Vertical Electrical Sounding (VES)

Vertical Electrical Sounding (VES) is an electrical resistivity method which involves the rapid measurement of variations of the ground resistance with unit depth.

VES measurements are typically made by injecting an array of current electrodes or potential electrodes into the ground, at a set probe spacing. This creates an electric field allowing for the measurement of the potential and hence the calculation of the electrical resistance.

This can then be used to calculate the electrical resistivity at the centre of the deployed array, whereby varying the electrode spacings, builds up results to produce a 1D resistivity with depth sounding.

Applications of Vertical Electrical Sounding (VES)

VES surveys are widely used within geotechnical investigations and have many applications across the construction industry.

Due to its rapid acquisition, VES data is viewed as an excellent reconnaissance technique for clients to gain a quick and accurate picture of the soil's electrical properties to indicate different geological formations. This information on the different geological structures can then feed into their site designs.

Examples include:

Earthing Matt Systems

VES surveys are often undertaken to aid the design of Earthing Matt Systems by providing an estimate of the volume resistivity of the soils through which the current will flow.

This is achieved by deploying an array of electrodes over the proposed earthing system and measuring the resulting resistivity distribution profile.

Pipeline Routes

VES is used in the planning stages of pipeline routes to aid the design and installation of buried pipelines.

The results can be extremely important for the design of pipelines as the depth of burial will have a direct impact on the external corrosion protection requirements.

Landfill Mapping

The electrical conductivity of soils can be used as an indication of their waste content and VES data are therefore often used in the mapping of landfill sites.

This is achieved by deploying electrodes at fixed probe spacings and measuring the apparent resistivity values down through the waste horizons.

Groundwater Exploration

The measurement of the electrical resistivity of soils can be used as an indication of the presence of groundwater and VES measurements are often used to aid groundwater investigation.

Soil lithology

VES is a geophysical method that can also be used to aid the identification of soil lithology as changes in the electrical properties (resistivity contrast) of the geological medium often relate to changes in their physical properties.

Vertical Electrical Sounding (VES) FAQs

How does vertical electrical sounding work?

Vertical electrical sounding works by injecting current electrodes into the ground, at a set probe spacing, and measuring the potential to calculate the resistance.

This can then be used to calculate the resistivity at the centre of the deployed array, whereby varying the electrode spacings, builds up measurements to produce a 1D resistivity with depth sounding.

What is the Schlumberger method?

The Schlumberger method is the most common type of VES array used to map the subsurface lithology. Arrays of typically four electrodes (either potential or current electrodes) are set out with progressively increasing spacings between, with the depth of each measured point being a function of electrode spacing.

What is the Wenner method?

The Wenner method uses four electrodes arranged in a line. Two current electrodes are placed at a set spacing, with a potential electrode located midway between them. The Wenner method is commonly used to determine the resistivity of shallow, near-surface soils.

What are the benefits of Vertical Electrical Sounding (VES)?

Some of the benefits of VES include its versatility, speed and accuracy. VES can be used in a wide range of geologic settings and can be applied to both unconsolidated and bedrock aquifers. VES measurements are typically made quickly, allowing for rapid geophysical data acquisition.