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Footing on a Slope

Footing on a Slope

Footing on a Slope

Hello Engineers,

The only reference that I have found that deals with bearing capacities for footings near slopes or on slopes is NAVFAC 7.02 "Foundations and Earth Structures".

It says if the footing is far from slope, bearing capacity can be considered as any bearing capacity equation on level ground condition.

What is not clear to me is when the engineer can decide if the footing is close or far from the slope. There are no clear directions.

In my case, i am working on a project which the slope is about 40 m high (on a hill) and the plan is to build an edge of a building which is about 10 m from the edge of the slope. I am not sure which approach to use. I could use the one "near" the slope and be more conservative however I would like to have a criteria when to assume the footing to be near or far from a slope.

Please advise.

RE: Footing on a Slope

is the existing "hill" stable? how steep is it and is the slope at risk of sliding?
suggest that it be evaluated (using global stability) before you make your decision on how far your building is set back.

RE: Footing on a Slope

There are two issues here:

1 - reduction in bearing capacity due to slope
2 - risk of slope instability affecting foundation.

if the slope is 40m high and you are 10m from it then you definitely need to do a global stability check as cvg recommends.

Also, Das' book is a good reference for foundations near sloping ground. you can review the tables and determine the distance at which the slope has no effect.

RE: Footing on a Slope

Thanks a lot for your responses.

See attached the charts by DAS, which are originally from NAVFAC VOL 2.

b = the distance between the footing and the edge of the slope.

B = footing width.

The chart uses b/B ratio. As you can see, the max b/B value is 6. So if you have a b = 10 m, and B = 0.8 m, b/B = 10/0.8 = 12.5. Based on this, can you consider the footing to be far from the slope?

I understand that you need to run a slope stability analysis, regardless, BUT from the "near" or "far" point of view, would you consider the footing far from the slope?

RE: Footing on a Slope

It's not really related to the extents of the chart, more about when the curve for your given slope angle (β) reaches the horizontal line representing a slope at 0*. If b/B for your footing is larger than this intercept, your footing is sufficiently far from the slope that the effect is negligible.

(e.g. for a frictional soil with phi = 30* and Df/B=0, the you could consider the footing "far" from a 30* slope at b/B=2)

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