Model showing odd results for CTB under rigid...?

9 weeks ago by
HI everyone,

I'm trying to model the creation of a new truck lane in a heavy trafficked interstate. Existing adjacent lanes are 9" new CRCP over a thin asphalt layer over 8" of existing CRCP. I want to model a similar stiff pavement design by modeling 9" CRCP over the same thin asphalt layer (2" PG64-22) over a cement treated base comparable to the CRCP (maybe MR= 1 million.)

I see information in the 2015 guide that says the models for CTB weren't vetted by the NCHRP reports and shouldn't be used. I have also tried just choosing a base such as gravel or A-1 and just manually modifying the MR to be about 1 million.

I run a 50-year design and the IRI and punchouts are less than 10 for a good 25-30 years, and then they shoot up into the unacceptable range quickly.

WEIRDLY, I've tried changing the CTB from modulus 200,000 all the way to 2,000,000 and it has very little effect! Still the failure at 25-30 years.

I just can't believe that punchouts happen so rapidly and violently after 25 years of loading.

Any suggestions on how best to model 9" CRCP/ 2" ACP / 8" CTB? Much appreciated! Thanks!

(I'm the state pavement design engineer for Oregon DOT.)
Hi Karen, which version of the software are you using?
written 9 weeks ago by Chadwick  
Hi Chadwick, I'm using 2.3.1.
written 9 weeks ago by Karen Strauss, PE  

1 Answer

9 weeks ago by
Hi Karen,

Have you looked into using the Unbonded CRCP over CRCP design option? It is under the overlay design type. Based on the structure you described it might fit well.  I just ran a quick comparison between a unbonded CRCP overlay and the way you described it and for the unbonded overlay option at 40 years the Punchouts were at 16.05 for a 90% reliability design. Using the CRCP/AC/CTB gave results similar to what you found. I used default inputs and 4000 AADTT (43 million trucks after 40 years). Let me know if you have any questions.
Hi Wouter, I haven't tried that. I'll give it a try this morning... good idea! Thank you!
written 9 weeks ago by Karen Strauss, PE  
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