SD ENGINEERING



Civil and Structural
Engineering Services
Related to:
- Floor slab crack repair
- Raised foundation repair / replacement
- Foundation underpinning and releveling
- Drainage improvements
- HUD foundation compliance reports for manufactured home financing

Gary Sniffin

Civil Engineer
C-29710

Tel.:
(619) 258-0416

Address:

PO Box 711661
Santee, CA 92072


E-mail:


FOUNDATION MOVEMENT
The foundation is the main support of the house.  It is the substructure upon which the superstructure rests.  The foundation includes the footings, foundation walls, columns, slab, and all other parts that provide the support for the house and transmit the load of the structure to the underlying earth.  The safety and usability of a house is determined by its structural integrity. In many cases, foundation movement is minor and the problem(s) can be easily corrected.  In other cases, the movement is significant and causes damage to the foundation and the superstructure of the property.
There are many reasons for foundation movement and apply to both slab-on-grade and raised foundation homes.  No two buildings are identical.  Each one is subject to an enormous range of variables ranging from the weather on the day the property was built down to the last time it rained.  Even in San Diego, where the average rainfall is less than 10” per year, moisture can have a significant impact on the performance of a foundation.  The major causes of foundation problems are as follows:

Expansive Clay Soils

Clay soils have very small cohesive particles and can expand dramatically when the moisture content increases due to rain, plumbing leaks, excessive watering, poor drainage, etc. These conditions can cause upward pressure and stress to the foundation. Conversely, soils can also “dry out” during droughts and other times without measurable moisture.  When the amount of expansion / contraction of the soil is great enough, it puts tremendous stress on the foundation system. In order to minimize possible foundation stress, consistent soil moisture levels are required.  It is the changes in the moisture levels resulting in shrinkage and swelling in expansive soils which cause the foundation to settle or heave.

Soil Compaction and Fill Soils


Many homes in San Diego, particularly the older homes, were constructed before there were modern grading standards and rigid soil compaction testing requirements.  A lot of these homes were built on cut and fill lots, where the original native soil was removed to make a flat building space or soil from another location was brought to the building site.  In either case, when the soil was not properly compacted, over time the soil would settle excessively and cause the foundation to settle along with the soil.  Also, many of the fill soils were of the expansive type and when moisture was continually added to the fill soils, they expand. This effect is called upheaval. In addition to the primary structure, driveways, patios, and other concrete flatwork around the property can also experience settling, cracking, and other signs of distress.

Drainage
and Water Leaks

Drainage issues can create low spots and allow water to penetrate under the foundation. This can cause the soil to move out from underneath the slab.  The principal of positive drainage dictates that the surface and subsurface water is diverted away from the foundation of the home and transported away from the property.  Gutters with downspouts that discharge water 5 feet away from the foundation are a good start.   Broken plumbing lines or leaking sprinkler pipes can easily cause damage because they are difficult to detect until after they have cause some signs of visible damage. 

Tree Roots


Trees can also have an impact on the foundation.  When the tree root system encounters soil beneath the foundation, they utilize this as an additional water source during the drier seasons to supplement their moisture needs.  As these roots grow, they can heave a stemwall or push up a concrete slab.

Workmanship Quality and Materials


The “what and how” at the time of construction can have a very significant impact on the ability of the foundation to perform as was designed. Was the reinforcing steel adequate?  Was it place to close to the edge of the concrete?  Was the concrete mixed properly, spread evenly and allowed to cure correctly? Many of these considerations and more, when coupled with soil and moisture issues addressed above, can all influence how a foundation performs.   

 

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