PTI for Collapsible Soils

[gandersen]

Greetings:

I recently came across a situation in Albuquerque, New Mexico where geotechnical recommendations were made for post tensioned slabs in a condition where collapsible soils are present and the maximum amount of settlement was estimated to be in the range of 2.5 inches. The designer used the latest version of the PTI program and the foundations have not performed well.

When I asked the designer about the length that he used (distance overwhich the 2.5 inches of settlement was assumed to occur), he told me that parameter is not part of the input in the new program.

I assume that the PTI program is based on expansive soil behavior and that the "characteristic" length is inherent in the program (based upon the typical lengths for moisture penetration and drying at the edge of the foundation).

Can someone help me to find information on whether or not the PTI program is applicable to collapsible soils and how the designer is supposed to incorporate a settlement estimate due to collapse?

Thanks in advance.

Glen

Glen Andersen, Sc.D., P.E.
Kleinfelder, Inc.
Albuquerque, New Mexico

 

[fndn]

As you know, Dr. Anderson collapsible soils can not be solved by Structural design techniques. You may have more answers if you post it in the Structural Engineering forum or try to call the software maker directly.

In California, we just hack away at the affected depth and try to compact at higher moisture and density. Is your approach different at your localle?