BGS Resistivity

This theme provides information on the electrical resistivity of a geological material, to be used where the earthing characteristics of the ground are required.

The spatial model covers England, Scotland and Wales at 1:50 000-scale using data from these BGS datasets:

• Soil Parent Material Model
• National Geotechnical Property Database
• Geophysical Laboratories Database

The resistivity of geological units is an important factor in engineering activities where the electrical characteristics of the ground are required, e.g. in earthing of electrical systems. The resistivity of the ground is dependent on a number of factors, including pore water resistivity, saturation and the clay content of the underlying geology.

What is resistivity?

Electrical resistivity is an intrinsic property of a material and is measured as its resistance to current per unit length for a uniform cross-section. The national attribution of resistivity is based on the calculation of resistivity using the methodology published in An effective medium algorithm for calculating water saturations at any salinity or frequency (Berg (2007).

We hold several thousand field resistivity soundings but they cover a limited number of geological units and are unlikely to cover the lithological variation and saturation conditions that may be encountered. The Berg method uses a number of parameters that are known for the lithologies of many geological units (or can be reasonably estimated using knowledge of similar materials (from the datasets listed) and the field soundings results as a guide.

Who uses resistivity data?

Resistivity is of interest to a wide range of organisations concerned with development including:

• infrastructure
• utility companies
• local authorities
• green energy companies
• developers
• engineering consultants and contractors

Resistivity is particularly relevant to the major power distribution networks.

Classification

The Soil Parent Material Model of Great Britain, which describes the geology of the near surface, has been classified with modelled values of electrical resistivity. The description of the classification can be found in the free downloadable user guide.