grass first.