Understanding Bedrock and Load-Bearing Strata

Whether you’re building a simple family home, a huge building, or a megastructure, choosing the right foundation is essential. The foundation does two things; it distributes the weight from the walls to the underlying bedrock and keeps out groundwater and moisture. 

Geology, topography, soil composition, building type, and building size will determine the kind of foundation that’s right for your structure. Here, we’ll explain what load-bearing strata are and when it’s necessary to create a deep foundation. 

Foundations are designed to transmit the structural load they support to the underlying soil. But what happens if the soil below is shifty or likely to suffer compression? 

What Is Load-Bearing Strata? 

Load bearing strata refers to the underlying soil or rock that can bear the weight of a building or structure without shifting or compressing. These soils don’t settle or sink too. They are regarded as “non-active” meaning they are inert and won’t experience expansion or contraction like the silty sand or clay soil directly below the foundation. 

When Is It Necessary? 

Deep foundations are necessary when a building or structure is erected on sand or other soft soil that can’t absorb the structural load. Such soil can’t ensure structural integrity. So, a foundation is created deep underground on load-bearing strata that go 20-65 feet below the ground. At such depth, builders can establish contact with the stronger rock layers on the earth. 

Types of Deep Foundations 

Deep foundations are used to support larger structures. However, they can also support the weight of homes built on steep inclines, on the beach, over water, and in other unique areas. As the name suggests, they’re built deep into the earth. Let’s look at some sub-types. 

End-Bearing Piles: When the soil on which you built can’t bear the building’s weight, the builders have to bypass the soft soil layer to get to the bedrock below to distribute the load safely. Sturdy columns are driven into the ground until they come into contact with the rock layer. This allows the weight to be transferred via piling into the rock. 

Friction Piles: Crafted from concrete or H-shaped steel, they facilitate the exchange of forces with the soil surrounding the column, taking advantage of its surface area. The amount of load a friction pile can support is proportional to its length. Each pile has an area of influence and has to be spaced evenly to ensure proper distribution and absorption of weight. 

Caisson Foundations: While they’re commonly used to construct bridges and piers over water, they can also support freeway overpasses and hillside buildings. Caissons can be floated to the drilling site or prefabricated. 

What’s the Right Type of Foundation? 

Well, this depends on the building size, location, and geotechnical issues you’re facing on-site. The decision to build a deep foundation or a shallow one also depends on the type of soil underneath. Before you start construction, ensure the soil can support the foundation and preserve the structural integrity of your building. 

If your floors are sinking or uneven, the foundation is likely built on a weak or unstable foundation. The experts at JES Foundation Repair will examine your foundation and recommend an underpinning solution to strengthen the foundation and bring back the floor to its original position. 

We offer a variety of piering solutions including helical piers, push piers, and slab piers. Slab piers are specifically used on structures with a slab foundation, helical piers are ideal for lighter structures, and push piers that are most commonly used are best for heavier structures. 

The Piering Process 

The exact piering process may look different depending on the type of piers used, but the installation of push piers typically looks like this: 

The footing is first notched out and prepared so the bracket attaches to the house firmly and the piers sit under the foundation wall. Next, the bracket is inserted and the external sleeve driven to the ground using protractors. This ensures piers are straight when they go down. 

Push piers are then hydraulically driven through the soil one at a time using the weight of the building and the surrounding soil as a counterweight until they reach bedrock or other load-bearing strata. 

Once resistance is reached, all piers are load-tested to identify a consistent pier depth and appropriate load-bearing strata. Engineers and contractors use a simple math equation to correlate capacity to hydraulic pressure while factoring soil conditions on-site, the building’s weight, and prevailing environmental factors. 

After each pier has been driven down, hydraulic lifts are attached in a sequence to allow the building to be lifted simultaneously. Applying pressure to the piers at the same time means less pressure is used to lift the structure than to drive down the individual piers. 

The home is then lifted off the active soils and the weight of the home is transferred onto the piers and in turn, onto the load-bearing strata. 

If you have a foundation that is experiencing settlement and needs a deep foundation solution like piering, contact the expert team at JES Foundation repair for a free foundation repair inspection and quote today.