# Bearing Capacity of Soil from SPT test



## ckw (May 12, 2008)

Is there any way of determining the bearing capacity of soil based just on the n-values from a spt test? Or do I need more tests done?


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## Guest (May 12, 2008)

^^^ The SPT test can be used to determine bearing capacity but there is more information needed to determine the appropriateness of the SPT data towards your specific design need.

A really big question is whether or not we are discussing a shallow foundation or a deep foundation. Then there are some deviations depending on the heterogeneity of the underlying strata and contemplation of the material - mostly sands, clays, or silts?

So, what I am getting at - it takes more information and some judgement based on the end result of the data (_e.g._ purpose of the numbers relative to design) in order to say good idea or not.

If you have a more specific question, please feel free to post or PM me. I am not a bearing capacity guru but I can certainly pass along to others who are more informed than myself. 

JR


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## ckw (May 12, 2008)

jregieng said:


> ^^^ The SPT test can be used to determine bearing capacity but there is more information needed to determine the appropriateness of the SPT data towards your specific design need.
> A really big question is whether or not we are discussing a shallow foundation or a deep foundation. Then there are some deviations depending on the heterogeneity of the underlying strata and contemplation of the material - mostly sands, clays, or silts?
> 
> So, what I am getting at - it takes more information and some judgement based on the end result of the data (_e.g._ purpose of the numbers relative to design) in order to say good idea or not.
> ...



Thanks for answering.

This is for a road that will have minimal traffic for 32,000 lbs truck. It is mostly limerock. We need to determine if the subbase has the capacity to hold that type of vehicle. Right now there is 6' of subbase. Based on the test results we got, it seems fine, but of course the company needs numbers and formulas and such..... any help is greatly appreciated.

Thanks.


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## caneriver (Jul 1, 2008)

Could someone elaborate on this? How do you apply the n-value when estimating bearing pressure?

What if you have a stiff clay(cohesive material) with a shallow mat foundation and water table below the influence line?


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## moha (Oct 17, 2008)

caneriver said:


> Could someone elaborate on this? How do you apply the n-value when estimating bearing pressure? What if you have a stiff clay(cohesive material) with a shallow mat foundation and water table below the influence line?



2


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## JRCE79 (Oct 27, 2008)

ckw said:


> Thanks for answering.This is for a road that will have minimal traffic for 32,000 lbs truck. It is mostly limerock. We need to determine if the subbase has the capacity to hold that type of vehicle. Right now there is 6' of subbase. Based on the test results we got, it seems fine, but of course the company needs numbers and formulas and such..... any help is greatly appreciated.
> 
> Thanks.



Usually there's charts to help you with this. A good book is the Asphalt Handbook.

http://www.asphaltinstitute.org/store_prod...asp?inve_id=443

Besides doing a SPT you should have the testing lab get a bulk sample and perform an unsoaked CBR test to determine the CBR value of the subgrade. From there you should be able to calculate if the existing pavement composition is sufficient to handle the traffic.


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## NovoTech (Jul 9, 2009)

Hi

this website has FREE software to calculate bearing capacity of soil and even liquefaction from SPT blow counts N60 numbers.

http://www.novotechsoftware.com/SPT/Index.html


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