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elogp (Geotechnical)
15 Jun 09 19:04
I am designing a cement-treated base (CTB) using the PCA design guidelines for a pavement over soft ground.  The subgade will be a silty soil.  I was asked by the PM if my design included AASHTO H-25 loading and now I understand it has to do with how axle loads are transferred to drainage structures (culverts?).  The road is rural and most of the heavy traffic is 56,000 pound 4-axle gravel dumptrucks with a tandem axle (the fourth axle is retractable).

The PCA design procedure uses the fatigue factor to estimate CTB thickness.  Does the AASHTO H-25 load diagram apply to the fatigue factor calculation?  

   
jdonville (Geotechnical)
15 Jul 09 12:43
The AASHTO H-25 loading is a fictitious theoretical design truck.

Here is a primer on AASHTO pavement design that hopefully will help:

http://training.ce.washington.edu/wsdot/

Many other resources are also available online. Google "AASHTO pavement design"

Jeff
 
Dinosaur (Structural)
16 Jul 09 15:11
In bridge design we normally use HS-20 loading, and if we were asked to use HS-25 loading we would have a corresponding increase in the fatigue distress.  You may need to increase your fatigue values by 25% in this case.
ACtrafficengr (Civil/Environmental)
16 Jul 09 15:54
Since you are looking at a pavemet, not a structure, you may have better luck looking at ESALS, not H-loading.

How many ESALS per HS-25?

     "...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928

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