Sewage Lift Station Minimum Wall Thickness
Sewage Lift Station Minimum Wall Thickness
(OP)
Happy New Year All:
I am designing a sewage lift station with 28' deep walls and liquid level will be maxed out at the 22' depth level. This work is being done for a general contractor who received this task as a change order to their contract. In the drawings provided for the contractor to price the change, the wall thicknesses are shown as 10".
The utility engineers provided this drawing.
My question is: All our previous work of this type conformed with ACI 350-6 which states that the minimum thickness of any wall 10' or higher, in contact with liquid, shall be 12". The utility designer is saying that the 10" thickness is acceptable since both sides of the lift station wall (liquid side and soil side) will be thoroughly sealed and the concrete protected against the moisture.
They also state that this exception is in the code (I'm assuming ACI?) but cannot tell me where and I cannot locate it.
Has anyone out there encountered this issue?
Can anyone provide guidance?
Thanks!!
Trillers
I am designing a sewage lift station with 28' deep walls and liquid level will be maxed out at the 22' depth level. This work is being done for a general contractor who received this task as a change order to their contract. In the drawings provided for the contractor to price the change, the wall thicknesses are shown as 10".
The utility engineers provided this drawing.
My question is: All our previous work of this type conformed with ACI 350-6 which states that the minimum thickness of any wall 10' or higher, in contact with liquid, shall be 12". The utility designer is saying that the 10" thickness is acceptable since both sides of the lift station wall (liquid side and soil side) will be thoroughly sealed and the concrete protected against the moisture.
They also state that this exception is in the code (I'm assuming ACI?) but cannot tell me where and I cannot locate it.
Has anyone out there encountered this issue?
Can anyone provide guidance?
Thanks!!
Trillers





RE: Sewage Lift Station Minimum Wall Thickness
I'm not sure you're going to be able to use ACI 350 or 318 to make an ironclad case. They're more likely to hint at thicknesses than to require them. But trying to drop concrete 30 feet and vibrate it is damn near impossible. Fitting waterstops is very difficult. Even 12 inch walls are tough. It's common sense.
A lot of contractors (and owners) are really stupid about concrete thicknesses. They have to build basically the same forms and tie the same reinforcement for a 10 inch wall vs. a 12 inch wall. The only additional cost is the concrete out of the truck (about $110 a cu yd.). They'll eat up that money fixing one rock pocket, not to mention the four or five they're going to get.
RE: Sewage Lift Station Minimum Wall Thickness
http://www.concretepipe.org/wp-content/uploads/201...
RE: Sewage Lift Station Minimum Wall Thickness
I'd say start with 12 inches and add an inch for every foot depth over that.
RE: Sewage Lift Station Minimum Wall Thickness
Regardless, the document presents the formula to calculate the thickness.
RE: Sewage Lift Station Minimum Wall Thickness
RE: Sewage Lift Station Minimum Wall Thickness
So we cannot use the reduced PCA Tension force based on their tables.
We are now leaning towards designing it as a cast in place manhole but can't find any good references for analyzing the Steel stress to maintain lower concrete stresses.
We want to ensure that our tensile steel is adequate. One colleague suggested that we s imply treat the curved wall section as a series of short sections of simply supported beams.
Not sure i'm comfortable with this.
Any ideas or references to suggest?
RE: Sewage Lift Station Minimum Wall Thickness
By the way, your colleagues suggestion is wacky.
RE: Sewage Lift Station Minimum Wall Thickness
I am thinking we treat the vertical sections with bw being 12" as a cantilever...but then that gives some large moments, nonetheless I think this is the correct approach.
Your thoughts?
RE: Sewage Lift Station Minimum Wall Thickness