Frost heave is a phenomenon where soil swells upward due to the formation of ice during freezing conditions. When the temperature drops below freezing, the moisture in the soil turns into ice, causing the soil to expand and move upward. This movement is caused by the continuous supply of moisture through capillary action, which results in the growth of the ice mass.
Sometimes, the weight of the soil can restrain the influence of the ice, leading to the formation of ice lenses. However, these lenses can still cause the soil layer to move upward. Frost heave can cause significant damage to various structures such as roads, channels, and foundations, ultimately affecting the superstructure.
To prevent the detrimental effects of frost heave, it is crucial to understand the underlying mechanisms and identify the key factors that contribute to its occurrence. Once these factors are identified, appropriate measures can be implemented to prevent frost heave from causing damage.
How It Works?
As temperatures drop and freeze, the moisture in the soil also freezes, turning into ice. This freezing process causes water from other parts of the soil to move towards the frozen area through capillary action. As a result, the ice mass in the freezing area increases in size. However, the weight of the soil and other objects above it restricts the growth of the ice mass, leading to the formation of ice lenses.
Fig. 1: Ice lenses and Capillary Rise of Water
As freezing temperatures persist in the soil, they can create ice lenses that form within the ground. These ice lenses continue to grow towards the surface as the temperature drops further. As the ice lenses expand, they exert pressure on the surrounding soil, thrusting the soil layer upward. This upward force can result in cracks in the soil and cause damage to foundations, which can ultimately affect the stability of the superstructure. It is worth noting that when moisture in the soil freezes and transforms into ice, its volume increases by approximately 9%. This expansion further contributes to the formation and growth of ice lenses in the soil, exacerbating the potential for damage to structures built on or near frozen ground.
Fig. 2: How Frost Heave Works
Frost heave action is facilitated by three main factors: fine grain frost-susceptible soil, continuous moisture supply to ice lenses, and freezing temperatures. As the temperature drops, the water in the soil freezes, forming ice lenses that push the soil particles apart and cause the ground to heave upwards. When the temperature rises again and the ice melts, the soil structure settles back down under its own weight. However, the repeated cycles of freezing and thawing can severely deteriorate and potentially collapse the soil structure, posing risks to infrastructure and stability of the ground.
Effects
During the freezing season, channels are susceptible to destruction, which can cause a range of issues. One major problem is a decline in the load carrying capacity of the subgrade, which can lead to sinking and instability. Additionally, the pavement can experience undulations and considerable damages, making it unsafe for drivers and pedestrians. The damage caused by freezing temperatures can even extend to the foundations and slabs, causing further structural issues. As such, it is important to take precautions to protect infrastructure during the winter months, such as reinforcing channels and regularly inspecting and maintaining pavement and foundations.
Prevention
Frost heave can be a major problem in areas where temperatures drop below freezing. This phenomenon occurs when the moisture in the soil freezes, causing it to expand and push upwards. In order to prevent frost heave, it is important to eliminate one of its basic elements, which include fine grain soil, frost temperature, and water.
Fortunately, there are several measures that can be taken to avoid frost heave. One option is to provide frost heave prevention systems, such as a hydronic heating system. Another solution is to extend the foundation, such as piers, below the frost line.
Additionally, providing backfill materials, such as gravel, around the foundation can encourage water drainage and prevent frost heave. It is also important to use a sleeve to avoid ice from gripping the concrete and to construct a footing that can withstand upward movement.
For road construction, replacing fine grain frost susceptible soil with coarse granular soil is a viable option to prevent frost heave. The use of a capillary breaker can also prevent the movement of water toward the freezing front, which can reduce the influence of frost heave.
Stabilizing the soil is another measure that can be taken to prevent frost heave. Finally, protecting the concrete from frost by using various protective measures can also be effective in avoiding frost heave. Overall, there are many methods available to prevent frost heave and mitigate its negative effects.
