Foundation Settlement Problems in Huntsville
By James A. "Buck" Durham, P.E.
The topography of much of Huntsville consists of moderate to steeply sloping, wooded hillsides which
generally have a shallow bedrock depth- this is especially true in areas where numerous boulders or
bedrock pinnacles outcrop at the ground surface. House construction in this type of terrain usually requires
extensive land clearing and the addition of fill soil to provide a level pad or acceptable base on which to
construct footing and foundation walls. Moreover, because of the ground slope, houses are often
constructed on crawl space foundations which bear on footings that stair-step "up and down" the natural
and/or "artificially created" grade. Many times the footings are founded partly on rock and partly on soil. If
the soil-supported footings settle and the rock supported footings do not, a differential settlement has
occurred. Differential settlements are frequently the cause of foundation wall and brick veneer cracking;
they are exemplified by stair-step crack patterns and/or crack patterns which indicate rotation or pivoting
about a central point.
Foundation settlements occur whenever the bearing pressure of the foundation footing exceeds the
strength of the supporting soil. Settlements also occur if the supporting soils are fill soils that have not
been properly compacted, or if the underlying soils include mixed organics (vegetation) that decay over
time. It is not unusual for foundations to rest on large tree stumps or root systems that were cut to the
ground level.
Another common cause of foundation settlement or movement in the Huntsville area is associated with
underlying subgrade soils. These soils are usually residual clays that have evolved from weathered
limestone bedrock. Geo-technical engineers classify these soils as "highly plastic" since they behave
"actively" over a wide range of moisture contents. Plastic soils physically shrink in volume when they dry or
desiccate, and swell in volume when they become wet. Inevitably, during the summer months foundations
tend to settle, causing cracks in foundations and brick veneer; during the winter months the cracks
disappear. Proper site drainage is imperative in this geologic/topographic area because the soils should
maintain a uniform moisture content. If water stands or collects in low lying areas near foundation walls,
the subgrade soils can become and/or remain saturated even as adjacent soils dry.
Regardless of the cause, the potential for long term differential foundation settlement is very good in the
Huntsville area. Thus, in new house construction, it is imperative that footings are located on stiff
underlying subgrade soils- preferably deep in the ground, below seasonal drying penetration-and that
proper drainage is provided to prevent water from standing and soaking into the ground around the home
(saturating the supporting subgrade soils). Of equal concern is water that flows along the foundation walls;
it can lead to erosion undermining.
A conscientious effort has been made by the authors to provide accurate information; however, neither the
authors nor Alabama Residential Inspection Services, LLC will assume any liability for its use. Readers are
advised to perform additional research, seek other professional advice, and to act on the information
provided, herein, very carefully.
By James A. "Buck" Durham, P.E.
The topography of much of Huntsville consists of moderate to steeply sloping, wooded hillsides which
generally have a shallow bedrock depth- this is especially true in areas where numerous boulders or
bedrock pinnacles outcrop at the ground surface. House construction in this type of terrain usually requires
extensive land clearing and the addition of fill soil to provide a level pad or acceptable base on which to
construct footing and foundation walls. Moreover, because of the ground slope, houses are often
constructed on crawl space foundations which bear on footings that stair-step "up and down" the natural
and/or "artificially created" grade. Many times the footings are founded partly on rock and partly on soil. If
the soil-supported footings settle and the rock supported footings do not, a differential settlement has
occurred. Differential settlements are frequently the cause of foundation wall and brick veneer cracking;
they are exemplified by stair-step crack patterns and/or crack patterns which indicate rotation or pivoting
about a central point.
Foundation settlements occur whenever the bearing pressure of the foundation footing exceeds the
strength of the supporting soil. Settlements also occur if the supporting soils are fill soils that have not
been properly compacted, or if the underlying soils include mixed organics (vegetation) that decay over
time. It is not unusual for foundations to rest on large tree stumps or root systems that were cut to the
ground level.
Another common cause of foundation settlement or movement in the Huntsville area is associated with
underlying subgrade soils. These soils are usually residual clays that have evolved from weathered
limestone bedrock. Geo-technical engineers classify these soils as "highly plastic" since they behave
"actively" over a wide range of moisture contents. Plastic soils physically shrink in volume when they dry or
desiccate, and swell in volume when they become wet. Inevitably, during the summer months foundations
tend to settle, causing cracks in foundations and brick veneer; during the winter months the cracks
disappear. Proper site drainage is imperative in this geologic/topographic area because the soils should
maintain a uniform moisture content. If water stands or collects in low lying areas near foundation walls,
the subgrade soils can become and/or remain saturated even as adjacent soils dry.
Regardless of the cause, the potential for long term differential foundation settlement is very good in the
Huntsville area. Thus, in new house construction, it is imperative that footings are located on stiff
underlying subgrade soils- preferably deep in the ground, below seasonal drying penetration-and that
proper drainage is provided to prevent water from standing and soaking into the ground around the home
(saturating the supporting subgrade soils). Of equal concern is water that flows along the foundation walls;
it can lead to erosion undermining.
A conscientious effort has been made by the authors to provide accurate information; however, neither the
authors nor Alabama Residential Inspection Services, LLC will assume any liability for its use. Readers are
advised to perform additional research, seek other professional advice, and to act on the information
provided, herein, very carefully.
Foundation Settlement
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