4 Reasons to Get a Soil Study in the Brazos Valley

One of the first questions I ask when I get a request for a foundation design is – "do you have a geotechnical report?" People unfamiliar with the soils in the Brazos Valley usually respond – "do I need that?"

YES YOU DO.

Below are four (4) reasons why you need a site-specific geotechnical report before starting a foundation design:

1.      To find out if you have expansive soils

Expansive soil is prevalent in the Brazos Valley, Houston, and in the DFW area. These clay soils act like a sponge – during the dry season, they lose moisture, and during the rainy season, they gain moisture. This loss and gain can make the surface clays swell and shrink by about 6 inches on average in the Brazos Valley and Houston, and as much as 12 inches in the DFW region.

Without proper building pad prep and a stiff foundation, your building will be going on a seasonal ride. And it will be uneven. This ride will show up in the form of cracks in your building façade – especially if you have brick or stucco. There will also be cracks in the interior drywall, and your doors will stick as the years go by. Buildings that do not have a proper foundation in this region typically need expensive foundation repair work done after construction.

2.      To figure out what kind of foundation you need for your building

One should never guess on how to design a foundation in this region because of these expansive soils and the havoc they can wreak on your façade. The most important thing about the geotechnical report is that it comes with foundation suggestions and design information. The geotechnical report tells you whether you can have a shallow foundation with grade beams and a slab, or whether you need piers. If piers are needed, the report will indicate the proper layer to bear the piers, and what their capacity should be. This design information is crucial for the structural engineer to properly size your foundation.

3.      To figure out how to prepare your building pad

One way to use a shallow foundation on a site with expansive soils is to remove and replace the clay with a non-expansive structural fill. A lot of people assume to take the top 2 feet off, but this varies even in the Brazos Valley, with as much as 6 feet needing to be removed and replaced around the Anderson area. In the DFW region, it is not unheard of to remove and replace up to 12 feet of soil. The remove-and-replace depth is not something you want to guess at – the geotechnical report will indicate how much to remove based on soil tests for your specific site. The report also provides guidelines on how to install the new fill by providing information on how much moisture the new fill must have at the time of installation, and how to properly compact the fill to avoid uneven settlement.

4.      To figure out if you have a high water table

A high water table with groundwater near the surface can impact the type of foundation you need for your building, and more importantly, the cost of building such a foundation. If you can use a shallow foundation, the impact of groundwater might result in the use of pumps and trenching to facilitate construction. If you are dealing with piers, the impact of groundwater might result in using steel casing during construction. Both of these solutions can add significant costs to your foundation construction.

In summary, a geotechnical report has a lot of crucial information that your structural engineer needs to design your foundation - ranging from what type of soil you have, what type of foundation you need, how to prepare your building pad, and if there are special situations that will influence construction methods and costs.

Need help on a project? Call 713-909-0458 or email info@o3structural.com