Bearing capacity depends on the stength of the soils in the influence zone. If the loaded area is the size of a building mat, the soil conditions to some great depth may be required. If the loaded area is the size of my office the soil conditions to the depth of 20 or 40 ft may be required. If the loaded area is a few square inches, well all the stresses may be contained within the pavement structure.
Then again, maybe you are talking about the California Bearing Ratio.
you may want to use R-value rather than CBR, it seems that R-value is a bit more appropriate for "un-paved roads" whereas CBR is more appropriate for compacted paving layers.
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jjesik...don't dismiss GPT's comment. He is correct. You need the STABILITY of the roadway, not the BEARING CAPACITY of the soil. There are design procedures for unpaved roadways, none of which require a "bearing capacity". That is a foundation requirement for static loads from buildings.
You are probably looking for a stability value as determined by the California BEARING Ratio (CBR) test. This is a value that is directly used in the design of roadway structural sections whether paved or not. Also, you don't need the total load of the fire equipment as much as you need the axle distributed loads for the equipment. This is the general basis for the design.
Thanks, and yea I know what you are talking about, I have used both R and CBR values to develop cross sections for many unpaved and paved roads. I haven't dismissed GPT's comments either, I do use the axle loading for the fire trucks.
I'll stick with what I know and should have expected the responses I received.
Your sarcasm is, in my opinion, not warranted. You asked for a building foundation parameter, not a pavement parameter, yet pavement was your application.
Check with a college that has an agricultural - engineering department They may have, recommendations for gravel roads in farming usages. Another possibility is a city engineering department with a standard for unpaved roads in new subdivisions. Another might be an open pit mining company which has to have temporary roads for their work. The Federal Forest Service probably also has some standards that may satisfy.
And don't ask for bearing capacity or they won't know what you need. Ask for traffic axle load ratings. That also may require trucks per day also.
jjesik question is due to the request of the local Fire Marshall or whatever they are called in your area.
I have been asked to provide graveled driveway and private road sections for a '75,000 lb truck'. I have explained the criteria is wrong but, the Fire Marshall basically says 'My bigger trucks are 75,000 lb and The road must hold it.'
I smile, provide the various regulator (usually an engineer) what should work and have been countered with 'how do you know that will work?'. I opine that those who who can't ask proper questions may not understand when a proper answer has been provided.
Yes, proper testing & design, using common methods will work. The 75,000 lb truck criteria without the axle & tire configuration is a silly criteria. I say, Go to the firehouse and count the axles & tires.
