Different Soils and How They Affect Foundations in Construction

When it comes to construction and any type of building project, the ability to know the type of soil to use goes a long way in determining the outcome of your project.

Some soil types are perfect for any type of construction while others are not as good. Hence, you need to be wary of this when planning your foundation in order not to have a building with a very weak foundation.

Using the wrong type of soil for your foundation or construction can be very disastrous. It could lead to your foundation becoming weak, cause the building to sink, develop fissures or, worse of all, make the building collapse.

This is why the importance of having the right soil for your construction cannot be overemphasized.

 

Features of a Good Soil for Construction

The following are some of the features that make a soil ideal for your construction project:

• It must have stability during wet and dry seasons
• It must have good structure and physical properties that can give room for stability during the construction process
• Good soil must have balanced chemistry to be able to withstand any type of building that’s being constructed on it
• The soil must be able to capture precipitation so that it can withstand erosion and runoff

To determine the above features in the soil, you need to get a soil map. This is accessible through some soil scientists or the USDA Natural Resource Conservation Service at the Web Soil Survey website.

 

Importance of Having a Soil Map

• The chemical, physical, and biological properties of the soil are given in the soil map
• It gives room for accurate implementation of sustainable land management and usage
• The soil map suggests the potential for water runoff, drainage, or storage
• It can be used to determine the slope of the surface of your land

 

Types of Soil Foundation Techniques

Since various types of soil differ in properties, engineers now determine the foundation technique to be applied based on the soil's characteristics and the load of the structure to be built on it.

Hence, the foundation of a building helps to greatly determine the structural wholesomeness of that building.

The two major types of foundations are shallow foundations and deep foundations. 

 

Shallow Foundations

This is called "shallow" because its depth is low. The foundation is wider than its depth and is commonly used for lightweight structures. The various types of shallow foundations are:

 

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• Isolated Spread Footing

This foundation technique is used when the soil has a high bearing capacity even at a shallow depth. For instance, loam soil.

 

• Combined Footing

Oftentimes, the deep foundation technique is applied when building on soil with low bearing capacity. But combined footing is a good choice too if the structure is lightweight. 

 

• Raft or Mat Footing

This is used when the soil is loose, weak, has a low bearing capacity, and requires the load to be spread out.

 

• Wall Footing or Strip Footing

This strengthens individual foundations and prevents their horizontal distortion during construction.

 

Deep Foundations

Deep foundations are required when the soil on a piece of land is sandy soil or soft soil, and when it cannot withstand the load of the building that's being constructed.

The soil has to be dug deep to provide adequate anchor or firmness for the building to be constructed. The following are the various types of deep foundations:

 

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• Pier foundation

It is a good choice when a multistory building is to be constructed. It is often used when rocks are to be placed beneath the foundation or when the soil beneath the foundation is stiff clay.

 

• Caisson Foundation

This technique is used for buildings constructed below water bodies, especially when a dam, pier, or bridge is to be constructed. It has several types including box caissons, pneumatic caissons, excavated caissons, floating caissons, sheeted caissons, and open caissons.

The construction engineer is saddled with the responsibility of choosing the type that best fits the building to be constructed.

 

• Pile Foundation

This is an ideal choice when the soil of the foundation to be constructed cannot carry the weight of a large building. The ground is dug deep to increase the bearing capacity of the soil.

 

Types of Soil and Their Effects on Foundations

1. Clay Soil

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Clay soil is usually found where streams and rivers once flowed or in an area where water tends to sit after heavy rainfall. Clay is composed of fine mineral materials and little organic materials.

It is often sticky when wet and does not drain well. It is not an ideal soil to use when building a foundation because it is not stable.

When wet, it expands and pushes against the foundation's wall due to its tiny particles. And when it dries out, it shrinks and causes the foundation to shift. It can lead to fissures and unequal floors in a building if used without amendments.

To build a foundation on clay soil, the ground has to be dug deeper to increase its stability. The appropriate type of foundation technique for clay soil is a drilled pier or a slab-on-grade foundation technique.

A slab-on-grade foundation regulates the soil's tendency to expand and shrink after construction while a drilled pier foundation increases its structural firmness or stability if dug deeper. 

 

2. Peat Soil

Peat or organic soil is found in the wetlands. It is dark brown or black and has a distinctive smell, a low-bulk density, and consists of decaying or organic matter.

Although some crops can grow well on it, it is wet and acidic and not usually the best choice for agricultural purposes.

Peat soil can absorb a large amount of water and can become extremely dry during the dry season. It also has a high carbon content and is similar to dry wood when dry.  This makes it highly flammable; the fire is very difficult to put out when it begins to burn.

The unstable nature of peat soil makes it one of the worst soil to build a structure or foundation on. This is because any building built on it is at risk of developing cracks or other types of damage in the future.

 

3. Silty Soil

This type of soil can be found near the river, lake, and other water bodies. It is made up of rock and other mineral materials.

Silt soil is a very smooth and fine soil when felt with the hands. It also contains small particles and can hold water for a long period. When likened to sandy soil, it has much smaller particles; hence, moving currents can easily transport it.

It is very fertile and can be used for agricultural purposes. However, it is not a good soil to build a foundation because it puts the building under stress. Silt does not dry out quickly or easily when it holds water.

It, therefore, drains poorly and expands to press against the foundation. This makes it very weak support for construction.

 

4. Loam Soil

This is the best soil for building foundations. Loam soil is also called agriculture soil because it is the best soil for planting. This is why it is found in areas where farming is very successful.

It is the best and richest soil for planting crops because it contains sand, silt, clay, humus, and can retain moisture and nutrients. It also has a higher calcium and pH level when compared to other types of soil.

It is the ideal soil to build a foundation due to its sand, silt, and clay constituents, which are the right combination for construction.

Loam soil handles moisture appropriately as it absorbs moisture and dries out at an even rate. It also allows for air circulation and drains nicely. However, it should be filtered of undecomposed particles or materials before placing a structure on it. This is to avoid future disastrous consequences.

 

5. Rock or Bedrock

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Rock is the right choice to use for the construction of larger buildings like skyscrapers, duplex, and multistory buildings; this is because of its high bearing capacity. Rocks offer a limited risk of the formation of cracks or fissures in a building because they have a high bearing capacity.

Rocks include granite, hard chalk, limestone, shale, and sandstone. They have great stability and depth. You can place your structure on any rock of your choice but ensure that they are well leveled before building the structure.

Bedrock is a layer of rock that is beneath a soil surface. It is made up of igneous, sedimentary, or metamorphic rock. It is stable and can resist water damage. This makes it a good choice for construction.

 

6. Sand and Gravel

Sandy soil is formed from the breakdown of certain rocks like granite, quartz, and limestone. It is low in nutrients and cannot hold water. This makes it a bad choice for agricultural purposes.

As for building foundations, sand and gravel are suitable because they have large particles, which aid the quick drainage of water. This means that there is less risk of putting a building under stress.

Stress in a building can lead to the formation of both structural and non-structural fissures that could eventually lead to the collapse of the building. For better stability or support, sand and gravel can be compacted with other good soil types like loam soil.

A lasting foundation technique for this soil type is screw piles or helical plier. It prevents the sand from washing away and also holds the foundation firmly.

 

Conclusion

Soil types vary in physical and chemical properties; they also have their unique importance during construction. Whether you plan to use a particular soil for agriculture or construction, you need to check the type of soil in your location or construction site before using it.