Sanitary Manhole 'Plumbness' Tolerance?

[MarshfieldTimC]

I have an 8-foot deep sanitary manhole that was installed by a contractor that was unfortunately installed out-of-plumb. I am unable to find any standards or tolerances for manhole 'plumbness'. Does anyone know how far out-of-plumb is too much for a manhole? Thanks in advance for replies.

 

[AgMechEngr]

Unfortunately, I don't know of any tolerance for plumbness for manholes post installation. The utility departments here state "must be plumb" with no deviation. How much out-of-plumb?

You are not terribly deep, which is good. I would not be too concerned about it as long as the drop across the manhole is maintained and the ladder is safe to use.

 

[MarshfieldTimC]

Contractor measured 6-inches (top to bottom), but I need to confirm this measurement.

 

[AgMechEngr]

That is unacceptable.

 

[MarshfieldTimC]

I agree that this is unacceptable, but I don't have any basis for this, aside from 'Engineering judgement'.

 

[AgMechEngr]

ACI 117-10 gives 1"/10ft for cooling towers and chimneys, but with something like this, the argument is more workmanship than function.

 

[bimr]

If you don't have it in your specifications, you may be out of luck.

Here is a typical standard specification:

F. Pipeline Sags
1. Measurement of sags in gravity sewers shall be by CCTV inspection. For new underground sewer installations, the maximum operational tolerance for sag shall be 1/2” or as specified in the Contract Documents. A calibrated 1/4” diameter steel bar/”sag gage” or approved equal device, mounted in front of the camera, shall be used to measure the depth of sag.

B. The Contractor shall furnish the original and four copies of each survey. An interpretation of each survey, together with recommendations, shall also be furnished. Horizontal deviation from plumb shall not exceed 6 inches per each 100 feet.

That is .5%.

Definition of Plumb:

What Is Plumb?
In construction or carpentry, the term plumb refers to a line or feature that is perfectly vertical. In technical design, it represents an imaginary line that runs straight to the center of the earth. Plumb is the counterpart to level, which means to be perfectly horizontal.

 

[AgMechEngr]

Depending on the orientation of the manhole and the influent/effluent, you could make the argument that the invert channel is now violating a drop across the manhole requirement. The minimum drop across manholes here is 0.2 ft. The attached drawing shows the worst-case scenario, and it is to scale. The intended drop across the manhole is shown as 0.2 ft, but with the installation it actually reversed grade to a +0.5 in.

 

[MarshfieldTimC]

Thanks to all for the great comments and ideas. Your time and contribution is appreciated!