earth resistivity test report · pdf fileearth resistivity test report ... 3043-1987 on the...

2017

EARTH RESISTIVITY TEST REPORT

NAME OF THE PROJECT: STUDIES WORK FOR ANDHAPRADESH MEDTECH ZONE

(AMTZ), VISHAKHAPATNAM, ANDHAPRADESH

LOCATION: SUB‐STATION, ANDHAPRADESH

Report Ref. No: IDAX/REP/2017060007/FD‐ERT/2017‐18/424

TESTING AGENCY: IDAX CONSULTING & RESEARCH PVT.LTD. Plot No. - 5016, Duplex-E, Brundaban Enclave, VSS Nagar,

Bhubaneswar-751007, Odisha (INDIA).

Tel: +91-674-3199991, 2360019, Fax: +91-674-2360019

E-mail: [email protected]

Web: www.idaxconsulting.com

Date of Test: 06.07.2017

Date of Submission of Report: 08.07.2017

mailto:[email protected]

http://www.idaxconsulting.com/

IDAX CONSULTING & RESEARCH PVT.LTD.

Project Code‐ 2017060007_ERT Page 1 of 8

1. INTRODUCTION:

The Earth Resistivity Test (ERT) of soil was carried out at site for STUDIES WORK FOR

ANDHRAPRADESH MEDTECH ZONE (AMTZ), VISHAKHAPATNAM, ANDHRAPRADESH. with

the aim to determine an average value of electrical resistivity of soil for design of safe

earthing system. The Earth resistivity field test was done in 06/07/2017 at one location

given as directed by the client.

2. PURPOSE OF INVESTIGATION:

The purpose of this investigation is to determine an average value of electrical

resistivity of subsurface for design of safe earthing system with the help of

Microprocessor based electrical resistivity meter model DET-Auto.

3. GEOPHYSICAL INVESTIGATION:

Geophysical investigation was carried out as per IS: 3043-1987 on the basis of Earth

Resistivity meter model no. DET-Auto. Wenner’s four-electrode method is used to

determine the earth resistivity.

4. WENNER’S CONFIGURATION:

This is one of the most commonly used arrays proposed by Wenner in 1916. Four

electrodes A, B, M, and N are placed at the surface of the ground along a straight

symmetrically about a point O. The observation point in such a way that the distance

between AM = MN =NB = a., Where ‘a’ is called electrode separation see fig. 1.

Current ‘I’ is sent generally through outer electrodes A and B and the potential

difference (V) is measured between M and N. The instrument multification factor is f.

Apparent Resistivity, = 2aR (As per IS: 3043 – 1987, Clause No. : 36.3.1.2)

A a

M a

N a

B

I

V



5. Survey Procedure:

Resistivity sounding is used to make investigations along the depth. In this method

the center of configuration is kept fixed and measurements are made by successively

increasing electrode spacing. The apparent resistivity values obtained with increasing

values of electrode separations are used to estimate the thickness and resistivity of

the subsurface formations. In Wenner’s configuration all the four electrodes are

arranged in a line at a equal distance ‘a’ between the consecutive electrodes.

Measurements were taken at 1m,2m,3m & 5.0m. Current is sent through the outer

electrodes and the potential difference is measured between the inner electrodes.

The Resistance (R = V/I) is measured for each electrode separation and apparent

resistivity is calculated by multiplying value of ‘R’ with Wenner configuration factor

(2a), where ‘a’ is the uniform distance between the elctrodes. The computation of

the sounding data is discussed in the subsequent section.

6. Computation of Earth Resistivity:

When the earth resistivity readings for different electrode spacing in a direction are

within 20 to 30%, the soil is considered to be uniform. When the spacing is increased

gradually from low values, at a stage, it may be found that the resistivity readings are

more or less constant irrespective of the increase in the electrode spacing. The

resistivity for this spacing is noted and taken as the resistivity for that direction. In a

similar manner, resistivity for at least one equally spaced direction from the center of

the site are measured. These resistivity are plotted in a graph sheet in the appropriate

directions choosing a scale. A closed curve is plotted on the graph sheets jointing all

the resistivity points plotted to get the polar resistivity curve. The area inside the polar

resistivity curve is measured and equivalent circle of the same area is found out. The

radius of this equivalent circle is the average resistivity of the site under consideration.

The average resistivity thus obtained may be used for the design of the earthing grid

at that particular depth.



7. Results:

I. The electric resistivity test of the site were performed in 06/07/2017 at one location as

suggested by client.

II. Measured surface resistivity data is attached separately.

III. Average Resistivity / Equivalent Radius from polar curve is 14.927 ohm-m.

8. LIMITATION

The Electrical resistivity testing has been carried out at the location chosen by the

client. In general resistivity values are influenced by water, presence of dissolved ions

in soil media and nature of strata. Recommendations made in the report are hence

valid only for tested locations only. However if there is any change in subsoil

conditions and properties at places beyond chosen test locations, the soil consultants

to be contacted for further guidance.

For IDAX CONSULTING & RESEARCH PVT.LTD.

