In this series of blog posts, we will explore common soil myths related to the foundation repair industry and their implications for real estate. Here is a partial list of some of those myths. I wish to uncover in more detail the following blogs:
Top Soil Myths in the Foundation Repair Industry
- Dirt is dirt…Many think it’s not that complicated.
- All cracks in a home indicate that foundation repair is needed.
- All foundation repair is about fixing settlement.
- Homeowners insurance covers foundation repairs.
- Foundation repair salespeople are “qualified design specialists.“
- The free analysis by foundation repair contractors is a bargain.
- Permits pulled by the contractor ensure proper engineering.
- All engineers are qualified.
- Lifetime warranties give assurance.
- The state licensing boards overseeing contractors will protect homeowners from problematic foundation repair contractors.
- Foundation repair salespeople are under oversight to ensure the protection of homeowners.
- You can successfully sue foundation repair companies for improper designs and bad diagnoses.
- Over time, foundations stop moving. Or if the foundation is moving, it will continue to move.
- City and county inspectors will ensure proper construction of foundation repairs.
- Once the work begins, city/county inspectors help protect homeowners from unfair change orders.
Myth #1: Dirt is dirt. Soil is not that complicated….. hardly.
Layering
So, let’s start with the first soil myth I’ve identified: the soil is a big colored mass of homogenous contiguous soil.
Nothing could be further from the truth. Soil is deposited in layers. Each of those layers has different thicknesses, mineral deposits, densities, and affinities for water. Water moves through these layers, interacting with them in complex ways. The layering isn’t always perfectly horizontal; instead, it can slope, thicken, or thin out, creating an intricate underground landscape. See the illustration below.
Types of Soils
The types of soils that are commonly encountered are:
- Clays
- Sands
- Silts
- Gravel
There are many different mineral types for each of them. Sand, silts, and gravel are easier to understand behaviorally.
When these soils are deposited, they may not compact adequately to support the weight above them. When wet, they can consolidate, squeezing out air and causing any loads on top to sink.
Clay Soil and its Unique Characteristics
One important type of soil to highlight is clay soil, particularly expansive clay. There are various mineral types of clay, with Montmorillonite and Kaolinite being two common expansive varieties.
Clay particles are extremely small—so small, in fact, that the only way to see them individually is with a scanning tunneling microscope. These clay particles carry a slight negative charge, while water has a slight positive charge. This ionic charge interaction occurs because of the balance between electrons and protons. As a result, water is attracted to clay and, when given the opportunity, can position itself between individual clay particles.
When a water particle is deposited between these tiny clay particles, they tend to expand away from each other. This phenomenon leads to my favorite saying: “Clay sucks.”
Engineers call this process negative pore pressure, which occurs when water contacts very dry clay. The water wicks through the clay, moving towards the driest areas, thereby causing the clay to expand.
Because clay is so dense, water does not move through it quickly, which is why it’s often used for lake liners to prevent leaks. However, as I mentioned earlier, soil layers are deposited horizontally, allowing water to travel easily between these layers.
If one of these layers is clay, it can become saturated horizontally, reaching a considerable distance to a more porous layer, such as sand or silt. When the clay comes into contact with this larger area, it expands.
The easiest way for clay to expand is upwards because it is typically constrained on both sides and below. When this upward movement occurs, it can exert significant pressure, potentially breaking concrete or bending steel in the structures above it.
The Ramifications to the Foundation Repair Industry
It is crucial to understand this concept, as it is often misunderstood within the foundation repair industry, particularly by contractors and their salespeople. This lack of understanding can lead to significant misdiagnoses. For example, when heaving soils cause one part of a slab or foundation to rise higher than other areas, it is frequently misinterpreted. Instead of recognizing that the elevated portion has heaved, the issue is often seen as the lower portion settling, even though it has not moved at all.
However, clay can be a double-edged sword. When it dries out, it shrinks, which can create additional challenges for foundations.
This is evident in photographs of clay soil that show numerous cracks. When clay becomes very dry, it shrinks, creating these fissures. However, when wet, those cracks close up.
This contrasting behavior demonstrates the cyclical nature of clay as it swells and shrinks. In regions with alternating wet and dry seasons, the soil can experience continuous upward and downward movements, depending on moisture levels over time.
How Soils Can Interact Together
So now you get an idea of how complex soil can be. Depending on drainage, sun exposure, tree roots (which suck out the water from the soil), and many other factors, different parts of a property could be experiencing different behaviors. And if there is a mix of clays and silts and sand layering, there could be opposite behaviors even if drainage, tree roots, etc, are the same in an area.
Why Geotechnical Engineers are Needed
The signs of stress caused by both heaving and settling can often appear very similar. Indicators such as wall cracks, misaligned doors and windows, cracks in the floor, and sloping floors can all signal foundation issues and are often only interpreted as settlements.
This is why it is vital to have a thorough analysis conducted by a qualified geotechnical engineer. I will delve deeper into this topic, as well as the remaining soil myths in a future blog.
I think that one factor about the soil laying below structures, which is ignored, is the cut and fill. In the cut, upper layers have been removed, which may fully or partially include the clay layer. In the fill, there is a mix of soils. Houses built on a slope may have different movement under different sections.
For sure! the cut and fill complicate the picture even more.
The current IRC actually has written sections that the building official SHALL determine areas of expansive, compressible or other unknown characteristics. In lieu of a soil investigation, they will allow using the lowest strength in Table R401. Which is 1,500 psf bearing capacity. The soils estimated with that bearing capacity are the worst in our area. Louisiana.
Code further says you can remove treat and or stabilize the soil. How do you
know what to do without a soil investigation.
Further says that if the soil has 4 characteristics (you have to perform a soil investigation to determine this characterisics. But if the plasticity index PI is greater than 15, the foundation MUST be engineered according to the IBC not the IRC.
IBC says foundations on expansive soil must be engineered according to WRI/CRSI or PTI codes. Wire Reinforcing Institute, Concrete Reinforcing Institute or Post-Tension Institute. All of these slabs are a waffled grid pattern slab designed for the expansive soil.
Brian interesting comments. currently repair pile products are currently installed under the IRC with their ICC es reports allowing a FOS of 2.5 instead of 2 when there is no soil information. the requirement of reverting to IBC for soils with PI greater than 15 would seem to contradict that or perhaps overrule. As you point out how would you know if the PI is greater than 15 without testing? perhaps the original report for the development?