San Antonio Geology & Your Pier & Beam Foundation

san antonio geology river bed

A major metropolitan area in Texas, the 7th most populated city in the United States, San Antonio is home to about 1.5 million residents. These many residents are spread across a 465 square mile area of South Texas, accompanying tens of thousands of commercial buildings and residential homes with a vast geological landscape. The integrity of these buildings relies heavily on the success of topsoil support and adequate drainage, a feat achieved by proactive management and ownership.

This post is intended to highlight the varying types of geology across San Antonio and the foundation challenges property owners must face, particularly owners with the classic pier and beam foundation build. Read on to learn more.

Geological Formations of San Antonio

Bexar county spans three main geological formations; so, the surface geology of San Antonio and its surrounding metro consists primarily of Cretaceous (Gulf), Cretaceous (Comanche), and Eocene rock variations. Two of the rock formations in this county are comprised of a limestone-shale sequence. This is often referred to as “layer cake geology,” which produces clay-rich soils with very shallow soil horizons.

Accompanying those rock variations, complementing the development, are a wide variety of soil types as well as streams that have cut through canyons and revealed the geological development over millions of years. In fact, Texas is home to over 3,700 rivers and streams. Between these water sources and inconsistent rainfall, it can be difficult to keep up with the measures required for structural maintenance in San Antonio.

Pier & Beam Foundations in San Antonio

This brings us to the next point, and the primary foundation type we’re focusing on for this post: pier and beam foundations (sometimes called pier and post foundations).

Older than the more contemporary method, the concrete slab style, pier and beam foundations rely primarily on stacked blocks, concrete piers, or steel piers for building weight support. These piers are accompanied by beam and joist assemblies running perpendicular over the piers as well as an above floorboard installment.

Is It Safe to Have a Pier & Beam Foundation in San Antonio?

Absolutely. Pier and beam method may be a bit dated, but that doesn’t mean it’s worn out its uses or presents any significant hazards for modern living. Slab foundations have simply taken over the mantel for new builds for their cheap and efficient design. That said, there are a few things to note, especially as it relates to the land surrounding your home or commercial property, which we’ll get into next.

3 Ways Land Affects Pier Foundations

While there are many potential influences, both natural and unnatural, to a pier and beam foundation’s integrity, we’ve narrowed down these three ways that land may naturally impact your structure in a pier and beam setup.

#1 Shrink-and-Swell Soil

Texas is home to a plethora of soil typesMuch of this soil is what’s known as expansive soil. When left unchecked, expansive soils will go through a potentially damaging expanding and shrinking process. Hence the term “shrink-and-swell soil.” When this occurs, a few things can happen: 

  • First, expansive soils can put pressure on a building, causing cracks in concrete and wood. While this is especially important for slab foundation owners, expansive soils can still affect pier and beam foundations as well. 
  • Another potential danger to your pier and beam foundation is when the expansive soil shrinks back down and leaves behind grooves in clay, causing inadequate water drainage that may lead to flooding.

What Causes Soil Shrink and Swell?

Inconsistent rainfall (which San Antonio experiences year-to-year) and large tree root systems are primary culprits of shrink-and-swell soil in this area. Roots that are too close to your home greedily absorb the moisture and minerals that soils need to remain at a healthy balance.

In other words, expansive soils that shrink and swell are dependent on the amount of water the land absorbs. This leads us to the next point.

#2 Topsoil & Erosion

Your piers rely on the support of healthy topsoil to maintain their strength. When the topsoil erodes from weather or becomes weakened by a lack of adequate moisture, your foundation can be compromised and it may even lose years off its originally anticipated lifespan. This is one of many reasons it’s vital to have a proper landscaping and drainage system in place.

#3 Geology & Natural Water Accumulation 

Speaking of landscaping and drainage – San Antonio geology and the natural accumulation of water around your home go hand in hand. While the suspension of a pier and beam foundation gives it an advantage over other foundation types—at least as it relates to water accumulation—it’s never good to have land with pooling or even flooding water surrounding your building. Excess water can cause the deterioration of materials like wood and it can cause concrete (you may have concrete piers) to break down more easily. 

Every yard is different. The formation of your land may be beautiful, but if you don’t adjust your landscaping accordingly, you may have issues down the road. 

San Antonio Pier & Beam Foundation Repair

We also offer our services throughout Texas, including Austin, Dallas-Fort Worth, and Houston communities. 

Give us a call or email us for more information on San Antonio foundations. You can also schedule a no-charge evaluation with our experienced Texas foundation repair company. 

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