Concrete can sink or settle for several reasons. If the original concrete was installed on dirt that had not been compacted properly, the slab will start to settle within a few years. Soil erosion is another big contributor and is fairly common in some parts of the United States. The earth also naturally settles over time so if the slab is over seven to ten years old, it may be the natural progression of things. In any case, once the concrete does start to tilt or sink, it can cause walking hazards, unwanted water runoff, or major foundation issues.
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