Design of Asphalt Pavement without Subbase

[Blackfairy]

Hi, I am looking online and cannot find an answer or direction. I am from California and use Caltrans Road Design. How do I design a pavement without a subbase? I am designing an access road that will really only have at most 2-3 HS-10 trucks on it daily. My coworker said with that low traffic I can just forgo the subbase, but I cannot find a way to design it. Do I just design it as it has HMA, Base, Subbase, get thickness of each and just eliminate the subbase in the end?

I know it will depend on the subgrade but I will still have to get soil samples. Another question is how to determine if it is strong enough? Get California R value? i doubt it will be as strong as a subbase R value. I know they need to be well compacted and draining too. Get California Bearing Ratio (CBR) i guess. Though I am new and still needs to learn how to utilize it.

 

[dik]

The subbase is part of the asphalt pavement system and contributes to the strength. Without it (I'm not sure you can) you would require a greater thickness in asphalt at a greater cost. I don't design asphalt pavements.

 

[jhnblgr]

money in the subbase is best unless the existing material is gravel or stone to start with. A poor subbase will result in long term maintenance issues. Asphalt is prone to ruts, really should be seen as a wearing surface.

 

[IRstuff]

Seems like a dubious proposition; even roads with subbases get pretty beat up with heavy vehicle traffic.

One can simply compare the right lane vs. left lane on I5 in the Central Valley to see the difference in what heavy trucks do to a fully compliant roadway.

 

[fel3]

If the traffic volumes are small and/or the native soils are good, then there is no reason to use a subbase layer. AC + AB will be more than strong enough. In fact, Caltrans has an option for AC only designs. This is all covered in the Caltrans Highway Design Manual Chapter 630, Flexible Pavement. If you look at the equation for Gravel Equvalent, GE = 0.0032 x TI x (100-R), please note that R is the R-value for the layer below the layer for which the GE is being calculated. So AB on native is just as valid as AB on ASB on native. Give me a few minutes and I will post some calculation tools that I have developed for designing HMA pavements per the Caltrans Method.

 

[fel3]

Here are a couple of calculation tools that I developed for AC pavement design per the Caltrans Method. I have included an Excel spreadsheet template, a Mathcad Prime 9.0 worksheet template, and a .pdf printout of the Mathcad worksheet in case you don't have Mathcad. I first built the spreadsheet in 1987 using SuperCalc 4 (!), then later ported it to Excel. I first built the Mathcad worksheet in about 2015 using Mathcad Prime 3.0. I built both documents mostly on my own time and before joining my current employer, so they are mine to share. You are free to use them once you have satisfied yourself that they work as intended and you are free to modify them as you see fit. Neither document has any warranty or guarantee, explicit or implied.

Unless you use Mathcad, you will probably find that the Excel spreadsheet template is more useful. However, I suggest that you read through the Mathcad worksheet because it is much more heavily annotated. Please let me know if you have any questions.

 

[Blackfairy]

Here are a couple of calculation tools that I developed for AC pavement design per the Caltrans Method. I have included an Excel spreadsheet template, a Mathcad Prime 9.0 worksheet template, and a .pdf printout of the Mathcad worksheet in case you don't have Mathcad. I first built the spreadsheet in 1987 using SuperCalc 4 (!), then later ported it to Excel. I first built the Mathcad worksheet in about 2015 using Mathcad Prime 3.0. I built both documents mostly on my own time and before joining my current employer, so they are mine to share. You are free to use them once you have satisfied yourself that they work as intended and you are free to modify them as you see fit. Neither document has any warranty or guarantee, explicit or implied.

Unless you use Mathcad, you will probably find that the Excel spreadsheet template is more useful. However, I suggest that you read through the Mathcad worksheet because it is much more heavily annotated. Please let me know if you have any questions.

Thank you! this is exactly what I need. I will let you know if I have any questions but so far looking at studying the spreadsheet and comparing to what I have, it is pretty close. I just haven't found the steps to take if I want to eliminate the subbase. I will study the pdf given too as I do not have Mathcad so I have more understanding on the topic.

 

[fel3]

To eliminate AS in the spreadsheet, just enter an R-value of 0 (zero) in cell B6. If you want to eliminate AB, enter a zero in cell B5. (I need to add more instructions to the spreadsheet, that's for sure.)