While we might understand that the Earth as a whole is moving around in space or that the tectonic plates that our Earth is made from are slowly moving, we don’t normally think about the fact that soil is also moving with gravity. So, how long does it take for soil to settle?
It takes anywhere from a few months to 7 years for soil to settle, depending on the soil’s composition. “Settling” is the process of the soil compacting upon itself due to gravity over time.
Understanding the process of soil settling is critical to ensure that any construction projects are done correctly. Read on to learn more about soil settling, including how long it takes different types of soil to settle, how to speed up the process of soil settling, and why soil settling is important.
Soil Settling in Different Types of Soil
Imagine pouring a pile of rocks on the ground and a pile of plain dirt onto a patch of pavement. When the two substances fall through the air, they land at the same time.
When you step on the pile of dirt, you might feel it sink beneath you slightly. Meanwhile, when you step on the pile of rocks, you won’t sink. This analogy explains, in simple terms, how different types of soil will take different amounts of time to settle.
Let’s take a deeper look at the four major types of soil:
- Peat-Based Soil
- Clay or Silt-Based Soil
- Loam-Based Soil
- Sand or Gravel-Based Soil
Peat, created from organic materials that have been compacted together, can settle very quickly. If wet, peat can settle within only 5 or 6 months, making it the fastest settling soil.
However, if peat is dried out, it will not settle. In fact, if peat becomes too dry, it becomes so light that it can be picked up by the wind and blown away.
Clay or Silt-Based Soil
Clay and silt tend to settle relatively quickly compared to other types of soil. Clay and silt normally settle entirely within 1 or 2 years but can settle quicker depending on the conditions they’re exposed to.
This is largely due to the makeup of clay and silt. Clay and silt, at a microscopic level, are just groups of small groups of particles (similar to sand). This means that as these particles weigh toward one another, they quickly compress.
Loam-based soil is a combination of clay, silt, and sand. Similar to clay or silt-based soil, it is made from a number of small particles that weigh down upon each other.
However, the sand in loam is much heavier than clay or silt. This actually makes it so that the sand pulls the entire combination of dirt particles down while the clay and silt try to hold the sand in place. In most cases, loam takes about 7 years to settle.
Sand or Gravel-Based Soil
Soil is ultimately settled when the friction of the particles acting upon each other is so strong that the substance is able to fight gravity enough to remain in one place. Sand and gravel generally don’t apply much friction to one another, making it so that it takes a long time for the soil to settle.
Sand or gravel-based soil normally takes about 7 years to settle, but the process can take longer.
Factors That Cause Soil to Settle
While soil settlement is a process that will occur due to gravity over time, there are also some other factors that might cause your soil to settle faster. These are not actions that you should take intentionally to change the pace of soil settlement, but they do sometimes occur outside of your control.
Rain Pushes Soil Downward
When water falls out of the air during rain, it can reach speeds of about 22 miles per hour (35 kilometers per hour). Thus, when raindrops hit the ground, coming to a complete stop in a matter of milliseconds, the impact of the water hitting the soil is very hard.
When this occurs over and over again through the years, the impact of the rain can cause the soil to settle at a faster rate than it might normally.
Freezing and Thawing Cycles Cause Soil Movement
If you live in an area that gets very cold in winter, you’re probably familiar with frost heaves on the road. These are caused by the soil moving up and down as it expands and contracts due to the moisture in the soil freezing.
This process occurs in all soils, leading to the soil moving and compressing over time. This means that, no matter how often you till your soil, the freeze and thaw cycles will always increase soil settlement.
Wheel Traffic Applies Impact to Soil
Imagine stepping into the sand on a beach. When you step, your foot compresses the sand, and you “sink” slightly. Though less noticeable in regular soil, the same process occurs every time you step.
More importantly, this process occurs at a much stronger degree when you use a motorized vehicle or have other tire traffic on a soil plot. Over time, the wheels will push the soil down and will make it settle at a much faster rate than the surrounding soil.
Changing the Pace of Soil Settlement
Understanding that soil is composed of different types of material that settle at different rates, it is easiest to change the rate of soil settlement by adding or subtracting different components to the soil to speed up or slow down the process. However, there are some ways in which you can impact the rate of soil settlement.
Let’s take a look at three ways to change the rate of soil settlement.
Use Water to Speed up the Process
Using water is not only an effective way to speed up the rate of soil settlement but is also a necessary factor for soil to settle in many cases.
As you pour water over the soil, the water seeps into the pores of the dirt between particles. The dirt (which is denser than water) then sinks to the bottom of the water droplet, compressing on particles below it. As this process repeats itself, it can cause the time for soil settlement to decrease drastically.
Install Vertical Drains So Soil Settles Faster
Another technique you can use to make your soil settle quicker is using vertical drains to allow added moisture to drain quickly from the ground.
While just the sheer act of using water can increase the rate of soil settlement, it also creates an issue in the fact that the excess water takes longer to drain through the ground into an aquifer. Using a vertical drain can alleviate this issue, making the soil settle quicker.
Prevent Fast Settlement by Introducing Roots
While ensuring that the ground is settled fully is important, there are also some instances in which you might not want the soil to settle as quickly. One way to prevent this settlement is by adding plants, which introduce roots to the soil. Similar to how plants can prevent soil erosion, they can also work to help slow down the rate at which your soil settles.
Soil Compaction Affects Gardening
After understanding how long it takes for different types of soil to settle, as well as how you can change the rate of soil settlement, you might be wondering how soil settlement can impact everyday life.
Understanding soil settlement is important for those interested in gardening. Plants require water and oxygen in order to survive. If the soil they are planted in is not oxygenated enough and too compact, your plant might not be able to grow. It is important that soil is not allowed to settle completely.
Soil settlement is an incredibly important topic both within the context of gardening and construction. Depending on the type of soil, soil can settle between a few months and several years. If you want your soil to settle quicker or slower, try using water or vegetation to impact the time it takes to settle.