DogHouse Manhole - Deflection Angle 2

[tehparadox86]

I have a proposed sanitary sewer line that I need to design with a new 48" doghouse manhole. Local code stipulates that the new line must connect at exactly 90 degrees. My connection will be more than 90 degrees (see attached). Do you guys think this is too strict, especially if we have a enough slope and flow that there won't an issue with buildup? I don't want to move the manhole since I have to be within 10' of a utility easement (purple line) and don't want to mess with resizing the lots. LOL.

https://files.engineering.com/getfile.aspx?folder=65e23880-9432-42c2-a13b-e7f728b99da7&file=SS.PNG

 

[fel3]

I've been designing municipal infrastructure for 42 years and this is my first time seeing the term "doghouse manhole." I had to look it up. BTW, I have used them before, but nobody I know around here calls them "doghouse manholes."

I doubt that the local code is specifying the deflection angle at the manhole as per the title of your post. After all, manholes strung out along a straight sewer result in deflection angles of 180°.

Rather, I suspect that the local code is saying that sewers connecting to the manhole need to be perpendicular to the tangent line of the face of the manhole and cannot be offset from being radial to the center.

Perhaps my interpretation is incorrect, but that's how I see it.

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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[bridgebuster]

I agree with fel3. I've been working on infrastructure projects for 40+ years in NYC; pipes come in at all angles.

 

[tehparadox86]

Fel3, I'm a visual learner. Couldy you do a sketch?

 

[AgMechEngr]

I would bet that the code's intention is that the connection is not greater than 90 degrees, so that you don't have issues with counterflow. In the image, the configuration on the left would be permissible. The configuration on the right would be greater than 90 degrees and cause counterflow.

 

[AgMechEngr]

Also, what fel3 says makes good sense.

 

[nackra]

Other reference guides for your consideration:

https://precast.org/wp-content/uploads/2021/10/Manhole-Sizing-Recommendations-2021.pdf

https://precast.org/2012/12/anatomy-of-a-doghouse-manhole/?fs=doghouse