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The items below are signs you can look for to
determine possible expansive soil related movement. The
probability that your foundation has experienced some
movement increases with the number of indicators observed,
their frequency and location in the structure.
Exterior Indicators:
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Diagonal (stair-stepping) Cracks in
brick walls. Cracks may go through brick or mortar
and vary in width.
-
Sagging brick lines when sighting
along a wall.
-
Bowed or non-vertical walls.
-
Separation of wood trim joints at
corners.
-
Separation of concrete driveway,
patio, or sidewalk from foundation.
-
Tilting of landscaping/retaining
walls.
Interior Indicators:
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Cracks in sheetrock walls or
ceilings.
-
Bowed or non-vertical walls.
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Bottom of wall separating from the
floor.
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Cracks at wall corners.
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Cracks above doors.
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Sticking doors. (warped door frames)
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Sticking windows.
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Sloping floor surface.
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Cracks in ceramic or vinyl tile.
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Cracks in concrete floor 1/16th inch across or
wider.
Soil Moisture Changes
Observing soil moisture changes around your
foundation is possible, but what about under it? Moisture
can move from outside to under your foundation through a
property of soils known as suction. Soil suction is similar
to placing just a corner of a dry, compressed sponge in
contact with a puddle of water. In a short time, the sponge
has drawn water throughout itself and grown in volume. While
a water source is present, the sponge will continue to
absorb water until it is saturated. If the water source is
cut-off, then water already in the sponge will distribute
itself evenly, but the sponge will not reach saturation.
Water can move horizontally and vertically through the soils
under your foundation in a similar manner. As clayey soils
draw water to themselves, they too grow in volume (swell or
heave) causing your foundation to move. Drying outside your
foundation reverses the process. The moist soils will lose
volume (shrink) as soil moisture moves out from under your
foundation causing the foundation to settle. Shrinking and
swelling soil motions can lead to damaging your foundation
and structure. Uniform changes in soil moisture are less
damaging to your structure than localized changes.
Several sources of soil moisture changes are provided in the
following table. You should review the list and possible
actions to control or minimize the various sources. Begin
practicing the suggested actions as soon as possible to
improve your foundation and structure performance. Many of
these actions can become a routine part of your ongoing
conscientious owner maintenance activities. Annually inspect
the area within 5 feet of all sides of your foundation after
a rain to determine if proper drainage is maintained away
from your structure. Monitor existing cracks for progressive
or seasonal movements. Some of the possible actions,
suggested in the accompanying table, will require an expert
for assistance.
Living With Expansive Soils Action Plan
|
TYPICAL SOURCES |
POSSIBLE PROBLEMS |
POSSIBLE ACTIONS
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Rainfall |
Non-uniform runoff from roof may
result in localized heave.
|
Maintain soil sloping away from all
sides of the foundation for a
distance of at least 5 feet, use
gutters with downspouts that
discharge at least 3 feet from the
foundation.
|
|
Gutter Down Spout |
Concentrated sources of water may
lead to non-uniform foundation
movements. |
Extend discharge a minimum of 3 feet
from the foundation and use splash
blocks to avoid erosion or use
flexible discharge tubes.
|
|
Poor
Drainage
|
Localized source of water from
rainwater flowing or ponding next to
the foundation may lead to localized
heave of the foundation.
|
Slope
ground away from all sides of the
foundation for a distance of at
least 5 feet, create drainage swales
to divert water away from the
foundation, keep dirt line several
inches below the brick line, use
clay soil fill to create positive
slope away from the foundation. Do
not use SANDY SOILS for fill next to
foundation, use CLAYS. Compact the
fill to shed water, not absorb it.
|
|
Flower Beds
|
Localized source of water not on all
sides of foundation, may result in
non-uniform foundation movements.
|
Do
not flood or pond irrigation water,
slope ground surface away from the
foundation, do not trap water near
the foundation with edging, use
mulch to slow evaporation.
|
|
Sprinkler Valves |
Valves frequently leak and joints
may leak with time, resulting in
localized water sources which may
cause non-uniform foundation
movements. |
Locate at least 5 feet from
foundation and inspect valves
frequently.
|
|
Over
Watering |
Provides excess source of soil water
for suction to draw moisture under
foundation which may cause a stable
area to begin heaving and damaging
your structure. |
Water
just enough to keep plants and grass
alive and growing, not thriving and
lush through saturating the ground.
|
|
A/C
Unit Condensation |
Concentrated source of water which
can result in non-uniform foundation
movements. |
Direct the discharge line to drip on
a concrete pad or splash block which
has been properly sloped away from
the foundation.
|
|
Hot
and Dry Climate |
Loss
of soil moisture from under
foundation edges may cause
foundation settlement.
|
Uniformly water landscape planting
and area next to all sides of the
foundation, install automatic
sprinkler systems, add sidewalks
adjacent to the foundation.
|
|
Excess Drying on the West Side /
Non-uniform Moisture Loss
|
Non-uniform drying on all sides of
foundation from the sun or failure
to provide watering on all sides of
the foundation may cause non-uniform
foundation movements.
|
Apply
more landscape water on drier sides
of the foundation, use mulch to slow
evaporative drying, plant quality
shade trees along with installation
of a tree root/vertical moisture
barrier.
|
|
Trees
|
Tree
roots grow under foundation and dry
out soils causing non-uniform
foundation settlements.
|
Plant
tree a distance greater than their
mature height from the foundation.
If existing trees are closer-install
an approximately 4- foot deep tree
root/vertical moisture barrier
system near the foundation and
possibly prune trees (to limit
moisture stress) if barrier system
is under the drip line of the tree.
Water tree roots away from the
foundation.
|
|
Landscape Planting |
Drying from roots, transpiration and
soil suction may cause non-uniform
foundation movements.
|
Plant
bushes and shrubs away from the
foundation, uniformly water plants,
do not flood or pond water next to
the foundation.
|
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Landscape / Retaining Walls
|
Non-uniform drying on all sides of
foundation may result in non-uniform
foundation settlements.
|
Apply
more landscape water than other
sides of the foundation, use mulch
to slow evaporation.
|
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Plumbing Line Leaks |
Leaks
in sewer or water lines provides
localized source of water that may
lead to localized foundation
movements. |
Monitor water bills, get leak
detection plumber to isolate and
repair leaks, verify repairs with
pressure tests.
|
|
Shallow Subsurface Seepage / Moving
Down Slope |
Concentrated source of water to
foundation soils may result in
non-uniform heave of the foundation.
|
Install interceptor trench drain up
slope to collect and divert seepage
water around foundation soils and
discharge down slope or to a sump.
|
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Moisture Vapor Rising from Wetter
Soil Beneath Foundation
|
Gradual and uniform rise in soil
moisture under foundation may lead
to gradual heave of structure.
|
Normal occurrence, foundation
stiffness should be designed and
constructed for this long term
condition.
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Additional information on all of these items can be obtained
in the excellent reference, So Your Home is Built On
Expansive Soils, A Discussion of How Expansive Soils Affect
Buildings, edited by Warren Wray, Ph.D., PE., published in
1995 by The American Society of Civil Engineers. This 54
page booklet can be obtained for approximately $20.00 by
calling ASCE publications at (800) 548-2723. |
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