SLAB ON GRADE DESIGN FOR EXPANSIVE SOILS 2

[alumpkin]

Generally looking for some guidance on how to design slab on grade for expansive soils. Geotech is recommending a monolithic grade beam stiffened non-structural slab supported by straight shaft piers. The recommendation is to remove the top 5 feet or so of the expansive clays. Below these clays are soft limestone with clay seams. These top five feet are replaced with compacted structural fill installed in lifts. The grade beam system is about 4 feet deep and 2 feet wide. So, here are my questions:

1. What expansive loads are used to design the slab?
2. Do you design the slab as typically would for the uniform and point loads and disregard the expansive loads since you have removed the most problematic clays and installed a grade beam system?
3. Design as a two-way plate?
3. From what I can determine online this is a complicated problem and not much data is out there for practical use.

Any thoughts would be appreciated!

alumpkin
CU 1982


Alan L. Lumpkin, MS, PE
Greenville, SC

 

[alumpkin]

Guys,

By the way, the Geotech recommendation id for 1" movement.

Alan L. Lumpkin, MS, PE
Greenville, SC

 

[dik]

So a SOG on engineered fill will likely work. You need his recommendation that building it on fill will keep movement to this limit.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[JoelTXCive]

Alan - fyi.... The Foundation Performance Association is the professional group here in the Houston area. (I'm a member)

It's membership includes Geotech & Structural Engineers, along with contractors and suppliers.

If you need any of their other documents...Just request them here and I think I can get them for you.

 

[alumpkin]

Hi Joel,

YES! I found it and have downloaded some of documents and will begin studying these.

@DIK, So how does structural fill discount any upward movement of the deeper limestone and clay soils? If they move upward will not the structural fill go for the ride and exert pressure against the SOG?

Alan L. Lumpkin, MS, PE
Greenville, SC

 

[jayrod12]

It is likely that the soil deeper down will not go through the same volumetric changes as the conditions at depth, i.e. temperature and moisture content, tend to stay relatively stable.

 

[alumpkin]

OK...that makes sense. Thanks.

Alan L. Lumpkin, MS, PE
Greenville, SC

 

[dik]

Good properly compacted fill doesn't, but if you are limited to 1" of movement (can be settlement, too), there could be some issues... if in Texas, you likley do not have to concern yourself with frost heave. The geotekkie should confirm that the max movement will be limited to 1".

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik