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Bedrock and Load-Bearing Strata

Bedrock is a geologic formation that gives a sinking foundation a second lease of life.

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Your home’s foundation is crucial for the safety and well-being of your household. If it’s sinking under the weight of your home, you will have to dig deeper and underpin it. Foundation repair experts generally recommend the installation of a deep foundation system over the bedrock to stabilize your home.  

What Is Bedrock? 

Bedrock refers to any mass of rock that is solid and tightly bound. It lies several feet below the ground and can contain large stones and other larger solid materials. Because the bedrock is dense, it can bear significant weight without shifting or compressing.  

As such, it typically isn’t affected by weather or moisture changes that cause the soil to expand and contract. However, in areas of high erosion, bedrock may become exposed to the surface. Surface exposure of bedrock is known as an outcrop.  

Types of Bedrock 

Knowing what type of bedrock lies under the ground is an integral part of building a house. Builders can use this information to help create a strong support for the type of house you want to build.  

Generally, bedrock formation falls into these three groups: 

  • Igneous bedrock: When molten lava or magma cools and solidifies within the earth, it will form igneous rock.
  • Metamorphic bedrock: This type forms when existing rocks change their form due to exposure to heat, pressure, and reactive fluids like hot mineral-laden water over a long period of time.
  • Sedimentary bedrock: Over time, minerals that settle out of the water, air, or precipitation can solidify. Such minerals accumulate in layers to form sedimentary rocks, which are porous and softer than igneous and metamorphic bedrock.  

The Depth of Bedrock 

There are several ways to measure the depth of bedrock. This includes digging, drilling, desk studies, and other geophysical methods. Since the depth of the bedrock varies from location to location, it’s important to know what types of foundations can support your home.  

Shallow foundations: When the load imposed by a structure is lower than the bearing capacity of surface soils, builders can erect a shallow foundation. 

Raft foundations: This is a slab that covers a wide area, often the entire footprint of a building. This type of foundation is suitable for ground with poor conditions. The foundation floats on the ground like a raft. 

Deep foundations: If the surface soils aren’t compact or strong enough to bear your home’s weight, the most sensible thing to do is to install piers. These systems transfer the heavy weight to deeper layers with a greater bearing capacity.  

Bedrock and Foundation Settlement 

The best way to repair settling foundations is to support them with foundation piers. Your contractor will drive steel piers into the ground until they reach the bedrock, which can bear the weight of your home without crumbling. Once the piers reach the bedrock, they will meet resistance. It’s this resistance that will help your contractor permanently stabilize and potentially lift your foundation back to its original level. 

You have the choice of either stabilizing your home at its current position or lifting it back to a higher elevation. Like with any foundation repair solution, it is crucial to consult with an expert to determine which type of foundation works best for your case. 

Can You Build Directly on Bedrock? 

Yes and no. You can build on top of the bedrock if it comes near the surface, but that’s not a common scenario. To get to the bedrock, you will have to excavate tons of surface soil. This is costly and unnecessary. 

When the soil beneath your house can no longer support your home’s weight, the structure may start to settle into the ground. The resulting foundation settlement can lead to severe and costly structural damage. For more information on how you can stabilize your foundation, contact Tar Heel Basement Systems and schedule a free foundation inspection and repair quote today.

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