of Foundation Problems
Water is the main enemy in expansive soils problems.
There is either too much water, causing the soil to
swell, or not enough, causing the soil to shrink.
If all soils beneath a foundation swells uniformly
or shrinks uniformly it is unlikely to cause a problem.
But when only part of the foundation heaves or settles,
differential movement causes cracks and other damage.
movement is caused by differences in soils moisture.
After construction, soil beneath part of the foundation
becomes wetter or drier than the rest of the soil.
Here is why this happens:
1. When there is a gain in soil moisture:
This is the most serious threat since the swelling
potential of expansive soils is much greater than
the shrinkage potential. Moisture gain can come from
plumbing leaks, subsurface water like wet weather
or a high water table, or surface water. Surface
water is improper drainage of landscape water or
Poor drainage can be a major contributor to soil
moisture gains. Roof runoff should be directed
away from the house through the
use of gutters. Gutter downspouts should not be permitted to
discharge the water next to the foundation. Surface
drainage next to the
foundation should slope away from the house approximately ¼ " per
2. When there is a loss of soil moisture:
The soil may be at or near its optimum moisture content when the
foundation is built, but it may lose enough moisture during a drought
to cause the foundation to settle. Settlement is usually greatest
near the perimeter of the foundation where the soil dries most
3. Extremely low or high soil moisture during construction:
If the soil content is very low when a slab-on-grade foundation
is poured, soil to the slab edges regains moisture first because
it is directly exposed to rain water or irrigation water.
If the soil moisture is extremely high during construction, the
slab will hold in the moisture except at the perimeter, where it
is exposed to more wind and heat. In cases like this the slab edge
loses moisture at a different rate than the soils under the house
and the house will settle.
4. Poor Pre-Construction Compaction of the building
depend on the uppermost soil layers to provide bearing
capacity to support the structure and keep the foundation
stable. If the bearing soil was not compacted properly
during grading, the foundation is subject to settlement
as the supporting soil consolidates.
Also of concern is when a
structure is supported by various soil conditions.
In this case the house may settle differentially .
As an example, if one half of the foundation sits upon
expansive clay and the other half bears on select fill
and/or rock, the amount of seasonal movement will vary
from one half to the other half. If the foundation
system is not properly designed, the differential movement
may cause damage to the foundation and structure.
your foundation professionally evaluated at
no charge. Contact our office to schedule
an appointment with one of trained technicians