A critical part of understanding how a foundation may react to collapsible or expansive soil is discovering how water interacts on the site. This matters for both present and past conditions equally. A great tool for understanding these interactions is using aerial photography in site inspections. 

What Using Current Aerial Photography in Site Inspections Can Show Us

Current aerial photography shows how water interacts on the site presently. This is illustrated in the diagram below. Take note that grassy areas are typically overwatered by landscapers in order to keep the grass green. This overwatering has a tendency to cause the excess water to flow through the soil, only to find its way under a foundation. 

Other potential drainage issues could be caused by where the water drains to, based on the slope of the trusses. This is especially true if the trusses drain into small side yards that are not sloped well enough for draining the water that reaches them. This is often the scenario.

These Photos Help Us Come to Conclusions When Analyzed  

Of course, outside of using aerial photography in site inspections, it is super important to identify onsite issues such as existing gutters and hard pipe drains.

Seeing a backyard pool can indicate a probable drainage problem too. Why? Because almost every pool has Deco drains. These drains catch the water that spills out of the pool. However, they typically do not lead to any kind of a discharge area, and sometimes, they are cracked. Therefore, it simply soaks in, injecting water into the soil at its location. This water then finds its way under the foundation.

You may notice trees on the property when using aerial photography in site inspections. While the previously mentioned issues can cause water to oversaturate the onsite soil, trees can indicate moisture suction from the surrounding soil. The closer to the house and the bigger the tree, the more impact it will have. Some trees, depending on the species, will draw more water than other species. Although, once in a while, you may see a sharp peak that happens near a large tree, in the profile at the edge of a foundation and floor slab. This is usually indicative of root disturbance from the tree itself. Meaning, the root growth lifted the foundation and floor slab. I have seen mere eight inch roots do tremendous damage.

Take Note of Construction Details When Using Aerial Photography in Site Inspections 

Examining aerial photography in site inspections also shows the location of the load bearing ends of the trusses are, as opposed to the gable ends. And these have considerably less weight on the footings. From this you can deduce that the areas with more weight could be more susceptible to settlement, and less susceptible to heave. This is why every detail that affects soil should be analyzed during a site inspection.

 Examine Past Site Details with Historical Aerial Photos 

While current aerial photos expose what is currently happening on a site, historical aerial photos can tell you about the history of the site before the home was built. This is important because the site’s past use can have hidden effects on the current build site. You can learn, for example, if it was farmed, and if so, to what was the extent. Case in point, I remember one house that had been built over the old farmer owner’s animal burial pit.

By using historical aerial photography in site inspections, you may also learn about arroyos or drainage paths that existed in the past. Therefore, clues are given about the depositional material, its relative density and residual moisture contents.

 Using Aerial Photography in Site Inspections Exposes Many Potential Issues

Aerial photography is just one of the  important tools that are a part of our arsenal. These tools help us understand foundation performance in conjunction with the other data. For example, when seeing a high area near grass we might assume that moisture is being injected, causing the heave. But that’s only true if there are clays in the soil. 

Conversely, seeing a low area near a tree might also suggest that the tree is pulling moisture from the expansive clays and shrinking them. Because this can cause settlement. However, if the soils are non-cohesive and non-expansive, then the additional moisture could induce settlement. It is by combining the data from our use of aerial photography in site inspections with other available data that we can start to build a clearer picture. We can, with collective data, learn about the performance of the foundation: heave vs settlement, potential long term performance, and any possible remediation measures needed. 

This is why using all the tools at our disposal is critical. Weighing all the factors, while analyzing all the data will equal the best outcomes. Aerial photography is just one of the tools available to us.