SOILS AND FOUNDATIONS

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OVERVIEW

A familiar saying is that a house is only as good as the foundation it is built on.  Well that is only partially true because a foundation is only as good as the soil it is built in.  Unstable soil is always moving and If a foundation is built on an unstable substructure it is only a matter of time before a foundation failure occurs.  This foundation catastrophe is extremely expensive to fix and many new homes begin to have serious foundation problems within 5 years of construction due to inferior foundation systems. 

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SOILS

There are many soil types found in Texas but the most predominate types are as follows:

• Clay
• Sand
• Sandy Loam
• Limestone 

Not all soil types are created equal in regards to how foundations react to differing soil conditions.  If the wrong foundation is built in an unstable soil type such as clay the long term consequences can be catastrophic.  In many cases by the time the harmful affects start to show it can be beyond the terms of warranty of a typical construction contract.  Your best defense is to have a soils test performed by a licensed soils engineer.

A licensed Soils engineer will bore a 12" to 18"  hole into the soil and take soil samples all the way down to a stable soil substrate.  The soil samples are then taken to the lab and tested for expandable properties among other things.  Once their testing is completed they produce a report and a recommendation of the the most suitable foundation system to be employed.

This will not always mitigate 100% of the risk because no one can guarantee the future movement of the earth but it will give the best possible foundation scenario.

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 FOUNDATION OPTIONS

  Post-Tension Foundation System

The Post-Tension Foundation System consists of a cable that has a plastic jacket to help the cable slide when it is tightened.  On one end it has a steel plate that is embedded in the foundation wall.  On the opposite end it has a another steel plate and a nut that is exposed on the foundation wall. 

 After the concrete is poured, the nut is tightened thus providing the tension needed to hold the foundation together.  Too much tension and the cables can snap.  Too little tension and it looses its effectiveness.  There is no reinforced steel in the footing and stem wall to strengthen the concrete. 

 The cables are laid out in a grid held up by a small stand so the cable is in the center of the slab.  In this system there is no reinforced steel what so ever.  The foundation footings are not reinforced and very susceptible to cracking and falling apart.  Over the life of the foundation the cables are to be inspected and adjusted, but an unsuspecting home owner will never know.  When the foundation fails they assume the blame for not preforming the required maintenance.

Reinforced Steel Foundation System

This foundation system is a typical foundation that is utilized in most areas of the country.  It is far superior to the post-tension system but again it is susceptible to the conditions of the soil.  The deeper into the soil substrate the foundation structure is constructed, the higher the success rate becomes.

As you can see in the reinforced steel foundation, a lot more steel is used and is infinitely stronger.  This system also has a series of interior footings that are also reinforced.  It does take a lot of reinforced steel as well as labor to construct but so much more cost effective than repairing a failed system which can run tens of thousands of dollars.

 As shown by the diagram, the steel reinforced foundation is deeper into the soil and has a lot of steel to strengthen the concrete.  Over time many soil types can shift due to weather conditions and the movement of the earth.  A foundation with significant steel will contribute to holding the concrete together under many circumstances.

Caisson & Grade Beam Foundation

 

 The Caisson & Grade Beam foundation provides the best protection in an unstable soil conditions.  It is also the most expensive system as well.  This option may not be required in all unstable soil conditions depending on the results form soils testing.

 A series of auger holes are bored down through the unstable soil to stable soil. A reinforced steel cage is lowered down into the hole and then filled with concrete.  A reinforced steel and concrete foundation beam is formed linking all the caissons together to form an extremely ridged and stable grid that is resting on the stable soil below.  In this case no matter what the unstable soil does, it will not affect the foundation.

CONCLUSION

It is always advisable to consult with a soils engineer to determine the best foundation option for the soils on any given property.  There exists a thriving industry fixing foundations for homes with unsustainable foundations where the price tag can be upwards of tens of thousands of dollars.  The solution to this problem is in the beginning with proper soils testing and foundation engineering to provide a strong and sustainable home to last into the next century. 

At Woodscape Homes our quality starts in the ground

 and works it's way to the top.