New Engineer here looking for advice on his first project 1

[CEguyWSU]

So I was given the task of designing a half street improvement that will be demolished and replaced. It's only about 150' stretch. Local jurisdictions require a min. 2% cross slope from CL to gutters and a min. 0.5% flow line in the gutters. Problem is the road is flat, we are talking 0.25%-0.1% throughout the CL of the road and existing gutters. The entire length of the road is sloping in one direction.

If I hold the min 0.5% flow line along the gutter I can tie into the existing with about 3" to spare, but it does not meet the 2% cross slope of the road.

If I hold the min of the 2% cross slope of the road then the gutters end up going below the 0.5% min and I tie in the the existing 6" to high, creating a low point.

This is a small job with a low budget so there is not much else that can be done out there without killing the project. Any advice?

 

[fel3]

Sometimes you just can't get there from here. Based on your description, this seems to be such a case. This is actually quite common on retrofits and reconstructions.

When two standards are in conflict, and no other solution is available, one or both must give way. If the standards cannot be violated, then the project scope/budget may need to expand to the point where an acceptable solution can be found.

Here are a few thoughts:
(1) In addition to the information you provided, determine the slopes that would result from matching each end of the gutter, then paving from centerline to the gutter lip (e.g. maybe you get a 0.35% gutter slope and a 1.8% pavement cross-slope. Next, ask the local jurisdiction if these sub-standard slopes are acceptable. If YES, get that in writing and proceed. If NO, find out how far they are willing to bend either requirement. I have worked with agencies that require a 0.25% minimum gutter slope, but will allow as low as 0.15% on a case-by-case basis. They will also sometimes allows cross-slopes as low as 1.5% with permission.
(2) Could you solve the problem by shifting (up/down/left/right) the road crown, regrading and repaving across the centerline, or some other "out of scope" solution? If so, then maybe the scope and budget need to be modified to make this possible.

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

 

[cvg]

the reason for the minimum slopes is drainage. you need to demonstrate that poor drainage does not create an unsafe condition

 

[engineered2005]

Agree with both above posters. We refer to this as a "design exception" and it is very common with public DOT projects. Your best bet is to maximize all parameters. You should present your best solution to the client and show that you are improving on the existing conditions.

You did not indicate if there are existing drainage issues? If there are, then you need to make sure you do whatever you can to address those. As fel3 mentioned, the slopes are all required for drainage purposes. I've used 0.35% min slope in the past when 0.5% was not achievable and if you are able to obtain "approval" on that, you should be able to get close to the 2% xslope.

Brian|PA EIT|Civil-Highway Engineer
Consulting Southcentral PA
PSU 2009|BS Civil