Engineer – Civil (Soil) Er. Pratiksha Ray B. Tech- Civil

(Head - Civil)

Er. Deepak Kumar Mallick

B. Tech (Hons.) – Civil (IIT Kharagpur)



DETERMINATION OF EARTH RESISTIVITY

CLIENT:

PROJECT :

ANDHRA PRADESH MEDTECH ZONE LIMITED

STUDIES WORK FOR ANDHAPRADESH MEDTECH ZONE (AMTZ), VISHAKHAPATNAM,

ANDHAPRADESH

LOCATION: SUB- STATION

CO-ORDINATES: N- 1950579.220 E- 79279.919

TEMPERATURE: 36.4°C HUMIDITY: 47%

PROJECT NO.: 2017060007

METHOD OF RESISTIVITY SURVEY : Wenner's Method as per IS:3043-1987

Direction: North

Test Electrodes

AB / 2

Test Electrodes

MN / 2

Distance

'a'

Resistance, Ohm

Current Factor Apparent

Resistivity

in m in m in m R = V / I f '' = 2aRf

1.50 0.50 1.00 2.460 1 15.457

3.00 1.00 2.00 1.000 1 12.566

4.50 1.50 3.00 1.000 1 18.850

7.50 2.50 5.00 0.360 1 11.310

Direction: North-East

Test Electrodes

AB / 2

Test Electrodes

MN / 2

Distance

'a'

Resistance, Ohm


Resistivity


1.50 0.50 1.00 2.000 1 12.566

3.00 1.00 2.00 0.860 1 10.807

4.50 1.50 3.00 0.590 1 11.121

7.50 2.50 5.00 0.300 1 9.425

Direction: East

Test Electrodes

AB / 2

Test Electrodes

MN / 2

Distance

'a'

Resistance, Ohm


Resistivity


1.50 0.50 1.00 1.120 1 7.037

3.00 1.00 2.00 0.770 1 9.676

4.50 1.50 3.00 0.490 1 9.236

7.50 2.50 5.00 0.390 1 12.252

Direction: South-East

Test Electrodes

AB / 2

Test Electrodes

MN / 2

Distance

'a'

Resistance, Ohm


Resistivity


1.50 0.50 1.00 0.990 1 6.220

3.00 1.00 2.00 0.910 1 11.435

4.50 1.50 3.00 0.750 1 14.137

7.50 2.50 5.00 0.470 1 14.765



Direction: South

Test Electrodes

AB / 2

Test Electrodes

MN / 2

Distance

'a' Resistance, Ohm Current Factor

Apparent

Resistivity


1.50 0.50 1.00 0.930 1 5.843

3.00 1.00 2.00 1.270 1 15.959

4.50 1.50 3.00 0.860 1 16.211

7.50 2.50 5.00 0.830 1 26.075

Direction: South-West

Test Electrodes

AB / 2

Test Electrodes

MN / 2

Distance

'a'

Resistance, Ohm


Resistivity


1.50 0.50 1.00 1.410 1 8.859

3.00 1.00 2.00 1.400 1 17.593

4.50 1.50 3.00 0.680 1 12.818

7.50 2.50 5.00 0.540 1 16.965

Direction: West

Test Electrodes

AB / 2

Test Electrodes

MN / 2

Distance

'a'

Resistance, Ohm


Resistivity


1.50 0.50 1.00 2.110 1 13.258

3.00 1.00 2.00 1.170 1 14.703

4.50 1.50 3.00 0.600 1 11.310

7.50 2.50 5.00 0.390 1 12.252

Direction: North-West

Test Electrodes

AB / 2

Test Electrodes

MN / 2

Distance

'a' Resistance, Ohm Current Factor

Apparent

Resistivity


1.50 0.50 1.00 2.520 1 15.834

3.00 1.00 2.00 1.690 1 21.237

4.50 1.50 3.00 0.770 1 14.514

7.50 2.50 5.00 0.550 1 17.279

Results of Electrical Resistivity

Wenner Method (IS-3043)

Project No: 2017060007

Client: ANDHRA PRADESH MEDTECH ZONE LIMITED

Project: STUDIES WORK FOR ANDHAPRADESH MEDTECH ZONE (AMTZ), VISHAKHAPATNAM, ANDHAPRADESH

Co-ordinates: N- 1950579.220 E- 79279.919

Temperature: 36.4°C Humidity: 47%

Location SUB- STATION

Method of Resistivity Survey: Wenner's Method

Electric Resistivity: r in ohm-meter = 2aR (Ω.m)

where a = Distance between two successive electrodes in meter (m)

R = V/I = Resistance in ohm (Ω)

Sr. No.

Electrodes

AB / 2

Electrodes

MN / 2

Distancs

'a'

Direction of Test

Avg.

Resistivity

at Depth

Maximum

Resistivity

at Depth

Minimum

Resistivity

at Depth

North North-East East South-East South South-West West Nourth West

m m m R (Ω) f ρ(Ω.m) R (Ω) f ρ(Ω.m) R (Ω) f ρ(Ω.m) R (Ω) f ρ(Ω.m) R (Ω) f ρ(Ω.m) R (Ω) f ρ(Ω.m) R (Ω) f ρ(Ω.m) R (Ω) f ρ(Ω.m) ρavg(Ω.m) ρmax(Ω.m) ρmin(Ω.m)

1 1.50 0.50 1.00 2.460 1 15.457 2.000 1 12.566 1.120 1 7.037 0.990 1 6.220 0.930 1 5.843 1.410 1 8.859 2.110 1 13.258 2.520 1 15.834 10.634 15.834 5.843

2 3.00 1.00 2.00 1.000 1 12.566 0.860 1 10.807 0.770 1 9.676 0.910 1 11.435 1.270 1 15.959 1.400 1 17.593 1.170 1 14.703 1.690 1 21.237 14.247 21.237 9.676

3 4.50 1.50 3.00 1.000 1 18.850 0.590 1 11.121 0.490 1 9.236 0.750 1 14.137 0.860 1 16.211 0.680 1 12.818 0.600 1 11.310 0.770 1 14.514 13.525 18.850 9.236

4 7.50 2.50 5.00 0.360 1 11.310 0.300 1 9.425 0.390 1 12.252 0.470 1 14.765 0.830 1 26.075 0.540 1 16.965 0.390 1 12.252 0.550 1 17.279 15.040 26.075 9.425

Average Resistivity in Direction

14.546

10.980

9.550

11.640

16.022

14.059

12.881

17.216 13.362

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