Drought condition impact on new slab

[netknight]

We are experiencing a drought condition in Dallas that has left the area without rain for 60+ days. I am about start construction on a large home that will be on a "engineered" post tensioned slab on piers. The soil is black clay and I am concerned about the possibility of heaving once the water returns to the soil. Comments?

 

[TimC]

The problems with swelling clays in Texas are sufficient to be noted in many foundation engineering text books -- so your concerns are probably well justified. Given that it is a regional problem you would do well to contact a local geotechnical consultant to review the plans, and if warranted, test the soils.

 

[ishvaaag]

You may try lift the slab from the soil by interposing a styrodur layer as thick as the heave usually there expected, or altogether in the air. In any case I would review the reinforcement for such circumstance.

 

[sc]

I'm not sure about the actual conditions you may experience in Dallas but in Mildura (Australia) we generally define our region as arid and hence design for up to 70mm of soil movement.

One method of preparing the site during dry weather is to build a small bund wall around the building perimeter and soak the area of the building foundation for a period of time to boost the soil water content and hence reducing the impact of heave. To be fully effective we generally need to have a damp follow up period after construction. If this is unlikely then try wetting the perimeter of the new building to help retain some moisture in the soil.

Regards

sc