Cantilevered wall retaining water 3

[DenverStruct]

Lets say you have an L shaped retaining wall that is buried around 3 ft and stick out of the ground about 10 ft. Can you count on the weight of the water above the heel to resist the load? I do not think I can, can't I? Worst case, water will fill up to the top of the wall.

 

[BridgeSmith]

Motorcity, I just wanted to be sure that it was understood that the weight of the water can be counted for resistance ONLY if there is a waterproof barrier above the footing. Otherwise, it's no different than a concrete block submerged in a pool, with no resistance except the net weight of the concrete.

 

[Guest262653]

Probably considering the net weight of the concrete is a bit too conservative. Like I mentioned previously, if we consider a toe drain, it's plausible to assume a linear variation of the uplift water pressure from the maximum pressure at the heel to zero (or close) at the wall's toe. If a uniform uplift pressure diagram was considered at the bottom of the footing, there would probably be an horizontal water load at the outer face and we'd be talking of stable wall fully embedded in water.

 

[BridgeSmith]

"Like I mentioned previously, if we consider a toe drain, it's plausible to assume a linear variation of the uplift water pressure from the maximum pressure at the heel to zero (or close) at the wall's toe."

If you had a a toe drain that you could count on, there could be some assumptions you could make about the water pressure distribution on the footing based on the permeability of the foundation soil. However, if I understand the case under consideration correctly, the structure's purpose is to contain contaminated water. Having a toe drain would defeat that purpose.

 

[Guest262653]

Sorry. I somehow missed the contaminated water reference. In that case, shouldn't a ground slab be used to avoid soil contamination?

 

[BridgeSmith]

Yes, I would think a slab or waterproof barrier of some kind would be necessary, both to protect the soil and to avoid having to consider the submerged footing condition, which would negate most of the resisting weight. Perhaps I should have quoted DenverStruct's statement from yesterday in my response:

"It is exactly like avscorrie's drawing except it does not have a slab. The L shape is just buried down 3 ft with just soil. No concrete slab on the finished grade."

I was just saying the slab at finished grade, or some other means of keeping the liquid on top of the backfill and footing, is a key element. Without it, you only have the resistance of 87 pcf for the concrete heel and less than that for the soil on top of the heel.

Depending on the possible failure modes of the primary containment tank, dynamic water pressures may have to be considered, also.

 

[Guest262653]

I totally agree with you. The waterproofing slab is a key element to make this solution feasible and economic. Additionally, the seepage under the foundation, besides allowing soil contamination and introducing uplift pressures and reduced adhesion, may also lead to soil piping if not accounted for properly.