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.
Now is the time for all good men to come to the aid of their country. Typing class 9th grade!
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!:'(
Now is the time for all good men to come to the aid of their country. Typing class 9th grade!
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