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Homework Help: Flexible Pavement Design Question

  1. May 13, 2007 #1
    1. The problem statement, all variables and given/known data

    Design a flexible pavement to last for 25 years. The initial PI is 4.2 and the terminal PI is 2.5. The subgrade has resilient modulus of 12,000 psi. The reliability is 95%, and the overall standard deviation is 0.4. The ADT is 25,000 light vehicles (two 2-Kip axels), 1,000 single unit trucks (one 8-Kip single axel and one 22-Kip single axel), and 500 semi-trailer trucks (one 10-Kip single axel, one 16-Kip tandem axel, and one 44-Kip triple axel). Use good drainage base and sub-base material.

    State your assumptions clearly. You need to do one iteration only even if your initial assumption(s) are not validated after solving the problem.

    2. Relevant equations


    3. The attempt at a solution

    i don't get how to get Zr in the empirical equation. i got .557 for my SN (after much algebra through that long equation to solve for SN) but when i used the nomograph (assuming SN=5) i got about 4.6 for my SN. my design came out to be:

    D1=4" D2=10" and D3=9.45" after using 4.6 as SN.
    am i doing this correctly? how do you know what coefficient to use for m2 and m3? i assumed 1, which i don't know if it that is correct to assume or not.

    i just received this problem and spent a good 2 hours or so on it; please forgive me but i need help soon!
    thanks! happy mothers day!
    Last edited by a moderator: Apr 22, 2017
  2. jcsd
  3. May 13, 2007 #2


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    Homework Helper

    Sorry, i can't help much. My knowledge on highways is upto the subgrade. I haven't designed a pavement, yet. Althought the website does reference a table for the value in an AASHTO guide, maybe that's the problem?
  4. May 13, 2007 #3
    thanks cyclovenom. i think i might just leave it at that, i followed the procedure the professor gave, so i just hope he won't have a fit.

    oh one more question, do you know how to calculate highway capacity? i'm not sure how to include a 6% grade into the factor of Level of Service and the highway capacity. thanks again!
  5. May 14, 2007 #4


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    Homework Helper

    Funny thing, i'm taking that class now!, and we just started, so i can't help you now... :rolleyes:
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