Frost heave is a result of the freezing and expansion of water in the ground, it manifests as the underlying soil and rocks swelling upwards. Over time, this can affect local plant life, as well as some structures.

How frost heave happens

During the winter months, or in colder climates, as the ground freezes, it creates a thin layer of ice known as an ice lens. This results in more water being drawn through unfrozen soil through a phenomenon known as capillary action

The new water freezes and attaches to the existing ice lens, causing it to grow continuously thicker. This continuous growth of the ice lens pushes the soil and anything on top of it—like roads, foundations, or plants—upward.

How does frost heave damage?

You can see the damage cause by frost heave in the following ways:

• Potholes/cracked pavements: In spring, as the ice lenses melt, the soil becomes saturated and loses its strength. This, combined with the pressure from traffic, can cause road surfaces to crack and form potholes.
• Foundation damage: The upward pressure from growing ice lenses can lift and shift a building’s foundation, leading to structural problems like cracked walls, uneven floors, and doors or windows that no longer close properly.
• Damage to plants: Frost heave can push plants and shrubs out of the ground, exposing their roots to freezing temperatures and drying winds, which can kill the plant.
• Displaced structures: Fences, retaining walls, decks, and even utility poles can be tilted, shifted, or completely pushed out of the ground.

How can I make a retaining wall free from frost heave?

If the correct steps are not taken during the building process of a retaining wall, it will eventually become susceptible to frost heave. Here are the key considerations you have to remember:

     1. Don’t neglect drainage  

Drainage prevents water from building within the retaining wall, often, insufficient or neglecting drainage altogether generally results in a retaining wall failing. The soil directly behind the retaining wall should be replaced with a materiallike crushed stone or gravel.

The next step is to install a perforated drainage pipe at the base of the wall, running horizontally along its entire length. This pipe collects the water that has filtered down through the granular backfill and directs it to a safe outlet, such as a daylight drain or a storm sewer.

To allow water to pass through while keeping fine soil particles from washing into and blocking the drainage pip, install a filter fabric between the soil and backfill.

For taller or solid concrete walls, strategically placed weep holes at the base of the wall provide an additional escape route for water, relieving hydrostatic pressure.

      2. Make sure to go below the frost line

Ensure the foundation of a retaining wall is below the ‘frost line’. This will ensure it remains unfrozen during colder periods.

      3. Opt for interlocking concrete blocks

The dry-stacked, non-mortared design of an interlocking block (like those available from PPC) allows it to move with the ground. When the soil expands, the wall can accommodate this movement by adjusting its position slightly, and then settle back into place as the ground thaws. In contrast, a rigid, mortared wall is more likely to crack under the same pressure.

Signs that frost has damaged your retaining wall

Due to their porous nature, concrete has the potential to be damaged by frost heave. When water seeps into concrete blocks and freezes, it expands by creating immense pressure that can break the material from the inside out. This damage shows up in the following ways:

Spalling and scaling

Spalling is a common sign of frost damage, where the surface of the concrete flakes off in large or small pieces. This can leave the wall looking rough or pitted, and in severe cases, it can expose the gravel and aggregate within the concrete mix. A milder form of spalling is scaling, which is when the top layer of concrete peels off in thin sheets, often starting at the edges of the wall.

Cracking

While a concrete wall can crack for many reasons, frost damage often causes a pattern of small, random cracks. Over time, as water gets into these cracks and freezes, it forces them to grow wider and deeper with each freeze-thaw cycle, accelerating the wall’s decay.

Pop-outs

These are small, cone-shaped pits that appear on the surface of the wall. They’re caused by a piece of porous rock or stone (aggregate) that’s near the surface. Water gets into that piece of rock, freezes, and creates enough pressure to pop off the thin layer of concrete covering it.

Crumbling

In the most severe cases, a concrete wall can begin to crumble and turn into a sandy or powdery substance. This is a sign of long-term and extensive freeze-thaw damage that has completely broken down the concrete’s structural integrity.

Does a frost heave damaged wall always need replacing?