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Concrete "Void" area inside a lift station

Concrete "Void" area inside a lift station

Concrete "Void" area inside a lift station

(OP)
Hello-

Does anyone have any advice on what to do with a 'void' area that we have in a lift station. The lift station base slab is 34ft deep, and a pump will be installed at this base level.

Above the base is a 6ft high "shelf" that needs to be built up. The current set of drawings show this as being solid concrete, which seems wasteful to me since the interior diameter of the well is 18ft.

I was thinking we could cast a wall on site, then fill the 'void' area with stabilized sand (or other material). Then pour a 6" slab on top. I don't know how easy it would be to get stabilized sand to the bottom of a 34ft hole, so maybe this is not practical.

We have done these before and just made the whole platform out of 2000psi 'lean concrete', but the project dimensions were much smaller so it was not as wasteful.

See below.... what do you think? I"m open to input.

RE: Concrete "Void" area inside a lift station

Suggest using solid concrete. I would not want to "fiddle" around forming (placing & curing walls), then backfilling with sand, then forming (placing & curing) a cap on the sand... just to "try" to save some money. All these outlined steps take extra time and time is money. Bulk concrete is not that expensive (per cubic yard).

Also, in the USA the structure is almost certainly a confined space, per OSHA. Use concrete and get out of that pit. Select the concrete mix carefully... to low a strength and it will take "forever" to get to design strength. Too high a strength and heat of hydration for the six foot thick concrete could be an issue. Want a mix that has high early strength, too. With some forethought, an optimum concrete mix design can be selected.

www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

RE: Concrete "Void" area inside a lift station

Agree with SlideRuleEra. Messing around with sand, CLSM, boulders, (yes, I've had that suggested) or earth is not worth it. Yes, you'll have a mass concrete pour, but you don't have to worry about the sand space leaking and getting all septic. And no matter what anyone tells you, concrete used in this way is just the off the truck cost ($100 to $125 a cu. yd.) with no finishing and minimal reinforcing. And the weight might come in handy vs. flotation.

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