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Soil Thermal Resistivity

thread261-114324

Soil Thermal Resistivity

Soil Thermal Resistivity

(OP)
I am working on a project involving underground power cable installation.  We need to know the earth's thermal resistivity which has units of (degrees-C)(centimeter)/(Watt).  Typical values can range from 30 - 300 for most cable installations.

A company has conducted tests but the results appear to be way too high.  The results show both wet and dry conditions.  The dry numbers are between 542 and 1320, the wet numbers are between 118 and 468.  We were expecting a number somewhere between 80 and 120.

The area in question is Solano County, California.  Does anyone have experience in evaluating these numbers?

Can anyone recommend a company that does have experience for possible backup testing.

Thanks in advance!

RE: Soil Thermal Resistivity

The results are too high for thermal resistivity.
Perhaps the lab misuderstood your request and ran an electrical resistivity used to determine corrosivity instead?  The results would be in units of (ohm-cm).  
Some factors that will determine thermal resistivity of a soil are:
1.Dry Density- Lower Density=More Air Pores when dry=higher thermal resistivity
2.Water Content- Water~165(degrees-C-cm/Watt) and Air~4500 (degrees-C-cm/Watt)
3.Mineral Type and Soil Composition - Organics up to 500 (degrees-C-cm/Watt) dry
For backup tesing try soilengineeringtesting.com
Good Luck

RE: Soil Thermal Resistivity

(OP)
After talking with other experts, they seem to agree that something is seriously wrong with the numbers.

We are working on hiring Geotherm Inc. to perform backup testing.

RE: Soil Thermal Resistivity

I am having the same difficulty finding a good soil as well as a testing facility (near Tulsa, OK).  Does anyone have contact information on Geotherm Inc.?

RE: Soil Thermal Resistivity

(OP)
Their website is at http://neptune.on.ca/~geotherm/index2.htm
Ask for Deepak.  

We just got back a copy of the test results.  The numbers were more realistic than the first set of results (80 to 150 depending on the location).

I would recommend them.  This is their specialty, JMO.

RE: Soil Thermal Resistivity

Thanks for the information

RE: Soil Thermal Resistivity

I am looking for a spec for a corrective thermal backfill, a well-graded mixture of sand I am thinking, does anyone know of or have such a spec (simple gradation spec)?

Thanks much

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