On the ‘small’ matter of foundation settlement

Last Updated 9 months ago by Kenya Engineer

Have you ever thought of why:

1. carpenters fix doors and windows nicely and after some time, the doors will go out of position, making it difficult to open and close them?

2. You align windows properly and after some time, you’ve to forcefully open and close them?

3. Why there are cracks in your walls?

In this article, we explain to you why all these happen.

When you build, your house exerts so much pressure on the land beneath it, causing Soils under the foundation structures to deform. When this happens, your building goes through a process called foundation settlement. For easy understanding, let’s say (Sinking). Buildings suffer damages due to settlement of its foundation specifically when the settlement occurs in a quick manner.

There are two forms of foundation settlement
1. Uniform Foundation Settlement
2. Differential Foundation Settlement

Uniform foundation settlement is when the settlement (sinking) occurs at nearly the same rate throughout all portions of the building. Uniform settlement has minimal detrimental influence on the building unless it becomes pronounced.

Differential foundation settlement is when settlement occurs unevenly, and to different portions of the building at different times. It causes one side of the house to sink, unlike uniform settlement where the entire house sinks unanimously. And this is where the problem is.

Differential settlement can distort the frame of the building, floors may slope, walls and glass may crack, and doors and windows may not work properly. You’ll also notice cracks on your floors, drywall cracks, foundation cracks and deterioration of slabs.

Now you understand why your doors can’t open and close freely even though your carpenter fixed them very well ?

What causes foundation settlement?
1. Incorrect sizing of foundation: If your foundation is not properly designed, you’re likely to encounter differential settlement.

2. Expansive Clay: the properties of your land can easily cause your foundation to sink. Clay for instance, expands when soaked with water. As such, it will cause an upward movement of your foundation, and when the water content is low, it causes the foundation to dip.

3. Poorly Compacted Soil: Many people after setting up their foundation do not allow the filling to settle. They rush the project and cast the floor overnight. Well, you’re not doing yourself any good. Be getting ready for foundation settlement. When all your tiles start falling apart, don’t blame your tiler.

4. Trees and vegetation: I’m sure you’ve heard it many times that it’s not good to keep trees closer to your house. The reason behind this is what I’ve explained to you. If there are trees closer to your house, their roots could lift the foundations and damage them.
Therefore, special attention should be made if you want to plant trees around your home.

we delve deeper into SOIL COMPACTION and see how it can cause foundation settlement.

Soil compaction simply means compressing the soil used to fill your foundation to create a denser layer (rock-like) platform for the building to sit on. It occurs when soil particles are pressed together to reduce the air space between them.  The common term used is “FILLING.” The act of pouring sand into the foundation to create a smooth surface for oversite concrete/ floor casting.

The purpose of soil compaction is so the soil can support the building. If there’s anything you want, it’s solid ground that can carry the load of your building.

Soil compaction is a little like pregnancy, whether you conceal it or not, it’ll manifest. Many people after filling their foundation, rush to do oversite concrete without ensuring proper soil compaction. If you don’t compact the soil, what will happen is that, a hollow layer will be created between the soil and the building, and this will cause foundation settlement. That’s the reason behind cracks in walls, tiles removal, titled doors and windows, making it difficult to freely open and close, cracked slabs etc.

We can demonstrate this by fetching sand of equal volumes into two separate containers. When you press down the sand in container A, you’ll observe the level will decrease. If you want the container full, you’ll have to top up with more sand. You’ll repeat this process until the container can’t take anymore sand. The soil becomes dense and hard. This is the point where you can say the soil is properly compacted, and can hold the weight of the structure.

However, in the second container, you’ll equally observe that the container is full. Nonetheless, if you put any item of significant weight into it, you’ll notice the object will sink.

The essence is that, the soil in container B isn’t compacted; it has a lot of air and pores in them, making it less dense, and more prone to foundation settlement. Water can easily pass through it, and you know what will happen. You don’t want water to compromise anything under your home and cause damage.

This is the same story with building on poorly compacted soil. The whole point is to make the soils dense so water doesn’t break in or navigate through and cause erosion.

How do I ensure proper soil compaction?
1. If you’re not in a hurry to complete your project, then leave your foundation to settle by itself. When you do the filling, allow time to pass, and let rain and sun do the magic. Do you realize that when you fill your foundation to the brim, and it rains over time, the filling drops, and you’ll have to top up again and again? Yes! That’s the natural way of ensuring proper compaction.

2. If you’re in a hurry to complete the project, there are compaction machines available. Hire one and use it. The practice where your mason lifts blocks and drops them hard on the filling won’t achieve any desired results.