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I was drawing up a plan to create a connection between two ponds using cinder block walls to create a wide chute and weir boards to control the water levels. (Think of an Agri-Drain box control structure that is 4' wide.)
However, the concrete footings must be on clay (instead of the normal gravel-packed base) because I do NOT want subsurface water flows between the two ponds when one is drawn down.
Clay is considered a weak soil and is also problematic due to swelling and shrinking during wet/dry cycles. I do not think the latter will be a problem because this clay should always remain moist from at least one of the ponds. I am worried about the clay "weakness".
This clay visibly looks like it is perfectly sealed since it is very dense and has zero plant roots. However, when I excavate below the groundwater level, it will weep tiny amounts of water - so it is not perfectly compacted.
I will compact some more prior to pouring concrete. I am also expanding the footing from the recommended 16" wide to 24" wide. Finally, I am going to add rigid supports connecting the two walls. Basically, as one wall tries to push "in", it will be opposed by the other wall trying to push "in" in the opposite direction.
Question:
These two cinder block walls will have a dirt/clay berm piled to the "outside" of each. The forces will be essentially the same as those on a 6' high retaining wall.
Can this work with a concrete footing on clay, or will the footings shift enough that the mortar in the cinder block joints will fail?
Thanks, FishinRod
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