Ignoring Water?

[dcarr82775]

I was having a discussion with the regional engineer for a rather large nationwide firm. He told me that he 'ignores' the affects of water table on the embedded portion of cantilever soldier beams (uses a moist unit weight instead of a submerged unit weight). Does anyone know of a rational for that?

 

[killswitchengage]

Well, if the soil is submerged follows Terzaghi's notion about bearing capacity of a footing with saturated soil that is ( i forgot the notion i think you divide the bearing capacity by 2)

 

[dcarr82775]

I have always taken a buoyant weight of soil for passive resistance below water table. I was not familiar with Terzaghi's 1/2 notion, but it makes sense to me in a basic way. I have simply never heard of someone flat out knowingly ignoring the effects of groundwater on passive resistance in soils.

 

[PEinc]

If buoyant soil weighs half as much, passive pressure is half also. I don't see how you can ignore buoyant weight. That being said, there is more going on with soldier beam embedment than just passive pressure. Soldier beam embedment design is a rather empirical process. Shorter soldier beam embedments often work but are hard to prove on paper and are even harder to get approved by a submission reviewer when design references are few.

http://www.PeirceEngineering.com

 

[killswitchengage]

If the soil is saturated and is flowing toward a given axis , then take the saturated density and insert the PWP in the shear strength equation
by doing so you will acknowledge the buoyancy and the flow force of water .