Effect of Water table for Shallow Foundations

[maximus808]

If the water table is at the bottom of the a shallow footing, does do we need to use the modified equation? Or the general ult. bearing capacity equation will be sufficient. Thanks.

 

[civilized_naah]

If the water table is at the bottom of the a shallow footing, does do we need to use the modified equation? Or the general ult. bearing capacity equation will be sufficient. Thanks.

For a footing with dimension B, the groundwater DOES NOT AFFECT the bearing capacity if the water table is deeper than B below the bottom of the footing. If the GWT is shallower than that, one of more of the last 2 terms (not the cohesion term) are affected (reduced)

 

[boo]

If the water table is at the bottom of the a shallow footing, does do we need to use the modified equation? Or the general ult. bearing capacity equation will be sufficient. Thanks.

see ATTACH help you

GEO.doc

 

[maximus808]

Thanks Boo.

So basically there are three factors to a typical bearing capacity problem with water table.

You have the cohesion part, base part, and depth part.

Using the effective unit weight method, if the water table is at the middle of the base and surface, the depth portion of the equation is simply Gamma Total (Total Depth of Footing) - Gamma Water (Total Depth of Water). As if I was calculating the effective unit weight of water.

Or I guess for the depth factor portion, it you could break up the areas of depth into D*Total Unit Weight (where D is the portion above the water table, and d*Total Unit Weight - Unit Weight of Water) where d is the depth of the Water table to the bottom of footing.

Let me know if you guys think I'm on the right track. Thanks.