What Causes Expansive Soil?

Expansive soil is a kind of soil as opposed to a condition that can be caused in soil. Expansive soils are those which are made of certain kinds of earth. Of course, some conditions are required to cause expansion and contraction and certain conditions can exacerbate these processes and put extra strain on your property. 

• Clay and Peat 

Expansive soils are those which are primarily made up of moisture-retaining materials like clay and peat. Clay-based soils are undoubtedly the most expansive soils. This is because of the huge capacity of clay to absorb water and the slow rate at which it drains and dries out; when clay is dehydrated, it contracts and can crack. When it is wet, however, it can increase in size by up to a third. 

Peat-based soils, too, retain water very well and expand when they are saturated. However, they expand with slightly less force than clay and have a slightly higher tendency of becoming marshy. This means that while peat-based soils can expand and cause bowing walls, there is also a chance that they will cause subsidence. 

• Climate and Weather 

Certain areas of the U.S. are more likely to see bowing walls and cracked foundations as a result of the higher proportion of expansive earth in the soils. However, clay-based and peat-based soils can be found all over the country. Those properties that are most harshly affected by expansive soils tend to be those that are also placed in changeable climates. 

Repeated changes in temperature and soil saturation are hugely important to the likelihood that expansive soils will cause damage to a home. This is partly because of how the moisture in soil reacts to temperature (for example freezing). Mostly, however, it is because of the likelihood of fluctuations between severe saturation and dehydration.