Cut and fill is a major problem due to the expansive clay soils in the Dallas and Fort Worth areas of North Texas.
Why does improper fill cause a foundation problem?
Clay soil that has not been properly compacted will consolidate over time.. and we are talking about decades. As the soil consolidates, it drops, and the foundation above it is no longer properly supported. A foundation that is not properly supported will fail as it too will drop.
What is required to achieve a proper fill?
To properly “fill” a building site, the expansive clay soil must be compacted in no more than 4 inch layers, and be at the proper moisture level during compaction. Proper moisture means that the clay soil can neither be too wet or too dry.
Why can a site cut cause a foundation problem?
When a site is cut down to a uniform height, expansive clay soil that was covered with over burden is now exposed to the water. Newly cut soil can be characterized as dry and compact. The compacted soil is good, but as the expansive clay hydrates (gains moisture), it will expand. If a foundation is built over a newly cut area, it may heave as the soil hydrates.
Cut and Fill is the worst case scenario for a foundation.
For all the reasons explained above, a foundation straddling a cut and fill is a disaster waiting to happen. The foundation tends to heave in the cut area, while sagging in the fill area.