Point of zero shear on laterally loaded pile

[tmoe]

Happy New Years Eave everyone. I have a question that I know is relatively basic, but I cant seem to wrap my head around.

At the most basic level of my design, I have a pile that will be embedded into native soil some distance to be determined. It will also be exposed about ground a distance of about 5.5 ft, and functioning as a retaining element of wall. I need to stress that this is a SMALL project and Im not looking for a rigorous driven pile analysis. for now using the embedded pole formula in Enercalc and the California Building Code is just fine. I am curious though how to approach a simplified bending design for the pile. My mentor gave me the following instructions before he left out of the country on vacation:

" Resolve the the forces on the retaining side of the wall such as active pressure, surcharge, wind load if applicable, into a resultant force. Do the same for the passive pressure side. Now determine the location of the point of zero shear. This is where the moment will be maximum. Design the post for bending based on this moment."

My confusion is that when I draw a simply picture of this scenario, I'm not sure what assumptions Im making in terms of where this pile is supported. Am I assuming pinned supports? If so where. As is, all I see is a vertical beam with two unequal loads, both of which will cause the pile to rotate counterclockwise.

Can you guys help me resolve this confusion?

 

[Ron]

It is the point of fixity for the cantilevered condition

 

[FixedEarth]

You are very colose to your answer. In your loading diagram, you can compute Active thrust and Passive thrust for a simple triangle - get rid of the constant passive at depth, you won't need it for a short retaining wall.

Then set Pa = Pp. Take moment at - 5.5 ft and compute embedment depth D to make Pa and Pp equal to each other. This D is the location of your maximum moment. It should be about 0.6H or about 3.3 ft for your 5.5 ft retaining wall.

Remember to incorporate pile spacing into your Active thrust & Pile sapcing and 2.5 multiplier for your Passive resistance.

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