A sinking foundation refers to a foundation that settles or sinks into the ground, such as a sinking concrete slab. This is often caused by unstable soils, leading to structural issues like cracked concrete, misaligned windows, and leaning chimneys. Meanwhile, a collapsed foundation is more extreme. This refers to a severe structural failure where the foundation has fully deteriorated and no longer has the ability to support the rest of the property. To fix either situation, contact foundation contractors for assistance.