Desnity of liquid contained in a sewage treatment plant? 4

[Tstruct]

I am performing structural design of a sewage treatment plant. As far as I have found on internet the liquid (sludge or whatever) present in a sewage treatment plant at any stage of the whole process has density around 70 lb/ft3. I need input of structural engineers who have already performed such design. Is this value of the liquid correct? Also please guide, what does ACI say about shear limit for propped retaining walls (slab on top)? Can I allow ultimate shear up to phi Vc or should keep it below half of phi Vc?

 

[rb1957]

normal water is about 62 lb/ft3, so 70 lb/ft3 could account for "sludge and whatever" ... and why would you doubt what the internet tells you ? (smile)

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[Tstruct]

Because 70lb/ft3 feels lighter, I have no experience of sewage so need to confirm it.

 

[JStephen]

That should be something you get from the people doing the functional design, not from the internet.

 

[JoelTXCive]

I can't find it cited anywhere, but my understanding is that the unit weight of the sludge is very close to the unit weight of water. I think it's something like 65pcf versus water's 62.4pcf.

I think that 70pcf would be a conservative number.

I've done several WWTP designs in the last 6-7 years; and we do not account for a separate sludge weight. Nothing has fallen down yet.

Also, is your tank above ground or embedded in the ground? If embedded, then the controlling loading is usually the in-situ earth pressures; which are significantly more than water or sludge.

 

[HTURKAK]

My points are ;

-The following unit weights suggested at (Design of Liquid Retaining Concrete Structures (by J.P. Forth, A.J. Martin )

Water= 10.0 kN/m3

Raw sewage= 11.0 kN/m3

Digested sludge aerobic= 10.4 kN/m3

Digested sludge anaerobic= 11.3 kN/m3

Sludge from vacuum filters= 12.0 kN/m3


- The max. unit wt is for Sludge from vacuum filters and 12.0 kN/m3.
You may perform structural design assuming density 62 lb/ft3 ( except sludge tank), provided that the maximum level of the liquid would be the height of the tank/ overflow weir and the appropriate load factor is used . The load factor will compansate the density variation.


My opinion



I cannot give you the formula for success, but I can give you the formula for failure..It is: Try to please everybody.

 

[Tstruct]

@JoelTXCive
Thank you for your useful feedback. It is a sewage treatment plant within a basement, some external walls are in contact with soil. Some are internal walls having nothing on the other side. I needed density for these internal walls.

@HTURKAK
Thank you very much, I really needed some book reference too.