Flexible Pavement Design Question

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Discussion Overview

The discussion revolves around a homework problem related to the design of a flexible pavement intended to last for 25 years, incorporating various parameters such as initial and terminal performance indices, resilient modulus, reliability, and traffic data. Participants seek assistance with specific calculations and assumptions involved in the design process.

Discussion Character

  • Homework-related
  • Technical explanation

Main Points Raised

  • One participant expresses confusion regarding the calculation of Zr in the empirical equation and notes a discrepancy in their calculated Structural Number (SN) compared to a nomograph.
  • The same participant mentions assumptions made regarding coefficients m2 and m3, questioning their validity.
  • Another participant indicates a lack of experience in pavement design and suggests consulting an AASHTO guide for relevant tables.
  • There are inquiries about calculating highway capacity, specifically how to factor in a 6% grade into Level of Service and highway capacity calculations.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the correct approach to the problem, and multiple viewpoints regarding the assumptions and calculations remain unresolved.

Contextual Notes

Participants express uncertainty about the appropriateness of their assumptions and calculations, particularly regarding coefficients and empirical equations. The discussion reflects a reliance on specific guidelines and resources that may not be fully addressed.

Who May Find This Useful

Students studying civil engineering or related fields, particularly those focusing on pavement design and highway capacity analysis.

mrmotobiker
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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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