Minimum Grades in Louisiana 1

[pasa4]

I have several years of site design experience and recently started working on a large site project in Louisiana, a new geographic location for me. All my experience is from States with clay and shale soils were the minimum slope is 2% on any surface. On this project the final surface is gravel and the client is saying they want the finish grade of the site to have a 1% or less slope. These are not heavily trafficked areas but see occasional passenger trucks. The in-situ soils and the fill material is all a well graded sand (AASHTO A3). Is a 1% slope a normal/acceptable minimum slope in this geographic area and/or for these type of sand soils?

 

[Ron]

In coastal plains, it is often difficult to achieve any reasonable slope. If you have no code restrictions or mandates, 1 % will work.

 

[jgailla]

In coastal Florida and Georgia, I've gone down to 0.5% in parking lots, but there will be dips and standing water.
Decent site contractors can get to 0.75% for long stretches, such as the longitudinal drive aisle of a big parking lot.
For the perpendicular slope in a parking lot, I try to use at least 1.5%.

 

[brandonbw]

On one project we had here in Los Angeles, the contractor wouldn't build the parking lot with any grades less than 2%. Keeping the project as flat as possible was the main constraint to tie into some existing buildings and driveways throughout the large property. That was not a fun fix to do in a rush as they were rough grading the site.

If the person building it can build flatter than 2% properly and you are still following locals codes, I would say go for it. Call up someone at building and safety and ask what they will allow. Or find the inspector and ask what they will sign off on.

B+W Engineering and Design
Los Angeles Civil Engineer and Structural Engineer

http://bwengr.com

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http://bwcivilengineer.com

 

[civilman72]

In a perfect world you spec a 2% minimum grade for asphalt and a 3% min. grade for gravel.

I highly doubt even the best blade-hand could maintain a 1% minimum slope on a large gravel parking lot.

It will pothole quickly, but repairs to a gravel surface are generally cheap and may be preferable to the earthwork costs generated by trying to create a 3% slope over a large area.

 

[eea]

DOT specifications for mainline curb and gutter in my area are a minimum of 0.3% (and yes that is by stringline reference). A grade man by eyeball should be able to hit 2 to 3%, but really in this world of laser grade and GPS controls do we still have to be beholden to these old tolerances?

I'm just saying, when you specify something and a Contractor then bids it, he/she has accepted that. Saying they can't achieve grade that after the fact is not acceptable. They could take a reference pass using stringline grade control on the paver and then ski off of the mat for subsequent passes. Often times it is not a case of can be it down, but can it be done with the equipment and manpower on hand?

 

[msquared48]

1% is about 1/8" per foot and is constructible, but as Ron says, may not be practical in some locations. I have always stuck with the 1% minimum, particularly in the handicap access areas of parking lots.

Mike McCann
MMC Engineering

 

[DDBPE]

Your post indicated a gravel parking lot and therefore I do not see a problem with 1% but no less. The only problem I have is gravel will move around as traffic is on it and will need to be regraded from time to time. I would suggest, if drainage is not the problem, to use a dense graded aggregate (21A or 21B in Virginia, ABC in NC) or whatever designation the Louisiana DOT has for this material, typical quarries, as ours does, produces DOT aggregates . The material can be graded and compacted and would hold up for a while and if later on the owner decides to pave the lot, the sub-base is already there and would only need dressing up.

Now for the paving comments, less than 1% is difficult, even with the electronics. We typically will not guarantee a lot will not have ponding or drainage issues if it is less than 1%, it is written into our quotes and contracts, especially in a parking lot. Typically lots will have obstacles (islands, lights, etc.) which make paving difficult, electronics for grade control work better for wide open lots, no islands, or long runs (highway and airports). Also, if the lot has curb and gutter, the tolerances on those are usually different than the paving. I have seen 1/2" on curb and gutter and 1/4" on the paving and we have to tie into the curb and gutter.

Yes sting-lines and subsequent lifts with the ski is good practice (airports require this and some DOT's), but in parking lots, it is not practical unless it is again, wide open without obstacles. Using a joint matcher is good in all cases, this creates smooth joints between passes.

One more thing, typically someone else does the grading and then has a paving contractor come in. Now in my experience, the grading contractor on parking lots has a tolerance different than the paving or they think if the grade is rough, the paving contractor can fix it. What this causes is inconsistent lift thickness, which compacts differently and therefore creates high or low areas. Compaction factors are 1/4" per inch laid typically.

 

[pasa4]

Thanks to all for sharing your knowledge.

 

[krautfed]

I know this is an old thread, but I figured I'd respond for future searchers.

1% finished grade is common for surface drainage in lower LA. Ditches and swales can be spec'ed at 0.5%. It takes hydraulic head to move water anywhere in LA so a good ditch and swale system to is key to keeping the lot dry. For parking lots, we use 12" compacted fill, a geotextile fabric, 5" of #610 stone base, 3" of #57 stone surface. For roadways with heavy trucks and equipment, we replace the above 3" of #57 stone surface with 3" of #4. It's not very fun to walk on, but it stays in place.