Have a set of plans. Ditch cross-section detail states 4:1 min slope (varies).
Plans illustrate a 10’ wide ditch and has specific grade breaks at centerline, with corresponding elevations at the hinge. Differences in cl to hinge are are 2.5’ deep for some. But only 2.0’ (5:1) and 1.5’ (6.666:1) on others, while some are only 1.0’ deep (10:1).
The plans say 4:1 minimum. Minimum meaning that it should be that or steeper.
Yet the design numbers at cl and hinge indicate the 4:1 as a maximum, and sides flatter across the 10 feet on most slopes.
Is it a mistake in the MIN usage, when they mean MAX, or is this sinus headache causing a mind-fog.
If you have to ask, get it clarified.
Sounds to me like it's time for the infamous "RFI" from the designer.
I wish I could ask!
But the designer is not responding to any design questions, because they performed the design over 3 years ago, and no longer have a contract to charge against for revisions. But that's another story.
So to clarify, should it be MAX 4:1 and flatter...
4:1 Min. (varies) means that is as steep as the slope should be and can be a flatter slope, i.e., 5:1 - 6:1 - 10:1 - 12:1, etc.
I design ditches and other Civil works daily. When I read your original post I automatically assumed that 4:1 minimum means that all slopes must be 4H to 1V or flatter. Looking at the examples you provided that seems to make sense.
> 4:1 Min. (varies) means that is as steep as the slope should be and can be a flatter slope, i.e., 5:1 - 6:1 - 10:1 - 12:1, etc.
Logic says you are right... but would a minimum pipe slope also be 1:200 or Flatter?
Then you can RFI the owner! Just let them know you need verification on the design data before you can start. (Cheapskates!)
Probably a simple typo. I would think the designer/drafter is usually describing minimum slopes for gutters, pads, pipes, etc... clearly something that needs to drain. I am sure that Max is intended, but a CYA is in order, if not from the designer then the owner and the controlling agency.
Peter,
Dirt one way, pipes another, crazy business we are in!:'(
1:200 would be 0.5%, which is not that unusual for large culvert or sewer trunk lines. I've seen some really large sewer runs that are less than 0.1% - which is a complete PITA for layout.
Perhaps the design firm needs a call from its BTR...?
Peter,
The 4:1 is the side slope. You are talking about the slope of the flow. Two completely different things.
In reference to the original question, 4:1 is good. 6:1 is good. 10:1 is good. Anything flatter than a 12:1 may cause drainage problems. Anything 3:1 or steeper would be dangerous if someone ran off the road and require guardrail if it is very deep.
It should have been labeled 4:1max.
James
Yes, I was referencing the slope as being the side slope.
MAX is what I was thinking...
Then make the owner make the decision. Or tell the designer there seems to be a mistake in his plans. Don't take on liability you are not going to get paid for and that is out of your scope of work.
i had to look it up
a 21" diameter pipe can be laid at 0.1%. anything lager can be flatter and still meet the 2 ft/sec minimum.
man, it seems too flat to work. those crazy engineers... what will they think of next?
4:1 Minimum
4 is the minimum number. 5 is greater than 4, so a flatter side slope is acceptable.
4:1 is Run to Rise.
1/4 is Rise over Run. Preferrable method of reference.
Roof slopes are defined in pitch, i.e. 1/4, 3/12, 4/12, 5/12
Many codes and ordinances do not get it right.
On any of my design plans I include a sketch to clarify the intent.
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Paul in PA
4:1 Minimum
4H:1V
