The primary cause of foundation movement is the shrinking and swelling of expansive clay soils as such soils alternately dehydrate and hydrate. As expansive soils absorb water and swell, they typically exert upward forces measured in thousands of pounds per square foot. The lifting forces exerted by expanding soils can easily lift light residential structures such as homes.
The weight of a residential structure varies widely from point to point. For a pier and beam home with a wood substructure, the middle of a room can weigh as little as five pounds per square foot. For slab foundations, open portions of rooms can weigh as little as 50 pounds per square foot. The heaviest parts of a typical home are the exterior walls. In a two-story home, with brick veneer, and three-foot-deep perimeter grade beams, along the edge of a foundation typical loads are in the range of 2,000 pound per square foot. Even for the heaviest parts of a home, the pressure of expanding soils can easily lift the foundation and the overlying structure.
By definition, expansive soils swell as they absorb water and shrink as they dry. Any factors that change the water content of the soils under buildings can cause foundation movement.
The most common factors are:
- Seasonal changes in rainfall
- Drainage, or the lack of drainage
- Plumbing leaks
In addition, foundations can move when the underlying soils compact and decrease in volume or when soils move downhill. Downhill movement is referred to as soil creep if the movement proceeds slowly, or as slumping if the movement proceeds more rapidly.
Occasionally, foundations are moved by other factors, such as soil rebound, erosion or washouts, trees, and dissolution.
Why Advanced: At Advanced we understand why and how foundations move. For each home, based on the available information, we make the recommendation that we feel best fits the situation. We offer steel pilings, cable anchored steel pilings, concrete pilings, drilled piers, drainage correction, lowerings, tunnels, chemical injection, and other services. Call 214-333-0003 or fill out our form to request a free estimate.