While sandy soils remain stable as water passes through them, soils rich in clay undergo significant changes based on their moisture content.
When clay type soils dry out, they shrink significantly — so much that the ground can become covered with cracks. But after a heavy rain, the cracks are gone and the soil is fully saturated with water.
Because clay soil absorbs so much water, it expands during wet weather. Expansive clay soils can put enormous pressure on your basement or foundation walls. When the pressure becomes more than the wall can handle, the wall will begin to push inwards.