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Last updated April 3, 2026.
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There are a specific set of items to include in a foundation investigation in order to achieve the most accurate conclusions. In this series, I am covering these 16  items in detail over the course of several posts. Below I will cover soil conditions and why they are an important factor. 

Soil Conditions are Top Priority in Items to Include in a Foundation Investigation 

Most foundation problems boil down to how they are supported by the soil. So the first item to include in any foundation investigation is assessing the known conditions of the soils. The more sources you use to assess the conditions the better, and there are several sources to consider. Of course, it is best to sample the soils directly and analyze them in an ASHTO (The American Association of State Highway and Transportation Officials) certified lab. However, sometimes in the name of keeping costs in line this may exceed what the market will bear. 

Observation of the Onsite Conditions Should Not Be Overlooked

The on site investigator should look around and observe what they see. Some of these observations should include the following. 

• Are there sidewalks on site that show signs of heaving? Theoretically sidewalks and concrete paving can settle, however due to the large area and low comparative weight, heaving is more likely than settlement. 50 lbs per sf of 4” thick sidewalk is not much weight considering most soils support 30 times that weight.  

• Are the soils exhibiting signs of clay shrinkage?  Are there signs of desiccation (shrinkage cracks)? To test for clay I like to get a sample of the soil from a few feet below the surface. Then I will add water and roll it into a cigar shape. If it rolls up without falling apart, then it is clay. Of course this can only be used in the case of near surface soils.

Be Aware of Various Sources, Methods and Scenarios 

One of the primary sources of information is the National Soil Conservation Resource survey. This is a fairly accurate, yet general map of known soil conditions. It usually gives information on a specific depth, usually the top 5 feet from the surface. A sample pic is below. 

Bear in mind that this is not the end all be all source on soil condition information. For example, in one particular area, there may be tremendous soil problems, yet it reads as having low expansion potential on the map. This can happen because the original clays in the soil were deeper than 5 feet.

This is why several sources and methods are necessary. It is also why soil conditions are only one of the items to include in a foundation investigation.

 In the above scenario, much of the upper soils were removed during development, leaving the unburdened, expansive clays near the surface. This can lead to the soil heaving more easily.  Additionally, on this same NCRS site, more precise data is available by putting in more precise locators. Even so, it is still generalized and limited.

Look Beyond the Immediate Location for More Data

If there are existing soil reports on the specific site, they usually contain fairly accurate information. Yet it should be noted that in most scenarios, that information is not available. In that case, sometimes reports from nearby sites can be useful, bearing in mind their distance from the site and the variability of the geologic conditions in the area.

Of course, being familiar with the geologic history of the area and its variability can inform further investigation. Historical aerial photography can also greatly help. 

Once you understand the soil layer compositions, you can use this information to understand important factors such as:

• If the site has the potential for heave or settlement. 
• The likelihood of the mechanisms of soil movement given sources of water and their proximity to depositional layers.

All the Items to Include in a Foundation Investigation Require Interpreting Data 

Collecting and interpreting all this data then helps interpret additional observational data, providing context for possible characterizations of that observational data. Data should be interpreted and all factors considered in this way throughout every step of the process. Gathering data without interpreting it defeats the purpose of collecting it. Keep this in mind as you learn about all 16 items to include in a foundation investigation and the processes involved. 

Next up in the list of items to include in a foundation investigation: Water. Without changes in moisture within the soil, changes are not very likely.