This information is from HIE Consulting Engineers
UNDERSTANDING COLORADO’S UNIQUE EXPANSIVE SOIL
Nov 16, 2017
As of 2016, Colorado was the second-fastest-growing state in the nation, adding just over 100,000 residents between 2014 and 2015, according to estimates from the U.S. Census Bureau. Since 2010, the state has grown by more than 408,000 residents. That puts us in the top four nationwide in terms of population growth in the last seven years, behind only North Dakota, Washington D.C. and Texas since 2010.
Whatever the percentage, the fact is a lot of new residents have been moving to Colorado, particularly the Front Range, and this trend doesn’t look to be slowing down anytime soon. They’re coming for the weather, the economic growth and the lifestyle—even the local craft beer scene is attracting new Coloradans.
But what many of these people don’t know is that Colorado is home to a specific type of risk that can and will damage their new homes if not properly addressed.
The soil in Colorado is very dry and, as a result, expands and contracts based on moisture content. This type of expansive soil can be very dangerous to structures, shifting and cracking foundations as it shrinks and then breaking into walls as it expands when water is added to it. It’s like the freeze-thaw cycle, only with the added pressure of tons of dirt and mud, and it can wreak havoc on improperly framed basements and homes.
Most of the Front Range and the Eastern Plains are underlain with soils that are expansive, including most of Logan, Morgan and Washington Counties in the northeast corner of the state where more than half of the soils have high swelling potential. Only the eastern portion of El Paso County, east of Colorado Springs, even falls in the moderate category, with less than half of its soils showing moderate swelling potential. The rest of the Front Range is average or above.
Expansive soil can be found in all 50 U.S. states and, according to the American Society of Civil Engineers, as many as 25% of U.S. homes are at risk. In fact, expansive soils cause more financial losses for insurance companies in a typical year than all natural disasters combined.
The term refers to soils that contain water-absorbing minerals, such as certain clays, that expand as they absorb water. Although all soils contain minerals, it’s those with a high-concentration of expansive minerals like smectite, bentonite, montmorillonite, beidellite, vermiculite, attapulgite, nontronite, illite and chlorite that are particularly at risk. Expansive soils are also known as “expandable soils,” “expansive clays,” “shrink-swell soils” and “heavable soils.”
Not surprisingly, when the ground under and around a structure gets wet and starts moving—and some expansive soils can expand and shrink by more than 10% depending on the water content—significant forces are exerted on the structure itself. This can cause damage ranging from foundation shifting, basement wall and floor cracking and other problems, including damage to above-ground structures related to these foundation movements.
In addition to swelling when water is added, these expansive minerals also shrink as they dry out, which can cause ground cracking and foundation pull-back, which removes needed structural supports and can cause further shifting. Fissures, or cracks in the ground itself, can also form in dry expansive soils, allowing moisture to penetrate deeper underground, causing further structural damage and exacerbating the shrink-expand cycle.
IDENTIFYING THE PROBLEM
For homeowners on Colorado’s Front Range, it’s a safe bet that the ground underneath their homes is at least somewhat expansive. As mentioned, conditions range from moderate to significant across most of the eastern half of the state, but everywhere there is at least a chance of soil-related damage. It is only a question of how much risk you face.