What causes foundation failure? What makes foundations weaken and lead to cracks in walls and floors, doors and windows that won’t open, stairs that come away from the front porch and chimneys that separate from the house?
There are six main causes for foundation failure, poor construction is only one of them. Four of the top causes for foundation failure are soil related.
Here are the top six main causes for foundation failure.
1. Soil type, especially expansive clay soil
2. Poorly compacted fill material
3. Slope failure, mass wasting
5. Poor construction, and
Let’s explain each of these six causes.
1. Soil Type – Expansive Clay Soil
The most common kind of expansive clay can absorb so much water that it can swell by several hundred percent. The pressure from this degree of swelling can easily life most residential homes. There’s also an electro-magnetic component that further contributes to the swelling. The technical term for when this expansion pushes foundations upward is “heave”. gunite
Not only do the soils expand with moisture, they also contract with dessication, causing up and down movements known as differential settlement. Foundation underpinning is essential to preserve structural integrity.
2. Poorly Compacted Fill Material
If the fill material on a lot is not sufficiently compacted to support the weight of the structure above it, there will be foundation problems. The problem can be from the mix of odd fill materials, and from poorly compacted fill, or a combination of both. So if you’re choosing a lot to build on, and get to see it before it is built, confirming the fill material and the degree of compact could give you important information for your peace of mind.
3. Slope Failure / Mass Wasting
Geologists use the term “mass wasting” to describe the movement of earth downhill. It could be “creep” which is slow, or “landslides” which are sudden. Slope failure as we use it refers to “creep”.
While underpinnings can act as a barrier to “creep”, the power of gravity is such that unless the underpinnings were specifically designed to stop slope failure, warranties can’t usually cover underpinnings in sites exposed to slope failure.
Erosion may be the most straightforward cause of settlement issues. It can come from poor drainage, uncontrolled water flow or lack of ground cover. If not identified early, erosion can wear away the soil around foundations, creating a new need for underpinning.