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Underpinning illustration

What Is Underpinning?

Underpinning is one of the methods of fixing settling or shifting foundations.

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Changes in soil composition do affect the foundation of many buildings and structures. The culprit is often shrinking or weak soil. Because they’re shifty, the foundation has to be reinforced. Otherwise, it will settle, crack, or crumble. This isn’t good for a building’s structural integrity. 

Let’s look at what is underpinning and the different types of underpinning products in the foundation repair industry. 

underpinning methods

What Is Underpinning? 

Underpinning is the process of bolstering and supporting the foundation of a building, house, or structure. It entails reinforcing the existing foundation and strengthening the underlying soil by extending the foundation so that the load above is evenly distributed over a larger surface. 

The underpinning process begins by excavating and removing the soil directly under the foundation. Soils are removed in stages to minimize the risk of undermining the foundation, which can lead to structural problems. The depth of excavation is determined by a structural engineer, who examines the soil and identifies the strata that’s suitable to hold the load. 

Once the soil is replaced with the underpinning material, the process is repeated in the next section of the foundation until the entire structural base is reinforced. 

Importance of Underpinning 

Homeowners underpin their homes or structures for various reasons. Some do so when the existing foundation isn’t strong enough to bear the load of the structure or their house has changed in some way. Others use underpinning after realizing soil properties were not factored during building design and construction. 

In some cases, underpinning is done after the purpose of a building or structure changes following a major renovation. It’s also done whenever a new construction nearby requires excavation of the soil that holds the existing foundation. 

Underpinning also helps enhance the capability of a foundation, especially when the property owner wants to add another story. 

It’s also necessary to underpin a building after an earthquake or drought as these conditions can make the structure unstable. 

Types of Underpinning 

When reinforcing the foundation, contractors use the following methods. Let’s look at what each entails. 

Pile method: It’s commonly used by foundation repair contractors. In this method, foundation piers or piles are installed evenly along the foundation to lift it and transfer the weight of the unsteady concrete to the stable bedrock. It’s immensely useful in fixing foundations built on expansive or soggy soils. 

Pit method: The foundation is divided into sections, holes are drilled on the foundation wall, and a supporting needle with a bearing is attached to hold the foundation. A pit is excavated and a new foundation is created beneath it. 

Mass pouring: It’s used in situations that require shallow underpinning, not deep excavations. The weak underlying soil is dug out and concrete poured in its place to strengthen the foundation. 

Temporary Underpinning 

If your foundation problem isn’t severe, foundation experts can underpin the structure of the home with either of these solutions: 

Concrete Underpinning: Soil around the foundation is dug out and huge concrete footings are poured under the existing footings. Once the concrete dries up, the soil is backfilled. What this does is extend the footing. However, it won’t stop the foundation from shifting. 

Concrete Piers: These are short and precast concrete cylinders that are driven into the soil. They go on top of each other and are secured with a wire. Shims are then placed right on top of the uppermost cylinder and the soil is backfilled. The downside to this method is there’s nothing to guide the pillars. As a result, they don’t go deep into the soil. 

Durable Underpinning Solutions 

These methods are permanent underpinning solutions that address foundation settlement: 

Push Piers: The most commonly used type of piers for stabilizing and potentially lifting a settling foundation back to level. These galvanized steel push piers are driven to bedrock and load-bearing strata to better support the weight of the home. 

Helical Piers: Helical piers serve the same purpose as push piers and are screwed down mechanically into the earth till they reach stable soil. These systems are best used to support the foundation of lighter structures like chimneys and patios. 

Slab Piers: Contractors use slab piers to support and strengthen concrete slab foundations. The piers are driven deep into the stable soil, securing your home and lifting the slab and interior walls back up. 

If your foundation is crumbling due to weak soils or any other issue, contact JES Foundation repair and request a free assessment. We’ll determine the problem and install the appropriate underpinning solution.

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