Flexible Pavement Design Question

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In summary, the homework statement is that a flexible pavement should last for 25 years. The initial PI is 4.2 and the terminal PI is 2.5. The subgrade has a 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).
  • #1
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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  • #2
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?
 
  • #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!
 
  • #4
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:
 

FAQ: Flexible Pavement Design Question

What is flexible pavement design?

Flexible pavement design is a process used to determine the appropriate thickness and composition of layers for a road or pavement to ensure proper support and longevity under traffic and environmental conditions.

What factors are considered in flexible pavement design?

There are several factors that are considered in flexible pavement design, including traffic volume, soil properties, climate conditions, and expected service life of the pavement. Other factors may include cost, availability of materials, and environmental concerns.

What are the different layers in a flexible pavement design?

A typical flexible pavement design consists of three main layers: the subgrade, base course, and surface course. The subgrade is the natural soil or compacted fill that provides the foundation for the pavement. The base course is a layer of crushed stone or gravel that provides additional support and helps distribute the load from traffic. The surface course is the top layer of the pavement, usually made of asphalt or concrete, that provides a smooth and durable driving surface.

How is the thickness of each layer determined in flexible pavement design?

The thickness of each layer in flexible pavement design is determined by considering the traffic load, soil properties, and climate conditions. Various methods, such as the American Association of State Highway and Transportation Officials (AASHTO) design method, are used to calculate the required thickness for each layer to ensure the pavement can withstand the expected traffic and environmental conditions.

How does flexible pavement design differ from rigid pavement design?

Flexible pavement design differs from rigid pavement design in terms of the materials used and the behavior under traffic load. Flexible pavements use materials such as asphalt or bitumen, which are more flexible and can bend under heavy loads, while rigid pavements use materials such as concrete, which are more rigid and can crack under heavy loads. Additionally, the design process and factors considered may differ between the two types of pavements.

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