How to calculate ground temperature from ambient temperature? 1

[saadicarnot]

Is there any methodology by which one can calculate ground temperature from air/ambient temperature? I want to calculate de-rating factors for cable current carrying capacity but the project specifications don’t give any information about ground temperature.

 

[escrowe]

Yes. Is this for soil beneath a climate-controlled structure?
With soil data, particularly grain size and moisture content, an estimate is possible.
Also, see tips dealing with thermodynamics in other threads.

 

[CarlB]

The ground temperature fluctuates seasonally, like the surface temperature. The fluctuation amount decreases with depth, to a negligible amount at about 30 feet. The extremes lag the surface times by weeks to months. The envelope of the extremes is the "trumpet curve".

See these technical documents:

http://irc.nrc-cnrc.gc.ca/pubs/cbd/cbd180_e.html

http://soilphysics.okstate.edu/software/SoilTemperature/document.pdf

 

[saadicarnot]

Dear escrowe. I have taken the civil boring data from project managment and I am only concerned for 1.2m depth. As you have mentioned that it is possible to have an estimate by having information of grain size and moisture content, so can you refer to some reference material? Thanks.

CarlB, your post was very helpful as I don’t have a civil background. Thanks a lot.

 

[CarlB]

Some info on thermal properties vs percent clay was included in the second website noted above. With thermal conductivity(k) & specific heat(C), you can derive the diffusivity, alpha = k/C, this is all the soil info you need to plug into the ground temperature models.

More soil properties (for granular & fine-grained) can be found at

http://training.ce.washington.edu/wsdot/modules/04_design_parameters/frost_terminology.htm

 

[saadicarnot]

Thanks a lot CarlB. It was very helpful. Thanks.