Gtting CBR of over 150%
Gtting CBR of over 150%
(OP)
We have got a confusing with results from CBR unsoaked.
It yields a CBR of over 150%. A materail is sandy silt compacted with modified Proctor. Even after repeating the CBR test, the results are the more or less the same. Could anybody give us any comments?
It yields a CBR of over 150%. A materail is sandy silt compacted with modified Proctor. Even after repeating the CBR test, the results are the more or less the same. Could anybody give us any comments?





RE: Gtting CBR of over 150%
The soil type is silty sand having fine grain soil of 15%.
RE: Gtting CBR of over 150%
RE: Gtting CBR of over 150%
¡papá gordo ain’t no madre flaca!
RE: Gtting CBR of over 150%
Thanks also fattdad.
RE: Gtting CBR of over 150%
f-d
¡papá gordo ain’t no madre flaca!
RE: Gtting CBR of over 150%
RE: Gtting CBR of over 150%
It is assumed that the test procedure is correct and results have been checked to ensure that corrections are made etc. This being the case, one may wish to believe that the reported result is reasonable noting as well that most of us have been calibrated with the standard Proctor CBR.
It would be of interest if the soil proposed can be compacted to modified Proctor values in the field. This may not be readily achieved. I would suggest that the CBR test be undertaken at 95 and 97% of modified density at the corresponding moistures. Life in the field is hardly ever as controlled as in the lab - not only moisture but variability of material,Contractor and Client pressures.
I also presume that this temporary road would be capped, if not then you may well be advised to undertake a soaked CBR test. On sands compacted to standard Proctor, I have noted that the CBR of the soaked sample drops to about half of the unsoaked value.
Question: The load of 200 tons how will this be distributed and what is the proposed pavement structure.
RE: Gtting CBR of over 150%
Irrespective of the appropriate design CBR value what method will you be using to convert the 200 ton vehicle weight into equivalent 18-kip axle loads? Most design methods show 18-kips equivalancies (sp) for trucks up to 40 tons (i.e., tractor-trailer combinations). What you need to identify is how the off-road tires, axle loads, etc. convert to equivalent 18-kip axle loads.
As an important asside do you plan on completing a design that is just gravel or will there be some asphalt on the surface? For my practice, I would never consider a heavy-duty asphalt pavement section thinner than 2 in surface, 3 in base and 6 in aggregate. Depending on your design life, 18-kip axle loads and anticipated life, no matter what CBR value you use this "minimum" pavement section may be adequate. For a gravel-only pavement (and considering just how big this vehicle seems to be), I'd think you'd need at least 12 to 14 inches of dense-graded aggregate.
Good luck.
f-d, p.e.
¡papá gordo ain’t no madre flaca!
RE: Gtting CBR of over 150%
RE: Gtting CBR of over 150%
I am just back from another construction site and now awaiting to see a repeated result from laboratory. Hopefully it will be available within today. The repeated result will be informed here.
RE: Gtting CBR of over 150%