4-Pin Wenner Array and Resistivity Imaging

Purpose: The 4-Pin Wenner Array and resistivity imaging methods are essential for assessing subsurface resistivity, often used in electrical grounding design, soil characterization, and site planning in industrial and geotechnical projects. These methods help define subsurface conductivity variations that inform construction, grounding systems, and environmental assessments.

Applications:

Electrical Grounding Design: Wenner Array surveys, performed according to ANSI/IEEE standards, provide resistivity data critical for designing effective grounding systems, especially in industrial areas with complex subsurface features.

Geotechnical and Environmental Studies: Resistivity imaging with multi-electrode setups maps subsurface layers, helping to detect geological changes, groundwater levels, and potential contamination zones.

Technical Process: The 4-Pin Wenner Array uses a Phoenix 3 kW transmitter and Scintrex IPR12 receiver to generate high-quality voltage readings over varied electrode spacings. This setup, powered by a Honda generator, enables clearer results in conductive environments. Additional surveys like GPR, EM31, and metal detection provide complementary data to ensure accuracy where buried utilities might interfere. For larger surveys, Iris Syscal equipment with up to 96 electrodes is used, with results processed in Loke and UBC 2D modeling software.

Key Uses: These methods provide accurate, high-resolution subsurface resistivity data essential for safe grounding designs and environmental assessments, with applications spanning industrial, environmental, and construction sectors.

4-Pin Wenner Array surveys are carried out as per ANSI/IEEE Std. 81-1983 and others as a guide (i.e., IEEE 80-2000 and ASTM G57 for soil resistivity test).  The work can be carried out for many applications such as to aid with appropriate electrical grounding design for planned facilities within highly congested industrial areas.

A Phoenix 3 kW transmitter with Scintrex IPR12 is used as the transmitter and receiver respectively.  The transmitter, which is powered by a Honda motor-generator, provides switch-selectable transmitter voltages that provide sufficiently high Vp’s at the receiver where required (e.g., for the larger “a”-spacings and more conductive settings).  New custom designed and manufactured stainless steel grade 316 electrodes measuring 12 inches long are used to keep burial depths consistent at all accurately measured and positioned injection and receiver points.

Typical instruments used for 4-Pin Wenner Array surveys for grounding design are battery operated.  The 3 kW MG operated transmitter used by ClearView is able to produce higher sustainable transmitter currents and higher Vp’s where required for the larger “a”-spacings and in more conductive areas.  Therefore, results are ‘cleaner’ compared to battery-operated systems because the measured amplitudes are larger for the MG operated Tx.  That is, minor fluctuations in measured transmitter currents and receiver voltages caused by factors such as electrode contact, near surface moisture, etc. are less significant for large values possible with the MG powered transmitter compared to smaller amplitude measurements that would be expected from a battery operated system.

Several additional geophysical survey methods can be carried out to characterize the sub-surface in the area: GPR at 250MHz and 100MHz, Geonics EM31 Ground Conductivity (vertical dipoles mode), and Geonics EM61 metal detection (standard coils).  Private locates with the Radiodetection gear is also completed.  The results from these additional surveys are important because buried facilities could interfere with and skew the 4-Pin Wenner Array results if located along or relatively near the spread.

Iris Syscal equipment acquires resistivity imaging data. This battery operated combined transmitter/receiver device can collect data for 96 electrodes spaced up to 10 metres apart. Pre-set Schlumberger and Wenner arrays cycle through for the desired exploration depth. The results model and present with both Loke and UBC 2D inversion modeling software.