When building a basement, it is important to check the soil type of the construction site. After all, stable soil is needed to create a strong foundation. If you choose clay, there are precautions you should take to avoid damage. That's why we have researched how clay soil affects basement construction.
Clay is not the best soil for building a basement, but you can still build your basement on clay soil. However, it is a must to do the necessary soil preparation to avoid structural damage in the future. Contractors should do a lime treatment on the soil to stabilize it and control ground swelling.
Clay soil holds moisture, so it can cause the basement to sink or rise depending on moisture levels. The placement of the foundation should also adhere to the movements of the ground. Hence, it would be tricky to use clay. Keep reading to learn how you can build your basement on clay soil.
Is Clay Soil Hard To Build On?
Yes, clay soil is hard to build on. It isn't easy to build on clay soil because of its characteristics. If you use clay for construction, it may not be strong enough to support the basement.
The water-holding capacity of clay is the main problem. As the seasons change, the soil shrinks if it gets too saturated with water and rises if it goes dry.
The effects of using clay soil include the following:
- The expansion of soil transfers the pressure to your home's foundation. As a result, you would notice the bowing and cracking of the foundation walls. When there are cracks, your basement is at risk of water seepage.
- When the soil contracts, there could be a big gap between the foundation and the backfill. If it rains or floods, the water might settle along the base of the foundation. Thus, it would also be a problem as soon as the soil expands again.
- With the water deposits near the foundation, it would find its way under the concrete slabs. In effect, your basement would be prone to problems like mold and structural damage.
Read further on how you can mitigate the effects of clay soil when building your basement.
How To Prepare Clay Soil For Construction
Contractors will stabilize the soil by doing a lime treatment before adding the foundation. The procedure is vital to make the ground compacted. Clay soil's load-bearing capacity can improve, as lime stabilizes the soil.
Here are the steps how to stabilize clay soil with lime:
- Dig out several inches of soil around the perimeter of the basement foundation to create trenches.
- Create a mixture of lime with 20 to 60 percent of water. You can use crushed limestone, quick lime, or hydrated lime.
- You will need around 24 to 48 hours of mellowing period. During this time, the contractor remixes the soil and makes it ready for compaction.
What Type Of Foundation(s) Is/Are Suitable For Clay Soil?
To find a suitable foundation for clay soil, you must know the various conditions present. By doing so, you can select the right materials and processes involved in setting up the foundation.
There are two subtypes of clay soil. Each type will have different processes and limitations. Read below about these types and the factors to consider.
1. Uniform Firm And Stiff Clay
Uniform firm clay is a well-grade soil, having almost the same granular sizes that form large masses. Stiff clay has low plasticity, which means it has more strength to bind with other soil particles. Both stiff and uniform clay have more bearing capacity than soft clay.
Here are three scenarios you should be familiar with before you select the foundation for your basement:
- First, for areas without vegetation, you can choose among these foundation types:
- Raft or floating slab
2. If existing trees are surrounding the location, the suggested foundations are the following:
- Concrete piles that support reinforced concrete ground beams and precast flooring
- Concrete piles carrying an unmoved concrete slab
- Trench fills based on the location of trees, hedges, or shrubs
- Raft foundation
3. Lastly, if there are trees but you plan to cut them down, you can choose among these foundations:
- Reinforced concrete pile
2. Soft Clay
Soft clay has a low bearing capacity with high compressibility. This type of soil will include soft silty or sandy clay and soft silty sand. It would not be easy to build the basement with soft clay. That is why it is essential to choose a suitable foundation type. Listed below are some choices:
- Pile (to a compacted layer below)
- Wide strip footing
- Pier and beam
Adding the foundation is not a DIY project. You might cause more issues if you proceed without supervision and thorough planning. It is also good to prepare a budget to get high-quality and durable materials for the foundation.
Can You Pour Concrete On Clay?
If you plan to pour concrete on clay, it can be very challenging. Clay tends to compress under the concrete's weight. As a result, your slab will sink over time. The moisture from clay could also seep through the concrete, causing a brittle base and irregular curing.
Prevent the issues with proper preparation and execution before pouring concrete. Here are some tips you can follow:
- Level the area where you want to pour concrete.
- For very soft clay, make the base for your slab firmer by excavating and mixing gravel with the soil.
- You can add a layer of 2 to 4 inches of gravel to create a barrier between the slab and soil.
- Add a 3/8- or 1/2-inch rebar inside the frame to support the concrete slab.
- Compress the soil with a soil tamper or plate compactor. The more that you compress the soil, the more weight it can bear.
Although it would seem tiresome, the extra processes will help maintain your basement's structure.
What Is The Best Soil To Build A House On?
The soil on which you build could make or break the foundation of your home. Searching for a residential lot with the best soil type can be tough. The varying locations, environment, and weather conditions may not live up to your expectations.
Good soil must have the following characteristics:
- Stable during wet (expansion) and dry (contraction) cycles
- Retains water and precipitation well (to prevent runoff and erosion)
- Includes minimal organic material
- Has more rock and compacted sand or gravel
- Balanced chemistry to prohibit corrosion with the infrastructure
Based on the list, loam and rock are the best types of soil for house construction. Learn why you should find these types of soil in the area you want to build your house.
1. Loam Soil
The composition of loam soil is a mixture of clay, sand, and silt. This type has balanced properties that are great for supporting foundations. Also, make sure that there are no organic or assorted soils mixed with loam. Some types of soil could allow water on the surface.
2. Rock Soil
With high load-bearing capacity, rock soil is a strong choice of soil for residential construction. You can choose among bedrock, hard chalk, limestone, sandstone, or shale. The rock soil should be at a level with the foundation to get the right support.
If your lot has clay soil, you can still build your basement with the right foundation.
Clay soil is tough to work on when you plan to build a basement. With the weak properties of clay, it may not be ideal to choose this type of soil for construction. You will need extra time and effort to prevent structural damage in your basement.
But you can still work with clay as long as you do the necessary ground stabilization and preparation. It is also vital to select a suitable foundation based on the current conditions of the soil.
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