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Retaining Wall on Basement Wall

psychedomination

Structural
Jan 21, 2016
119
Hi there,

I'm working on a project where there will be a retaining wall on top of a cesspit wall. See below :

Retaining Wall Basement Wall  - Copy.jpg

I will check the wall stem reinforcement and design it accordingly. However, I am wondering what global checks need to be done (overturning/sliding) as this seems similar to a basement wall configuration.

Sliding for cross-section B-B should be fine as there is an equal force on both sides, so there shouldn't be any unbalanced forces. However, in cross-section A-A, the lateral load from Side X is greater than the other side. In this case, would I only need to check the shear interface between the slab and the wall (for the top wall and slab 8'5" lateral earth/surcharge force) to make sure it can transfer that sliding force to the lower walls and then consider the passive resistance of the lower wall opposite Side X against the full lateral pressure of Side X (15'5") to confirm that the whole system won't slide?

Would overturning be a problem here if the wall is effectively propped approximately mid-height?
 
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Would overturning be a problem here if the wall is effectively propped approximately mid-height?
If you excavate side Y without taking any measurement , you need to check sliding, overturning and BM check of the stem wall and moreover stability of excavation at Y side .
My suggestion would be provide shoring struts and sheeting at side Y.
 
1) Man, do I ever not feel good about shear friction at the block to slab interface.

2) Yes to overturning and sliding. I'd be inclined to imagine that whole, lower box as kind of the "footing" on a conventional retaining wall. Then design the box with a diaphragm, shear walls etc.

3) Is there something that prevents you from making the foundations a raft? I feel as though kick ass tension tying across the bottom of the walls would be great here.
 

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