Soil resistivity testing for earthing design

The performance of an earthing system depends directly on soil resistivity. For substations, solar and wind farms, telecom towers, industrial plants and residential buildings, the size of the earthing grid and the number and depth of electrodes are all calculated from this parameter.

We measure using the four-electrode Wenner method: electrodes are driven into the ground in a straight line at equal spacing, current is passed through the outer pair and voltage is measured across the inner pair. Changing the spacing gives resistivity at different depths, from which a two-layer or multi-layer soil model is built. Measuring along several directions across the site accounts for ground heterogeneity.

Soil resistivity is strongly affected by moisture, temperature, salinity and soil type, so the report records measurement conditions and seasonal factors. Where needed, deeper layers are investigated on the same site with vertical electrical sounding (VES).

Test points are positioned with GNSS RTK, and results are presented in tables and charts that electrical designers can use directly in their earthing calculation software.

When you need it

• Earthing design for electrical substations
• Solar and wind farm design
• Telecom towers and antenna masts
• Lightning protection for buildings and industrial sites
• Input data for cathodic protection of pipelines

What's included

• Planning test lines and points
• Wenner measurements at multiple spacings
• Repeat traverses in several directions
• Recording conditions (moisture, soil type)
• Building a layered soil model
• GNSS RTK positioning of test points

How we work

1. Obtaining design requirements and the site plan
2. Selecting test lines on site
3. Resistivity measurements
4. Data processing and soil modelling
5. Report handover

Deliverables

• Table of resistivity measurements
• Resistivity versus depth charts
• Layered soil model conclusion
• Test point layout and technical report