Passive Earth Pressures in Building Foundation Design

[cpdonahue]

I am a geotech engineer being asked to provide passive earth pressure parameters for the design of building foundations. Metal building supported by column footers. Is it conventional to use passive earth pressures for lateral loads on foundations, or is the lateral load typically addressed with shear? Is it appropriate to provide these values to the structural engineer for this application, or do I advise on the limits of their application?

 

[TigerGuy]

Passive pressure is the resisting pressure provided on the side of the footing element against footing movement. The structural engineer needs to know the allowable passive pressure so they can design the footing large enough to achieve the equal and opposite force from the passive soil pressure.

 

[EireChch]

It depends on how deep the footings are and how much movement the struct engineer is willing to accept.

ps footings not footers.

 

[cpdonahue]

TigerGuy,
It has been indicated to me that they intend to use these values to accommodate lateral loads on the foundations (resisting the footing wanting to kick-out). I have never been asked for earth pressures for shallow foundation design (except for retaining walls) in 10 years....
Passive pressures also require mobilization, which I don't think you want on a building footing...

 

[cpdonahue]

EireChch (Geotechnical

Is it your experience to provide earth pressure values for footer design, and if so what restrictions/limits on application do you provide?

Footer/Foundation/Footing - all used interchangeably where I live

 

[Celt83]

At a minimum we typically need to know the following for every project, not just retaining walls:
- Soil Density, saturated unit weight
- Soil Friction Coeff.
- At-Rest Pressure Coeff (Ko)
- Active Pressure Coeff (Ka)
- Passive Pressure Coeff (Kp)
- Subgrade reaction for slabs on ground

Speaking directly to the engineer's use of Kp for global sliding stability of the building, I'd typically only utilize that for seismic lateral resistance as the movement permitted under seismic is usually pretty high. For Wind and any incidental lateral loads generated from the framing layout I tend to first try and only utilize friction and if really needed use At-Rest pressures.

Most geotechnical reports I'm seeing these days don't include any of this information and it is generally needed for the perimeter foundation designs even for at grade structures and global sliding stability checks.