Failure of Highly eccentric footing

[civeng80]

On a cohesive soil such as a clay the strip footing fails by shear on the shear plane. Safe bearing capacity found from field measurement of undrained cohesion and then Terzaghi’s equations or multiply Cu by 2 say.
Now we have a highly eccentric strip footing where most of the pressure is on the edge.
So now we apply a load until failure, how would footing fail ? And would it relate to bearing pressure mentioned above?

 

[msquared48]

Probably rotational failure, similar to the rotational failure of a hillside.

Mike McCann, PE, SE (WA)

 

[Ron]

Agree with Mike. You have effectively reduced the size of your footing to the edge and will result in a shear failure circle along that edge in rotation.

 

[civeng80]

So still a shear failure at the edge,but more localised ?

 

[msquared48]

Hardly localized if the entire footing rotates.

Mike McCann, PE, SE (WA)

 

[KootK]

I guess it would depend on how eccentric this highly eccentric strip footing really is. Most of them are relatively rigid and are restrained from significant rotation via moment connection to the walls that they support. In these cases, I would expect the soil failure to be identical to what would occur with a concentric strip footing.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Panars]

The traditional way to analyze the bearing capacity of an eccentrically loaded footing is to reduce the effective width of the footing due to the eccentricity. So if the eccentricity, e, is 2 m, and your footing width is 12 meters, the effective footing width would be W-2e, 12 - 2*2 = 8 m. The tendency to rotate would cause a shear failure on the side with the greater pressure.