Design for a structural section for asphalt pad in desert

[cher122976]

What is the best way to go about designing a structural section for an asphalt pad in desert conditions for a staging area for equipment?
We have a good subbase as soils are sand. Design will need to conform to H20 loading. There will be some heavy process equipment located on the pad so we could have point loads on asphalt from equipment stands. Heavy tractor trailers will utilize the site. The site will only be in use for 6-7 months.

 

[CPENG78]

Cher,
I would start by asking how heavy is the equipment that will use this pad and their frequency. Also, corect if I'm wrong but it sounds like the point loads will be there for a while. You may find out that H20 wheel loads may be lower that the actual equipment making use of it. As an example, I had to design a steel cover for a concrete vault which was directly on a travel lane for a parking lot. The original design met H20 loads but the fire department came back requesting that we analyze a different loading scenario that more closely resembles their equipment. As you can imagine upgrades had to be made in order to meet both the H20 loads and the Fire Department Loads.

 

[fattdad]

Special care must be made in specifying the emulsion used in the asphalt. You'll likely need a higher-than-normal performance grade to handle the static point loads and the direct heat. Learn more about Superpave and Performance Grade emulsions.

I guess you don't have to use soaked CBR values, though. . .

f-d

¡papá gordo ain’t no madre flaca!

 

[cher122976]

There are no unknowns on the project. We know the exact machinery, the weight of the machinery (6500lbs max), the length of time machinery will be on-site (9-12 months), and the soils are desert conditions, ie sand. I am trying to inquire on what is the best way to design the structural section of this pad. Off the top of my head I am thinking a 2" asphalt over 12" rock base would be adequate, but need to analytically confirm this. Since its just a pad for proccess equipment traffic volume is minimal.

 

[Ron]

cher122976...your proposed section is good; however, you need to look at the stability of the sections. The rock must be a graded aggregate base or have cement stabilization (soil-cement). The underlying sands should be stabilized and if you do so, you can reduce the thickness of the base.

I would not use an emulsion at the surface...you can use it for stabilizing base and/or subgrade. Look at a penetration resistant grade of asphalt cement for the asphalt and a dense mix with a low asphalt content. If you use a mix that requires a lot of asphalt, it will likely exhibit "tenderness" including depressions from static point loads, shearing from power steering, and shoving from repetitive stop points. The larger the coarse aggregate in the mix, the lower the asphalt content will need to be.

 

[MiketheEngineer]

If the use is so short term and loads so low - why even pave it?? Just run a bulldozer over it every few months and level it - if even needed.

 

[cher122976]

Thanks for the replies. Pad needs to be paved as forklifts will be utilizing it. Rock base course will follow very closely to ODOT standards. We dont have a geotech on this project whom normally calcs the section so just trying to determine how to calc a section for this instance.

 

[Ron]

cher122976...go to the US Army Corp of Engineers site and download their pavement design program....this should be sufficient for your purposes.

 

[cher122976]

Does ACOE have this program available? Anyone else know of any good flexible pavement design programs?

 

[Ron]

Here's a link to the USACE website for transportation. You might have to look around a bit, but they have flexible and rigid pavement design programs available for free download, for both airfields and roadways. They also have some equipment data, but you can usually find that in a variety of places.

https://transportation.wes.army.mil/pcase/

You can also use the AASHTO pavement design manual. The procedure is not difficult, but if you've never done it before, there are quite a few considerations and steps, so be careful. The AASHTO software is too expensive to use for one-time design.

 

[dicksewerrat]

I'd use Roller compacted Concrete for the pad.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[cher122976]

Is that link for USACE a viable website? Link does not work and its a hard site to find by google.

 

[cher122976]

Got it to work, thanks!

 

[diggerman]

Ron/Cher122976-

Why design for a graded aggregate base when you are miles away from any L/R quarry? Substitute the base with thicker asphalt i.e black base. You'll save money by simply adding 8 to 12 inches of Asphalt in lou of an aggregate base. To add,you said max load is only 6500lbs that seems very light for a tractor trailer. Design with 2 lifts. 1st lift black base. Let cure for approx. 28 days, tack and pave with a good friction course. Put some nice striping on it where ever you please. Done.

 

[BigH]

My suggestion is to dig out, say 2 to 3 ft of the sand, compact the base, and then replace with the sand using, say, 4% cement (or pozzalan cement) added in 8 inch lifts. This will give you a good base to work on. You might not then require an aggregate base. May want to thicken the HMA a bit - say to 3 inches or so. As for the graded aggregate base - if you have to go so far for good aggregate - where are you getting the aggregate for the 8 to 12 inches of HMA? If the sand is clean, make use of it by stabilizing as Ron earlier suggested - I've just suggested using a much deeper stabilization.
As for the asphalt - penetration grade is okay - but I would suggest a 40-50 rather than a 60-70 or 80-100 which might be suggested - but definitely would not go with 80-100 (AASHTO uses 85-100 but you will find in Asia that they make 80-100). This should prevent a problem with flushing/bleeding. Else, you could modify the asphalt with crumb rubber or polymers. We had better luck with polymers in India.