Designing gravel road for fire engine loads

[ckissick]

The fire chief wants me to prove that a gravel ranch road is adequate to support a 75,000 lb fire truck. Being a ranch road, traffic is very light. There will just be the occasional, if ever, instance of a fire truck driving by.

Normally, I use EAL, TI, etc., along with R-values to design a pavement section. But this seems more of a bearing capacity problem to me. What's the usual procedure here? How do you distribute the 75,000 lb to point loads per tire?

 

[fel3]

It's been a few years since I've looked into gravel road design and at the moment I can't put my fingers on the information I found back then. However, I do remember doing some Google searches for "gravel road design" and other phrases and finding that some state highway agenecies actually include design standards for gravel roads (IIRC, Alaska and North Dakota are two of them). In addition, I suspect the US Army has info that can be downloaded. I wish I could be more specific, but you may want to try some internet searches and see what pops up.

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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[civilman72]

Below is a link to the AASHTO Design of Pavement Structures - Low-Volume Road Design that contains aggregate surface design.

One thing to consider is that gravel surfaces will deteriorate, so while you may want to appease the fire department requirements now, it's just as important to remind your client that resurfacing the driveway will be important. The last thing you want to do is design something that may not work as intended (say in 15 years) when a fire truck actually needs to use it.

 

[ACtrafficengr]

One thing to kweep in mind is a good aggregate for a gravel road is a bad subbase for a paved road, and vise versa. The NY LTAP center talked NYSDOT into adding gravel road aggregate to the Standard Specs:

http://www.clrp.cornell.edu/techassistance/Gravel pdfs/material specification.pdf