×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Converting to Two Layer Soil Resistivity Model

Converting to Two Layer Soil Resistivity Model

Converting to Two Layer Soil Resistivity Model

(OP)
HI all,

I received a multi-layer soil resistivity data derived from 4 pin Wenner test method based on equal probe spacing (spacing not given) and graphical curve fitting from one area and wishes to use it as preliminary basis only. The soil resistivity values are as follows:

a. 220 ohm-meter at 1.2 meter soil thickness (1.2 meter depth below grade)
b. 175 ohm-meter at next 6 meter soil thickness (7.2 meter depth below grade)
c. 500 ohm-meter at next 20 meter soil thickness (27.2 meter depth below grade)
d. 100 ohm-meter at infinite depth below 27.2 meter depth

ETAP ground grid software uses 2-layer soil model: top and bottom soil (as per IEEE 80-2000). I would use 100 ohm-meter for the bottom soil model (item d). This leaves me to come with an equivalent top soil (not surface soil)resistivity value based on items a~c.

I. On method I am thinking of is to apply weighted percentage on each soil resistivity based on percentage depth and take the sum. Hence,

(220 x 1.2/27.2) + (175 x 6/27.2) + (500 x 20/27.2) = 415.96 Ohm-meter for soil thickness of 27.2 meters

II. Another method is to simply get the average of items a-c disregarding their different depths. Hence,
(220 + 175 + 500)/3 = 298.33 ohm-meter

By inspection, for approximation, method I will give me more conservative result than method II.

My question to experienced folks, is method I reasonable enough to approximate conversion of all three layers (a-c) to one top soil layer? Any alternatives?

Regards,




RE: Converting to Two Layer Soil Resistivity Model

The best alternative is to get the Wenner test measurements and probe spacings and calculate the best fit 2-layer soil model. Does ETAP have a module for calculating soil layer models from test results?

The best fit 2-layer soil model lower layer will not be the same as the bottom layer of the 4-layer soil model. It will have a different depth and resistivity.

Another option, probably not feasible in your situation, is to use a grounding analysis program that can use a 4-layer soil model (like CDEGS from SES).

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources