This may be caused by seasonal high water tables or underground springs and seeps. If your home is in the flood plain of a nearby stream or creek, it may be affected during periods of heavy rainfall. If the house was built in the path of a natural drainageway or a site that is lower than the surrounding area, you could also be affected. Normally, a footing drain pipe is laid along the base of the foundation to channel ground water away. Too little moisture, especially during dry periods, can cause the soil to shrink and the foundation to settle.
Some plants remove water from foundation soil, causing a drying effect.
Helping the soil maintain a consistent moisture level, by watering properly, is extremely beneficial. Consult a foundation specialist on the best type of method, usually soaker or subsurface weep hoses. Excessive moisture in expansive clay soil can cause it to swell and heave the foundation. Proper grading and drainage can greatly minimize any soil expansion, especially if the moisture level is adequate to begin with. Other causes of excessive moisture are plumbing leaks beneath the foundation.