When it is rainy, the ground gets saturated and expands. When it dries out, the soil shrinks. The result is inevitable settlement.
Settlement is the movement your home experiences when the soil below can no longer support the weight of your home. So what changes over time making this happen? The soil does. Heavy rains and dry periods are independently causes of settlement.
During heavy rains and flood conditions, the soil holds on to the water and becomes very soft. This soft soil can be weak, causing the home to shift or sink down into it. In some ways, it is similar to when you step in mud and your foot squishes into the soil. As a side note, if poor drainage is allowing water to stand or pond near your home, the soil will absorb the water and again, weaken the soil.
So what happens when we have a dry period without rain? The soil begins to dry out. And when soil dries, it shrinks. As the amount of soil around your house shrinks in size, it creates an empty space for your home to settle into.
Dry spells are one cause, but maturing trees can cause problems as well. The root system of a tree is often two times the size of the tree canopy. This means, a tree with branches that extend over your home most likely has roots that extend under your home. Yes, this can cause issues on it's own, but, those roots also draw out moisture from the soil. When the soil starts to dry out.. well... we've already talked about that!
Because we are dealing with Mother Nature, the constant cycle of wet and dry periods means that settlement of a home is never over. The ONLY way to know settlement is "done" is to FIX the problem.
The fix will be different from property to property depending on the foundation type, but the theory behind the approach remains the same to permanently stabilize.
View a commercial that shows a simple demonstration of water expanding soil: https://youtu.be/v1wIybMye7c
Excerpts taken from our book, Foundation Repair Science, written by Dave Thrasher, Amanda Harrington, and Larry Janesky