Greatest Destroyer of Structures? Soil

Hello Science Enthuists,

id you know that Soil is the greatest destroyer of Houses and Buildings in the United States. Have you ever seen a crack in the walls of your house or a building and thought it was because of earthquakes and tornadoes? Well, the cause of it is from nothing but from Soil. Yes, Soil causes more damage in the US than Earthquakes, Floods, Tornadoes, and Hurricanes combines! This phenomenon is called Expansive Soil.

Different Types of Soils in the US

 Expansive Soil

Expansive soil is when the soil (most expansive soil is clay) change their volume depending on the moisture content of the Clay. Clay swells when there is more water and shrinks when there is less water. Even though this might be a small change, it can cause a lot of damage to the building on it. This is a small mechanism where the size, shape, and arrangement of the changes based on the amount of water the soil is being exposed to. This kind of soil is not avoidable since large portions of the US Gulf Coast and Great Plains have their types of soils. In these places, large cities like Houston, San Antonio, and Dallas are located in this type of soil. If someone wants to build a house or a building in these places, the expansive soil in their areas is something to consider since it breaks things. 

Movement

Movement on its own including basic movement doesn't cause a lot of damage because of all of the damage but the real cause of damage to a building or a house is Differential movement. There are 2 types of movement: Uniform and Differential Movement. Uniform Movement is when an object moves uniformly. All the parts of the object move the same amount.  Differential Movement is when all the parts or all the sides are not moved the same. This is also known as Uniform Settlement and Differential Settlement. The image below will give you a better example of Uniform and Differential Settlement.

 

This is the reason we can move large structures like houses from one place to another. Differential Movement is caused by Expansive Soil. This is because when the soil expands or contracts, it does not do so evenly. For Example: If a house sits on a concrete slab, and you have not seen rain for a long time, the moisture in the top and edges of the slab might dry off and in response, the soil in the edges might shrink while the interior remains relatively wet. Now, the slab that the house is sitting on does not have support in the edges. Because of this, Differential Settlement occurs which causes cracks all along with the affected places of the wall.

Expansive soil doesn't only cause damage to houses and buildings, it can also cause issues like sinkholes caused by broken pipes underground and creaks in the roadway also caused by soil expanding. Swell Pressure is the pressure exerted by clay when there more or less water present in the clay. What engineers have to find is how to counteract the swell pressure and how to make a structure that can withstand the swell pressure of Clay soil. A little 10% increase from its normal state is enough to make a huge crack in the wall which can be up to 6 - 8 inches long!

Ways the Mitigate Expansive Soil

There are 4 ways to Mitigate Expansive Soil:

1. Remove the expansive soil- One way to Mitigate expansive soil is to just remove the expansive soil and replace it with soil with lower swell pressure. This is very effective but you have a bunch of expansive soil after the project.
2. Grading the soil around the building or house- Grading the soil around so that water can drain away from the structure is also a really good solution but a problem with this is that the building will be higher than the rest of the area and can require a lot of space.
3. Mixing Chemicals into the soil- Mixing chemicals into the soil so that the swell pressure is a really good idea and is often used most of the time since it doesn't require anything more and can be very helpful. But a downside to this method is that it ruined the ecosystem and environment of the area and the chemicals can be harmful to the birds and animals living in the habitat.
4. Building higher- This is used because building higher counteracts with the swell pressure, therefore, minimizing the damage done by the soil but this is harder than other methods because the soil is very strong and you will need a lot of weight to counteract the swell pressure of clay soil. This method, in most cases, is just not feasible. 

The simplest way is to not build in expansive soil places at all but this idea or method is not an option in most cases because, like I said before, a lot of major cities (At least in the US) are located in these types of soils. Houston is the biggest and even the 4th biggest city in the US! So, not building in these soils is not a valid method. 

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Sources and Citations:

• Grady. “How Soil Destroyed Buildings.” Google Search, Google, 25 Oct. 2017, www.google.com/search?q=uniform%2Band%2Bdifferential%2Bmovement&safe=strict&rlz=1C1GCEA_enUS812US812&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjMocSzv-7eAhUEmeAKHUKOCgMQ_AUIDigB&biw=1366&bih=626#imgrc=TYFV4F4817KQ7M:
• Friedman, Daniel. “Detect, Diagnose, Evaluate & Repair Foundation Movement Buckles, Bulges, Bows, Cracks, Creep, Impact, Leaning or Settlement Damage.” What Is Electricity? Electrical Definitions: Definition of Amps, Definition of Volts, Definition of Watts, Daniel J. Friedman at InspectApedia.com, inspectapedia.com/structure/Foundation_Movement_Types.php.