In a word: moisture.
It seems ironic that water would cause a problem in a state that’s sometimes called the Great American Desert.
But among the rock and granite common to Arizona, you will find clay, a soil that is susceptible to expanding when it gets wet.
Too much water can cause the soil to swell. Excess water can get into the soil under and around a home during a heavy monsoon rainstorm, if your home has a plumbing leak or if water isn’t draining away from your home properly because it sits at the bottom of a slope.
Conversely, too little water causes the soil to shrink.
If the soil under your foundation were to swell or shrink uniformly, you probably wouldn’t have a problem. But if the soil shrinks or swells under only part of the foundation, it can push that part up higher than the rest (this is called “heaving”) or cause it to sink lower than the rest (called “settling”).
Either way, your foundation will move and crack. That can throw your house out of alignment, a problem that, at its worst, can cause thousands of dollars of damage to your walls and roof.
The problem gets worse with every Arizona drought. In addition, subdivisions built on irrigated agricultural land are having problems. And the pumping of groundwater to make way for new neighborhoods is drying out the soil in those areas and causing settlement and heaving problems for the people who move into the new homes.
In fact, too much groundwater pumping over the years, especially in Pinal and Maricopa counties, has caused problems not only for house foundations but for roads.
Fissures form when excessive groundwater pumping lowers the water table. The settling of underground sediment can cause the ground to sink unevenly and open opening surface cracks, called fissures. When it rains, the cracks sometimes expand to a gaping size, allowing them to suck parts of highways and foundations into the earth.
