High Uplift forces in shallow foundations

[Okiryu]

Hi, what can be the best options to deal with high uplift forces in shallow foundations? This is a warehouse. Soils are unsaturated medium stiff to stiff elastic silts. I am thinking on increasing Df so I can get more overburden on the footing. Thanks in advance for your opinions.

 

[Lomarandil]

I don't know enough to say it's the best option, but increasing Df or the thickness of your footing are some of the simplest solutions, and ones that I see implemented regularly. Then it's just a matter of determining which is more expensive, more excavation (consider if dewatering will be req'd) or more mass concrete.

 

[oldestguy]

I suspect your need for this resistance is when weather is rough. Many times this is during heavy rainfall events and sometimes the ground water has high elevations, meaning soil density is its submerged unit weight, significantly reducing its effectiveness. Same would go for the footing unit weight, no longer 150 pcf.

 

[Okiryu]

OG, actually I got high uplifts from the structural analysis from the structural engineers. I assuming that because it is a warehouse with large spans and openings, uplift forces due to wind are high. I am also located in a quite active seismic area. Groundwater is deep (more than 5 meters below ground surface). We may need to go for short helical piles if uplift is really high. Thanks again for the input.

 

[JoshPlumSE]

Put the footing deeper so that you have more soil overburden on top. Increase the size or thickness of the footing. Or, use a grade beam to tie it to a nearby adjacent footing (i.e. make it into a combined footing).

Combined footings work great when you're tying the two columns in the frame together, because the one in compression will really help to stabilize the one that went into tension.

 

[Okiryu]

Thanks for the responses. I have to look at the plans but since we may not have columns closely spaced perhaps combined footings will be difficult to implement. Anyways, as always thanks for your opinions.k