Flexible Pavement Design Question

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The discussion revolves around designing a flexible pavement with specified parameters for a 25-year lifespan, including initial and terminal performance indices, resilient modulus, and traffic data. A participant expresses confusion about calculating the structural number (SN) and the appropriate coefficients for layers in the pavement design. They report an SN calculation of 4.6 using a nomograph, which differs from their algebraic result of 5. Additionally, there are inquiries about calculating highway capacity, particularly how to factor in a 6% grade for Level of Service. The conversation highlights the challenges faced by students in applying theoretical knowledge to practical design problems.
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Homework Statement



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.

Homework Equations



http://training.ce.washington.edu/WSDOT/Modules/06_structural_design/06-3_body.htm

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!
 
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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?
 
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!
 
mrmotobiker said:
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!


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

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