Simply stated, settlement is the movement your home experiences when the soil below can no longer support its weight. Maybe you're thinking, "My home used to be structurally sound. What changed?!" The simple answer is that the soil changed. Your home is resting on many different layers of soil. Each layer has different properties, such as, soil type and moisture content. How compact or loose each layer is also varies because, these layers formed over time, starting with the Earth's original formation. Some layers were carried and deposited by water, some by wind, and some by glaciers.
Companies that develop land for building and home construction may have even placed layers of fill soil over the soil created or deposited by Mother Nature. Land is commonly cut down or filled to produce relatively flat, buildable homesites.
Typically, soil layers get more compact and stronger with depth. In most locations, the native top layer is the newest and least compacted soil. That makes it easier for plants and other vegetation to grow.
Below the earth's crust, you'll find layer after layer of soils that are composed of a mixture of clay, silt, and gravel. The exact mixture varies greatly by location and how they were deposited in the first place.
Deep below those layers is a layer of bedrock, or load-bearing strata. A basic knowledge of soil and bedrock layer and their properties is important as we explore what causes foundation settlement, and most of all, what works and what doesn't to fix it permanently.