Foundation slippage is a common type of foundation damage found in homes built on sloping sites. With this type of damage, a foundation element (wall, footing, slab, or pillar) can begin to move downhill in response to gravitational forces, ground pressure, and other factors. Since foundation elements are usually joined with a combination of reinforcing steel, continuous masonry, or framing; multiple elements can be affected when one element changes.
If left unaddressed, foundation slippage is likely to get worse over time. Homeowners occupying sloped sites are encouraged to contact a foundation repair specialist if they notice foundation damage. When proper repairs are done in a timely manner, high repair costs and more dangerous damage to foundations can be avoided.
Sloping sites present problems
Contractors prefer to build a home on a flat, open site, but they don’t always get away with it. Sloped sites are often developed because flat sites are no longer available. They can also be chosen because of the attractive views and other features like rock outcroppings to create a special appeal. Regardless of the reason for developing a sloped site, homeowners have reason to be concerned when landslides cause foundation damage.
A number of forces and factors are usually involved when soil creep occurs. The most obvious is that the gravitational force causes the ground pressure to increase as the slope becomes steeper. Vegetation often helps stabilize a steep slope, because plant roots cement the soil and also help absorb excess moisture. However, vegetation also adds weight to the soil. You can increase the downward pressure on a base if most of the roots are above the slip plane where ground movement is most likely to occur.
A discussion about the movement of soil usually involves water. The stability of the soil is enhanced by a certain moisture content, in the same way that wet sand can be molded into a solid shape. However, adding more water to a sand sculpture will cause it to crumble and wash away. Soil can behave in a similar way. On a sloping site, the pull of gravity begins to affect the soil when a certain level of moisture saturation is reached.
Foundation slippage can also be caused by clay-rich soil that naturally expands as it absorbs moisture. This type of ground pressure often damages foundations on flat sites. On a sloping site, soil expansion generally causes downslope thrust against the foundation.
Tiebacks and Tiebeams solve foundation problems
A foundation repair contractor is the best professional for diagnosing and repairing slipped foundations on a sloped site. Helical ties and tie beams are possible solutions to stop slippage and restore foundation stability.
A helical mooring is a steel anchor fitted with helical plates that allow technicians to drive the anchor into the ground like a giant screw. A series of these anchors are usually driven through the foundation wall on the uphill side of the house and sunk deep into the ground. Such an installation effectively nails the upper foundation wall into the slope. The same repair technique is used to stabilize and restore retaining walls that lean due to ground pressure.
Since it is usually the foundation wall on the downslope side of the house that slides down, the repair strategy often involves installing joists to connect the stable upslope wall to the downslope wall. The combination of ties and tie beams is a commonly used repair strategy. However, the foundation specialist will likely suggest other repair work to help control drainage so the soil around the house doesn’t become too heavy or too saturated.
